Challenges in Composites Testing Masterclass

On 2nd December, Instron had the great pleasure of hosting a composites-focused masterclass for customers, based at our European Headquarters in High Wycombe, England.

Focused around a combination of seminars and active workshops, our customers were involved in discussions surrounding a wide variety of composites-based testing challenges, from the importance of specimen alignment, to dynamic testing and advanced measurements, as well as productivity of testing and strain measurement.

We were also pleased to host Nigel O’Dea (Founder and Director of OB2B Industrial Marketing & PR) who brought with him 25 years of industry experience. His involvement and presentation reinforced the importance of the global strategic growth and challenges faced within the composites industry.

At the end of the masterclass, all customers were invited to stay on for a sneak peek around the newly vamped factory floor and had the opportunity to get hands on with a variety of demonstration machines hosted in our Applications Lab.

Overall, the masterclass proved to be an insightful look into the challenges of composites testing, and also an opportunity for great discussion between customers and our dedicated applications specialists. Here’s what one of our customers had to say about the day:

“Very well run event, all the speakers were very approachable. It totally reinforced the message that Instron is a key partner for materials testing and able to share helpful, up-to-date knowledge and insight, not just a test machine supplier.”

We will be running similar events throughout 2015; so, look out for new dates being confirmed on our website.


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Developing Standards for Non-Standard Biotechnology

The medical device industry is consistently challenged to supply safe and effective solutions for the end user, considering unique patient needs and conditions.

With the development of new technologies, including biodegradable materials, cell therapy, or combination devices, the inherent variability and difficulty of standardizing testing methods exponentially increases. To address these emerging challenges, the standards community has been developing working groups comprised of industry, research, clinic, and patients to holistically evaluate how these advances affect and will affect standards.

Read the Quality Magazine article for the full story.
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Tips & Tricks for Packaging Testing

Explore best practices to better provide quantitative information about tear resistance, puncture resistance, peel strength, heat seal strength, and durability of materials used in flexible and rigid packaging, and finished packaging products.

Tips & Tricks for Packaging Testing from Instron

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Helping to Standardize High-Rate Testing of Composites

Instron has joined a new international group that is seeking to develop a best practice guide and test standards specifically for testing composites at high-strain rates.

As the automotive industry seeks ever-more-urgently to embrace composites, there is an increasing demand for testing composite material behavior at high-strain rates. The need for detailed data to inform crash simulation models first drove a renewed demand for equipment over the last 3 years, and now there is a need for international standardization in methodologies and data handling. The group’s aim is to facilitate generation and exchange of reliable and comparable test data in this highly challenging area.

The working group has been coordinated by the University of Dayton Research Institute, and currently composes about 20 organizations including major automotive manufacturers, composite materials producers, test houses, and research institutes. As a world leader in high-rate servohydraulic testing systems, the dynamic systems team at Instron are very pleased to share their expertise with this initiative that will make a tangible difference to the industry. Similarly, Instron CEAST will be contributing to work on drop-weight based techniques for high rate testing.

The working group is looking for more European contributors especially, but we would strongly encourage all our customers with expertise in this area to join us in supporting the project. Please feel free to contact Instron applications specialist, Dr. Peter Bailey, if you would like to know more.

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A Case for Extensometry

A universal testing system very simply measures 2 things during a basic mechanical test: force (via the load cell) and displacement (via the crosshead encoder). To obtain a basic stress-strain curve, you might think that’s all you need. With the force measurement from the load cell, the cross-sectional area of the material can be used to calculate stress; and with the crosshead extension, the original distance between the grips or fixtures can be used to calculate strain throughout the test. How simple!

It may be simple, but it’s not the best option for all material tests. Even when using the proper equipment for your test – machine, load cell, grips, fixtures, etc. – the system is compliant, i.e., it bends and stretches a little bit when you’re running a test! This means that what the crosshead encoder is reading and sending to the software may not truly represent the distance your specimen has travelled. But don’t panic just yet! This is the fundamental reason why we use extensometry in materials tests. An extensometer measures strain directly at the specimen – only taking into account the strain directly at the material, and not anywhere else in the system (the crosshead, the grips, the load cell, the couplings, etc.).

International testing standards will specify if extensometery is required for your testing – so have a look through the standards you follow and make sure you’re using the proper device for your tests. Aren't following a standard? Here are some recommended cases where you should use extensometry:

• Stiff materials (composites, metals, plastics)
• Quality control environments 
• Comparing different materials
• Comparing the same material on different machines
• When you want truly accurate strain data!

