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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Interplas 2014 Preview: What’s the Cost to Your Reputation?

As one of the most trusted manufacturers of testing equipment for the plastics market, Instron has designed a tradeshow experience that takes you on a journey through the challenges (and occasional horrors) of plastics materials testing.

Visit us at Booth G12 for a cinematic experience like no other. In a truly theatrical setting, we will be depicting real-life customer stories, some of which could even occur in your lab. Don’t worry though; we guarantee there’s a happy ending to the horror story for everyone …

Visit Instron at Interplas – can you really afford not to? Read more

Looking for Ways to Keep Bent Test Specimens Securely Aligned?

 

Gripping bent specimens is challenging, but there are a few things you do. One, flatten the tabs with a small press prior to inserting into normal grip jaws meant for flat specimens. Two, use a combination of convex and concave grip jaws to eliminate the need to flatten the specimens. Three, use a set of dual side-acting grips that will basically flatten the ends when the grips are closed.

The third solution of using a set of dual-side acting grips requires that the grips have some kind of synchronization to ensure the grip faces close on center. This can be done several ways:

1.    Use traditional rack and pinion-type synchronizer mechanisms. These solutions are not very robust and are susceptible to excessive wear caused by hydraulic flow imbalances between the two pistons and piston load imbalances from bent specimens. Bent specimens are of particular concern because, although the specimen is initially straight, simply flattening the tab in one grip induces a bending of the specimen putting stress on the other grip mechanism.

2.    Hydraulic synchronization uses complex flow controls to ensure the proper amount of hydraulic fluid is ported to each piston so the grip faces close on center. These often require high-resolution position sensors and a flow control valve similar to a servo valve for each piston. This solution is expensive and prone to problems due to the complexity of the system.

3.    Instron’s DuraSync™ dual side-acting grips were designed to deal specifically with the kind of issues experienced when testing pipe sections that have not been flattened prior to installation into the grips.  The self-centering mechanical synchronizer is robust enough to deal with even major load imbalances with minimal wear and the grips incorporate an overload protection mechanism that prevents damage to the grips in unusual situations.  The adjustable clamping force alleviates specimen slippage and grip breaks. The DuraSync grips are also designed so wearable parts are readily accessible so the grips can be serviced in the field when needed. 

 

Find other helpful tips for overcoming challenges when testing the material properties of pipe & tube.

Find other helpful tips for overcoming challenges when testing the material properties of rebar.

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Concerned about Fatigue Specimens Overheating?

Fatigue testing of composite materials is becoming increasingly important as they find use in a wider range of critical structural applications with the expectation of long service life. It is now widely recognized that these materials do accumulate damage over long periods of cyclic loading, even if the failure mode and mechanisms are radically different to conventional metallic fatigue. One of the challenges, when performing fatigue tests on polymer composites, is to produce a good S-N curve in the shortest possible time without subjecting any specimens to excessive temperature generated by self-heating. Traditionally, the test frequency has to be set to a conservatively low value in order to ensure that overheating does not occur. 

 
In response to this, a new feature in WaveMatrix™ Software continuously monitors the specimen temperature and automatically adjusts the test frequency to minimize the test time and ensure that the specimen is never subject to an excessive temperature rise.

Read Dr. Peter Bailey’s interview with AZOM where he discusses this exciting new development. Read more

Being a Female Engineer at Instron

Mechanical Project Engineer Audrey Briodeau-Line speaks with the Women's Engineering Society about working at Instron in the male-dominated engineering industry. The article tells Audrey's story of working at Instron, beginning while at an engineering university in France. In discussing her career choices, she reveals the benefits of being a female engineer, especially in a company like Instron that provides assistance for women. Instron's Women's Business Network creates a community for female employees to have support in facing obstacles in the industry. Audrey Briodeau-Line's excitement and pride of being an engineer gives encouragement to other women interested in engineering.

Audrey Briodeau-Line

Read the full article at Women's Engineering Society. Read more

Instron at the World Congress of Biomechanics

From Sunday, July 6 to Friday, July 11, Instron will be at the World Congress of Biomechanics to discuss new technologies in the field of biomaterials. The World Congress of Biomechanics is an international event that showcases recent developments in the biomechanical industry every four years. Engineers, researchers, doctors, and academics meet to present new developments in their field. This year, the meeting is coming to the Hynes Convention Center in Boston, Massachusetts.

Come visit us at the charging station to hear about new developments in biomaterial characterization and tissue engineering. While testing implantable devices, tissue, and medical consumables with Instron technologies, innovators create modern advancements in the medical field.

On Thursday, take a break from the event to come and visit the Instron Worldwide Headquarters in Norwood, Massachusetts. We will provide lunch and transportation to visit our applications lab and manufacturing facility. While seeing the solutions for biomaterials Instron has to offer firsthand, meet Instron experts, including Anna Wynn, Business Development Manager for Instron TERM (Tissue Engineering and Regenerative Medicine).

Sign up for the tour here. Read more