Note that some extensometers work best for certain materials and situations. If you’re not sure which you should use for your test, we’ll be happy to help you figure it out.

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Challenges of Rigorous Demands

The world of materials testing is changing …

• materials are getting stronger, stiffer, and lighter 
• test standards are becoming stricter 
• testing labs are asked to perform more complex analytical tests

With all of these changes affecting the way labs test, it’s important to think about the following questions: How does your lab environment challenge test results? Is your lab equipped to handle the new strength of specimens? Are you testing under load or position control parameters, or do you require the use of strain control?

These questions, when coupled with the changes above, are all factors we have discussed with our customers and are sharing with you.

Challenge #1

The automotive and aerospace industries are growing and demanding that materials become stiffer, stronger, and lighter. This new breed of materials is helping the industry produce lighter and stronger products, but lab operators are finding that the large energy release may damage contacting extensometers. To reduce the cost of maintenance for labs testing these challenging materials, video extensometers are an ideal  solution – they don’t contact the material, and therefore, they are unaffected by the high-energy breaks of materials, such as carbon fiber composites or rebar.

Challenge #2

With the growing demands come newer standards that place stricter requirements on the type of extensometer you are allowed to use. For example, ISO 527-2012 now requires that devices have an accuracy of just 1 micron in order to measure the modulus of the material. 1 micron is exceptionally small (about 100 times smaller than the width of the average human hair) and is exceedingly difficult to measure. Although this accuracy can be attained with some traditional clip-on extensometers, clip-ons have limited travel and typically can’t measure strain through failure for ductile specimens. In addition, they may cause premature failure due to stress risers from knife edge contact.

Until recently, there hasn't been a video device that could meet the new standard requirement due to problems with lighting and air flow that naturally occurs within a lab, which ultimately affects the device’s ability to provide accurate results.

To prevent the lab lighting from making a difference, we have incorporated a patented lighting system into our new video extensometer that floods the specimen with polarized light and use a polarized filter on the lens. This enables the video extensometer to produce consistent results no matter the lighting conditions, including flicker from fluorescent lights or the difference in lighting from a lab window.

Secondly, all video systems are affected by air flows in the room from sources like air ducts and heat sources. These air flows are similar to what you may see on asphalt on a hot day. The air currents and heat sources in your lab are probably much smaller, but since 1 micron is so small even minor perturbations make the measurement impossible. Our engineers incorporated a patented system of fans into the video extensometer to prevent these air flows between the specimen and the camera, enabling the test to yield accurate results whether your air system is off or running at full speed.

Challenge #3

New standards are also placing requirements on the way that tests are being controlled. In the past, most – if not all – tests were run under load or position control parameters, but newer standards may prefer or require the use of strain control. This can be done with contacting extensometers, while pre-existing video extensometers struggle to run strain control tests because the images taken have to be processed by the computer and then sent to the software to adjust the frame movement accordingly. There is a large delay between the images being taken and the processing by the computer, which means that by the time the frame reacts to the strain measurement the value has changed.


To resolve this, the new video extensometer now measures strain at the camera in real time and then sends the data directly to your test frame. This drastically reduces the response time of the camera and allows for clean strain control.

Challenge #4

Extensometers are excellent for materials testing, but only give you a point-to-point measurement. Other measurement techniques, such as digital image correlation, can give you more information about material behavior during a mechanical test, but they typically require expensive and complicated equipment and software. Because of the high barrier to entry, only a few labs take advantage of this technology and are able to make key insights about their material behavior that other labs can’t.

Instron has lowered the barrier to entry for digital image correlation by offering our video extensometers along with dedicated digital image correlation software. The extensometer images are automatically synchronized in time to the data from the load frame, which means that you can now run a test and begin producing full field strain maps in less than one minute. Read more

Question From A Customer: Air Bubbles In Extrudate

Q: We have an MF30 Melt Flow Indexer and started running tests on various polymers in our lab. Some of the samples have a lot of air bubbles in them. I believe this is contributing to inconsistencies in melt flow values. How do we minimize this?

A: There are a lot of reasons you could be seeing air bubbles in the filament sample. Ultimately, it comes down to keeping the testing and cleaning processes as consistent as possible. To start, keep the following points in mind:

1. The form of test sample can affect how the material melts within the barrel. Pellets or granules are the most consistent. Flakes, bits of component, and powders are not as easily compounded and may leave small air pockets, resulting in air bubbles in the melted sample.


2. It is necessary that the sample be compacted with a suitable and repeatable pressure. For some materials. hand-pressure is fine, while a higher force may be necessary for others. Too little or too much pressure can allow the sample to swell or trap air bubbles. Keep in mind that some materials are more sensitive to operator-to-operator inconsistencies than others.


3. Preconditioning is an important part of preparing the sample for melt flow testing, especially for hygroscopic materials, such as PET or PA. Excess water gets trapped inside the material and generates gases when heated, which often triggers degradation processes within the sample. Degradation can also be promoted by residuals of sample from previous tests, when the barrel is not cleaned properly.

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The World of Automation for Materials Testing

Imagine your ideal day in the lab … Time on your hands to get work done, a safe environment for testing, and consistent test results that ultimately increase throughput. We hear from a lot of our customers – regardless of their application – that they are always looking for ways to improve their testing productivity and operator safety.

Using an automated testing system in your lab brings this new dimension of testing productivity directly to you: maximize efficiency by testing hundreds of specimens all the while the next specimen is being prepared; enable precise and consistent placement of specimens to eliminate errors; and ensure operator safety by alleviating safety gripping hazards.  This assisted process promotes maximum efficiency as skilled operators can focus on other priorities and testing can occur at a continuous and consistent pace.

Watch as the system runs with no operator intervention.

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Evaluating the Quality of High-Performance Plastics Molding

When chemical companies invest in developing high-performance polymers—such as filled polyesters, PA, PC, LCP, and PEEK—to engineer automotive and electronic components, they could potentially experience issues with a high melting temperature during the injection molding phase. It’s crucial to understand that even if the mold filling has been successfully executed, the molded parts can still show significant failures, such as cracks or warps and aesthetic defects. Therefore, those parts need to be discarded as the products’ quality has been affected. These production complications create material waste, inefficient machine time, increased operator labor, and decreased profitability.

Different techniques, carried out with dedicated equipment and experienced personnel, can be used for high-performance polymers analysis. However, this requires a lot of effort and delivers results from various sources, which often can’t be combined. This complex scenario can be simplified by using a capillary rheometer. 

R&D managers can test the materials before production with a capillary rheometer and simulate the material behavior under processing conditions. With the pvT accessory device, it is possible to estimate how the pressure and temperature affect the change in volume of polymers during the injection molding process.

The capillary rheometer equipped with the pvT device removes the production pains, making it possible for R&D to keep up with technological trends and the emerging high-performance polymer applications. Read more

How to Address Challenges in QC Medical Device Testing

We are proud to share that Meredith Platt, Director of Marketing & Emerging Markets for the Electromechanical Business, presented at the recent MEDTEC China event in September.

As Instron has developed many insights working with our customers in the biomedical industry, Meredith discussed challenges that QC laboratories encounter when testing a variety of medical devices, ranging from stents to catheters to spinal implants. Supporting the full product life cycle, she shared engineering solutions to assist product development, prototype evaluation, manufacturing, and delivery.

Here's a peek at her presentation:

ChallengesQCMedicalDeviceTesting_Sept2014 from Instron

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Is Design Validation Slowing Down Your Time To Market?

Instron interacts with many new product development labs that have a need to validate their new product or component design. Often part of this design validation requires mechanical testing. We have noticed a common need in these research and development labs to perform rapid "what if" analysis during design validation. That is, a test engineer often does not know the test speed, end of test value, etc. before pressing the start button on their Instron frame. Often the mechanical test is iterative and takes a trial-and-error approach. This type of "what if" analysis can be accelerated by using Expression Builder-driven parameters in Instron's Bluehill^® 3 Software.

Example:

You do not know the test speed or what maximum load you will need to apply to your product. So, you want to try several speeds and loads until the results look correct.

Add these variables as number inputs:

Using Expression Builder, select the number inputs appropriately for your test:

Now, in the workspace, you can simply type in different test speeds or maximum load criteria to validate your product taking a trial-and-error approach.

Using Expression Builder within Bluehill 3 should expedite your design validation process.

To learn more about the benefits of Expression Builder, this video may be helpful.

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Stress Control and Yielding Material

Since the first materials testing machines were used for tensile testing of metals, one option of performing the test has been to control the rate at which you apply load to the specimen, or apply stress. This technique has been successfully used on manual hydraulic machines from the beginning of the 20th century, if not before. Manual valves are opened to adjust the flow rate of oil into the actuator; the loading rate is then checked against a large force dial. Once the desired stressing rate has been achieved, the values are left at the same setting so the flow of oil remains constant. This enables the testing machine to run at the same crosshead separation rate for the remainder of the test, or until the test is expedited.

The same test method is still used in major metals tensile testing standards today, e.g. ISO 6892-1 & ASTM E8. When using a modern test system with electronic controllers, the test setup needs to be slightly different. If the control mode for calculating proof stress is set as "tensile stress" (or similar), the machine will try to continually increase the stress at the rate you requested. During yielding, this can result in the crosshead speed increasing exponentially, resulting in far higher strain rates. When testing strain rate sensitive materials, this can lead to large proof stress discrepancies.

To overcome this, testing systems are set up so that the first stage of a test is in stress control. Once the correct rate is achieved, the crosshead speed is then calculated and locked in. This enables the machine to operate in an equivalent manner as their older hydraulic counterparts.

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How to Test Lap-Shear Specimens

Manufacturing processes are moving away from using traditional bolts and rivets to using new, stronger adhesives to hold together materials such as composites and aluminum. With this increase in bonded manufacturing, it is more important than ever to accurately test the adhesive strength of bonds to prevent catastrophic failures.   

There are several tests which are important for adhesives, but the most difficult to perform well is the lap-shear test. In this test, two pieces of material are bonded together and then pulled apart to generate a shear force on the adhesive with no peeling force.

This test can be performed in various ways, but it’s important to understand each one because some may produce results which are drastically lower than expected due to peeling forces.

Adhesively Bonded Rigid Plastic Lap-Shear Joints

The Wrong Way

1.)  No tabs in grips without offsets

a.)  This method is not preferred because the bond line is not in the center of the test axis. It will produce lower max loads than other methods and may result in more rejected materials. Some people may use this method because it requires simple equipment and minimal specimen prep time.

The Right Ways

2.)  Tabs on specimens in grips without offsets

a.)  To perform this test, a user will bond the two pieces together, and then on each end, bond a small additional piece as a tab. With this method, the center of the test axis is aligned with the center of the adhesive, but it requires expertise and extra specimen prep.

b.)  If the tabs are not the right thickness or if the adhesive bonds are too thick or thin, the values produced may still be lower than expected.

3.)  Placing spacers in grips without offsets

a.)  This method requires the user to place pieces of material in the grips with the specimen to keep the bond line in the center of the grip. This can be difficult because the spacer must be identical to the thickness of the specimen and the bond line. If the thickness is not right, then the results produced will be lower than expected.

4.)  Double lap-shear in grips without offsets

a.)  The typical lap-shear specimen is bonded with two additional pieces of material to produce accurate results. This requires extra time, material, and expertise to prepare the specimens properly.

The Best Way

5.)  Untabbed specimens in grips with offsets

a.)  To perform this test, the jaws of the grip are offset to hold the specimen while keeping the adhesive bond line in the test axis. There is no extra specimen prep required for this type of test allowing it to be performed quickly and produce accurate results. Instron offers several grips that can perform this test including the precision mechanical wedge grips.

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Understanding Melt Flow Testing and Its Importance

Melt flow testing is simply a measure of the flow of a polymer when melted. The result of a melt flow test, called the melt mass-flow rate (MFR) or melt volume-flow rate (MVR), is defined as the amount of mass or volume of a polymer that flows through a small die at a specified temperature and pressure.

The melt flow test itself is simple and straightforward. A small amount of a thermoplastic sample (usually in granule or flake form) is heated in a barrel at a specified temperature, melted to a viscous fluid, and is forced out of a capillary die by a piston loaded with dead weights. Once enough sample extrudate has exited the die, it is removed and weighed, or the volume of the sample is measured by the machine.

ASTM D1238 and ISO 1133 are the most common standards for melt flow tests and define the equipment specifications, as well as test methods. Because various temperatures and weights are allowed for melt flow tests (only suggestions for each material type), test parameters always need to be reported with MFR/MVR results.

Note: Imagery is a simple representation and not to scale.

Typically, the MFR/MVR of a polymer is inversely proportional to its molecular weight. Though not frequently used in R&D settings, melt flow testing is very common in quality control and process control laboratories. It is mostly seen in compounding or manufacturing/converting facilities.


What do you gain from melt flow testing?

• A typical index value for verifying in-house material
• Quality check of entrance materials
• Comparison of new materials in a product development setting
• Evaluation tool for new material suppliers
• Quick comparisons of batches of material 
• Estimation of flow properties for simple extrusion processes 
• Predictions of how a polymer will behave in a number of processing techniques

If you are not currently performing melt flow tests, but think you should be, contact us for guidance on selecting the proper equipment for your laboratory. Read more

Helping to Provide the Good Housekeeping Seal of Approval

Ever wonder how the beauty industry can make their claims? Research and testing is behind the development of beauty products to determine the best technologies, formulas, and products to meet goals. When consumers want to hear the validity of the claims, they look to outside sources for evidence.

Good Housekeeping tested a variety of hair products in their Beauty Lab to find the winners of the Anti-Aging Hair Awards. To test how those products impact the strength of hair, technicians used a comb fixture on an Instron system. The Good Housekeeping team measured "friction experienced when [the fixture] moved through a wet or dry hair swatch".  Simulating what happens in real life instilled confidence in consumers to purchase those winning products.

Instron comb fixture for testing hair products

Here is another example of an Instron system performing a tensile test on hair to determine strength before and after a product is used. Read more

Testing a Student-Made Off-Road Vehicle

When Northeastern University students visited our Norwood, MA headquarters, Instron employees had a chance to ride an off-road vehicle. As a platinum sponsor, Instron assisted the student engineers in their quest to finish first.

Instron employees taking a ride in the student-designed car

For the Baja SAE Collegiate Design Series, students from across the globe design, build, and race off-road vehicles in competitions around the United States. Young engineers are challenged to build an off-road vehicle with open wheels and one-passenger seating. For a year, they work together creating the cars and being tested in an industrial market, where they need to promote and finance their projects.

The Northeastern Baja team focuses on endurance and high-performance in the Baja SAE events. To get ahead the competition, this year's car featured handlebar steering and a six-speed manual transmission. Led by Dalton Colen and Matt Nussbaum, the group finished 8th in the Baja SAE competition in Illinois. In each of the past three years, Northeastern has finished in the top ten for the endurance test and overall race at an event.

We wish them luck next year and hope they come back to visit! Read more

Preloading, and How It Affects Your Mechanical Test

It is almost always recommended that the Bluehill^® Software preload feature be used when you’re performing a mechanical test. Preloading simply removes slack from the load string before a test begins. This is done by loading the specimen at a specified rate - called "preload speed" -  until a particular load limit is reached - called "preload". Note that this value should be high enough that it removes slack from your load string, but low enough that it doesn’t interfere with important early-test calculations like modulus or yield. Once the preload is reached, the software begins collecting data from the load cell, crosshead encoder, and any other measurement device you have in the system. That means your test begins collecting load data after it’s reached the preload value. It also means your first recorded load point will be the preload value and not zero—which is okay! There are also calculations, like slack correction, that allow you to remove what is called the “tow” section of the curve (Section B in the image below).

Once the preload is reached, Bluehill gives you the option to perform an auto-balance of your physical or virtual measurements. Any strain source, whether it is the crosshead extension or an extensometer, should be auto-balanced after the preload is reached. This ensures that all of the specimens in your sample start from the same load and strain point, making your data more accurate and much easier to process (especially if you are using extension and strain-based calculations).  If using extension as your strain source, keep in mind that your gauge length is now equal to the original gauge length plus the distance traveled to reach the preload. You should not auto-balance the load signal. We commonly see load being balanced incorrectly (see my post on balancing load cells). Once a specimen is gripped, it is common to see a bit of force on the load cell—either positive or negative. This is simply a function of how the grips hold the specimen, or it is due to the mass of the specimen. If the force recorded on the load cell is severe, it may be due to misaligned grips or a poorly-inserted specimen. If a specimen is brittle or fragile, a feature such as Specimen Protect can be used to ensure the load on the specimen does not exceed a specified amount (+/-) before beginning a test.

Effectively using the preloading and auto-balancing features of Bluehill can help keep your results much more consistent. If you have questions on how to incorporate these features into your tests, feel free to contact us.

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What Are Biodegradable Medical Devices?

What are biodegradable medical devices? They are the next hot medical device, one that only lasts a few months and then disappears without surgery or long-term side effects. Researchers around the globe are using new polymers and metals to design biodegradable medical devices. The devices do their jobs as long as needed and then dissolve, leaving the newly repaired tissue able to function normally.

Dr. Y. Yun at North Carolina Agriculture and Technical College (NACT) is using a combination LumeGen (flow/pressure) and CartiGen (compression) bioreactor system and an ElectroPuls™ E3000 to evaluate new biodegradable materials, design new components, and fatigue test new medical devices. He believes that biodegradable metal (magnesium) devices are greatly affected by their application in the human body; therefore, they should be tested in an environment that mimics this environment. Dr. Yun will be using Instron LumeGen system to evaluate biodegradable stents under physiologic pressure and flow conditions and the CartiGen to evaluate biodegradable screws under physiologic loading conditions. This in vitro test bed provides an alternative in vivo (animal testing) in which the experimental design is often limited due to high cost and results in inconclusive data. Dr. Yun hopes to reduce the gap between in vitro and in vivo testing with the Instron solutions. Read more

Automated XY Stage System Preventing Shattered Glass and Inaccurate Data

A pharmaceutical customer came to us with what they thought was a simple, low force, compression testing procedure that they wanted to automate to keep pace with increasing product testing demands.

What we found was an unreliable testing procedure that was time consuming, all manual, and completely operator dependent. The operator pulled a lever to set the applied force and manually record data. If the lever was pulled too quickly, the product would shatter and any obtained data was rendered useless (not to mention the safety hazard of cleaning up the broken pieces, including glass and potentially dangerous liquid).

We had a better solution that would not only be operator independent but also would allow more product testing in less time, leaving operators more time to perform other valuable tasks. The Automated XY Stage System provided the customer a reliable, repeatable, and safe way to test their product, complete with a product containment fixture that made the system easy to load. The solution resulted in increased efficiency and less wasted product. The customer was able to produce a better product due to a reliable testing procedure and more data in a shorter amount of time.

Now, an operator only needs to load a fixture, enter a few fields into the software, and press "run". While the system runs, the operator is free to walk away and address other needs. Read more

Oyster Glue Inspiring Stronger Adhesives

 
What adhesive is so strong that it sets wet? That's right: naturally produced oyster glue.

Chemist Jonathan Wilker from Purdue University focuses his research on this cement that allows oysters to attach to surfaces and each other, even throughout storms. Wilker's team also studies mussel glue, which is less strong compared to oyster glue, but has the same ability to set underwater. To evaluate the strength of these marine adhesives, Wilker and his team use an Instron electromechanical testing system.

Credit: Jonathan Wilker of Purdue University, NSF

Wilker is passionate about his findings because he knows how they may advance the biomedical world's development of surgical adhesives to seal body tissue and bone while a patient undergoes surgery.

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High-Frequency Testing of Nitinol Wire

Nitinol wire is a superelastic alloy with unique shape-memory properties that render it especially useful for a variety of different applications across industries. As nitinol requires a great deal of motion and flexibility in its applications, mechanical testing of nitinol must reach very high fatigue strains.

In an example of testing nitinol, the nitinol rod was clamped in place on the ElectroPuls™ E3000 using 3 kN pneumatic grips and flat serrated grip faces. Gripping pressure needed to be sufficient so the specimen did not slip during testing, but not so high that the grip faces created indentations in the nitinol. The test was run in load control between 10–700 N of tension with a triangular waveform. The frequency of the test was increased sequentially in blocks of 0.01Hz, 1Hz, 10Hz, 30Hz and 60 Hz, and the metal was expected to exert an elongation of approximately 7%.

High-frequency, high-capacity testing creates several challenges around specimen gripping, achieving load peaks, and quick increases in frequency. Slippage can become a problem if nitinol specimens are in the form of rounded rods or wire and relatively high loads are being applied. Instron has solved the issue of specimen slippage with wedge action pneumatic grips, which apply an increased gripping force as tensile load is increased. This ensures that the nitinol remains secure for the duration of the test.

E3000 with Pneumatic Grips and a Metal Rod

It is also essential to achieve the desired load peaks of 700 N for this test. Attaining load peaks can become more of a challenge as higher frequencies come into effect. The Amplitude Control feature of WaveMatrix™ Software ensures that the load peaks are met for each cycle and the desired 700 N of tension is achieved. Without this useful Amplitude Control feature, load peaks would likely drop below the desired 700 N of tension, especially as the frequency was increased. Read more

Consumer Reports Uses Instron for Bend Testing Smartphone

Consumer Reports sought to test LG's G Flex smartphone, which claims to bend to life's curves. The material properties of rigid plastic, aluminum, and glass typically are used in mobile devices, and one would assume they would be difficult to bend.

LG has claimed that the smartphone can withstand 88 pounds (about 40 kilograms), but the bendability is limited: "Do not bend inward or twist." Watch Consumer Reports prove that the G Flex phone can withstand more than LG indicated.

This video reveals the amount of load placed on the electronic device with an Instron system:

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Quick Tips for Balancing Load Cells

Whether you use bathroom scales, digital kitchen scales, spring scales – or any other measuring instrument, for that matter – you know the importance of zeroing it before it’s used. Failure to do so results in a shift in weight and thus, an incorrect reading on the scale. Now let’s think about the load cell in your testing system, which is just like a scale …

Prior to testing a batch of specimens, you should ensure that your load cell is properly calibrated and balanced – both actions are done right in the software. In Bluehill^® 3, this can be done from the console at the top of the screen. Simply click on the load cell icon, and then click "Calibrate". We refer to this as a software calibration (or “soft-cal”), which also balances the load cell.

Here are some soft-cal quick tips:

1. We recommend that the machine and load cell be switched on for about 15 minutes prior to performing a soft calibration. This allows the device to warm up, reducing the chances of drift.
2. Make sure you are not gripping a specimen when you perform a soft-calibration. It is okay to leave the upper grip or fixture attached to the load cell during the calibration – but it is also okay to leave it off. Just remember to perform an additional balance once the grip or fixture is added to the load cell.
3. Again, do not balance the load cell once the specimen is loaded into a grip or fixture. The force you see is real mass of the specimen, or force on the load cell. Balancing out this load would be like balancing a scale after you have put one foot on it (Note: this means the load cell should not be auto-balanced after preload). 
4. Though many systems will automatically recognize a load cell and restore its previous calibration every time it is plugged into the system, it is good practice to perform this soft-cal regularly, especially if swapping load cells. What does regularly mean for your system? Contact us, and we’ll help you figure it out.

Remember that a soft-calibration is not a replacement for on-site verifications by Instron Professional Services on a regular basis. For most laboratories, this means at least once a year, but your industry standards or internal protocols may differ.

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What is the Best Way to Grip Thin-walled Steel Tubes for Tension Testing?

Q. What is the Best Way to Grip Thin-walled Steel Tubes for Tension Testing?

A. For testing most tubular specimens, you should use vee-serrated grip jaws. They hold the specimen securely and the vee face ensures that the specimen is centered. However, the grip forces can deform thin-walled tubes. You should manufacture close-fitting mandrels with a tapered end to insert into the tube ends before gripping the tube. The mandrel will ensure the tube cross-section does not deform, and the tapered ends will accommodate any necking of the tube during testing. Read more

WPI Students Test ACL Graft Pretension Methods

At Worcester Polytechnic Institute's Biomedical Engineering Symposium, biomedical engineering students presented their research on anterior cruciate ligament (ACL) grafts. With an Instron electromechanical testing system, the students were able to analyze stress relaxation and creep techniques used for pretensioning before attaching ACL grafts in reconstructive surgery.

After ACL injuries, the wounded tend to undergo reconstructive surgery to insert grafts for knee rehabilitation. Over time, the ACL grafts lose tension strength. To prevent this, creep and stress relaxation methods are used on the grafts. Although relaxation techniques are common, universal standards are not used in evaluation of the best method.

Therefore, the students tested various protocols. Stress ratios between 15-minute pretensioning methods were significantly different: stress relaxation (0.47 ± 0.008) and creep (0.62 ± 0.005). This demonstrated that a creep protocol offers greater load retention after ACL reconstructive surgery. Interestingly, no significant difference was found when comparing 5-minute creep (0.63 ± 0.017) to 15-minute stress relaxation (0.47 ± 0.008). These results demonstrated the potential for physicians to save time in the operating room.

Instron was proud to attend symposium and watch WPI students Spencer Keilich, Allison Indyk, Jeremy Kibby, and Shreyas Renganathan present their fascinating research.

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Extensometer Slippage

Some of our customers are frustrated when they experience slippage of their strain gauge extensometers. Close examination of their extensometer knife-edges often reveals wear that has rounded the edge, increasing the likelihood of slippage. If you are experiencing extensometer slippage, take a close look at your knife-edges. For replacement parts, please contact your local Instron representative.

Note that the knife-edges are precision engineered to ensure an accurate gauge length, so we do not recommend that you attempt to sharpen the edges yourself. Read more

Efficiency of Continuously Increasing Load During Tests

This month, Instron hydraulic wedge grips had the privilege to be on the cover of Materials Testing, a German-English materials testing journal. The journal published an article by an Instron customer about testing the fatigue behavior of construction materials.

Microstructure-Oriented Fatigue Assessment of Construction Materials and Joints Using Short-Time Load Increase Procedure is written by Dr. Ing. Frank Walther, a professor of materials testing engineering (WPT) at TU Dortmund University in Germany. The article follows fatigue testing of construction materials with increasing load. Instron's WaveMatrix™ Software allows test runs with continuously increasing load using its "Calculations" and "Advanced Control" modules.

In Walther's experimental test, he used a servo-hydraulic testing system with Instron hydraulic wedge grips. During the test, various environments and manufacturing processes were used to determine how the conditions impacted the fatigue breakage. The fatigue load was increased frequently to determine the cyclic hardening and softening response as well as the cyclic characteristics impact on fatigue strength. Pleasantly, Walther found that this application of continuously adding load actually resulted in thorough data in a short amount of time.

Talk about efficiency!

Walther's experiment with Instron hydraulic wedge grips as seen in Materials Testing

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Additive Manufacturing Contest at the SAMPE Seattle Conference

A 57.15 mm tall and .0193 kg vertical support column withstood 4413.9 pound force at the SAMPE Seattle 2014 Conference, where Instron provided a 5969 Dual Column Testing System for the Student Additive Manufacturing Contest.

The winning column before and after bearing 4413.9 lbf with an Instron 5969 machine

The Society for the Advancement of Material and Process Engineering (SAMPE) is a professional engineering society providing a community to share information on materials and process technology. At the SAMPE Seattle 2014 Conference June 2-5, professionals met for an international exhibition and conference aimed at education and networking. Apart from the Additive Manufacturing Contest, the Student Bridge Contest was another opportunity which allowed students to created miniature bridge structures with composite materials and compete against one another.

The competing vertical support columns

Instron was at the conference to engage with society members and sponsor the Student Additive Manufacturing Contest. For the contest, high school and college students designed vertical support columns that were then printed with a Stratasys 3D printer in Seattle and tested between platens of an Instron load frame. Joe Vanherweg from California Polytechnic State University came in first place with a column that held 4413.9 lbf. For a prize, he won a Stratasys MakerBot 3D printer.

Congratulations, Joe!

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How Do You Prepare Your Specimens?

Depending on the materials you are testing and the size of your test lab, there are a multitude of ways to prepare materials testing specimens. 

For more rigid materials like metals, composites and hard plastics, there are specialized and dedicated machining or molding processes. For more flexible materials, such as plastic films, elastomers and soft plastics, there are many more options, since it is more feasible to cut these by hand.

If you are cutting specimens by hand, either with scissors, paper cutters, or other manual processes such as hollow dies and mallets, you should be aware that this can be detrimental to your subsequent tensile test results. Of course, for any specimen preparation procedure, there should be best practices set in place to ensure maximum consistency and repeatability. However, with manual preparation methods, it's inevitable that some operators simply have shakier hands or that some hit a mallet harder than others. At the end of the day, the samples get prepared, and it seems like the most important step.

What many people do not consider is that manual specimen preparation methods can contribute to variation in specimen quality. Naturally, the manual methods take a toll on the preparation equipment. Uneven pressure distribution and lack of protection of dies and blades lead to imperfections that mirror themselves in the specimens they are cutting. Though some of these imperfections may not be visible, even very small nicks can create stress concentrations in test specimens—especially for sensitive materials, such as films, foams and soft plastics. These stress concentrations can most obviously impact the specimen’s strain to failure, but arguably more importantly, can affect key results like modulus and yield.

So how can you mitigate this variation in your specimen preparation procedures? For any specimen preparation procedure, having a standard set of best practices is always recommended. But especially when there are multiple operators, or if turnover is high, a better option may be to use more automated preparation equipment. Instron CEAST hollow die punch machines (pictured above) apply even pressure to a specimen to ensure uniform stress distribution on the specimen, and maximum life of the blade. Dies are available for most common standardized tests, and custom dies are available upon request.

Instron CEAST milling equipment is ideal for consistent, low-volume preparation of hard plastics, composites and even some metal sheeting; notching equipment ensures accurate notch preparation for Charpy, Izod, and tensile impact tests.

For more information, take a look at our full suite of specimen preparation equipment here.

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