Quick Tip: Determining if a Specimen is Too Heavy for Your Test

Q: I have a 1 kN load cell. How do I determine if a specimen would be too heavy for my tensile and compression tests?

A: To be cautious, always use mechanical limits to ensure that grips or platens aren’t compressed onto each other. The specimen weight is not often an issue, but if you're using our load cells, they incorporate several overload prevention features. When combined, the weight of the upper grip and the expected maximum load during testing should be less than one-and-a-half times the load cell capacity. In this case, 1.5 kN. Read more

When is Fatigue Not a Weakness?

As a materials testing company everyone at Instron usually sees fatigue as a weakness, but 3 Engineers from our UK office actively seek out fatigue for thrills on the weekends.

These 3 mad mountain bikers are going to fatigue test their own bodies over a gruelling 200 km (160 miles) off-road course to raise money for a very deserving local charity.



Last weekend's warm-up ride ...

The Iain Rennie Grove House Hospice Care charity provides palliative and respite care for terminally ill patients in the hospice center itself or in the comfort of their own home. Started 25 years ago for a young sports-mad engineer, just like our 3, the Iain Rennie Hospice has provided much-needed care and support 24 hours a day 365 days a year to 10,000 patients and their families in the local area! The nurses and staff providing this support don’t give into fatigue easily and nor will our boys!

The ride will take our team across wild (and since it is the UK probably wet) terrain - a test of physical and mental endurance taking our brave riders far beyond their usual limits. Our plucky team is looking forward to the long hill climbs, steep descents, have vowed to laugh in the face of metrological adversity (wind, rain, and freezing temperatures to you and me), and of course to endure the inevitable saddle sores armed only with a tube of antiseptic and a smile.

Our 3 mountain bikers have shown their creative side in raising money for the charity as well. They will be riding in their very own Instron Cycling Team cycling jerseys. They’ve sold 45 jerseys to other Instron colleagues, so look out next time you are on the trail!

We are hoping that, unlike most specimens we test, these charity-supporting bikers will not have a point of failure and that all 3 of them successfully complete the ride, fatigued, but definitely not weak!

Related Videos and Testing Solutions
Watch this video on fatigue testing the sole of a sneaker
Putting Athletic Footwear to the test

Read more

Are You a Statistic?

According to the Center for Disease Control and Prevention, motor vehicle crashes are the leading cause of death in the US among people ages 5-34. About 6,400 adults are injured in motor vehicle accidents every day. Still, nearly 15% of us don’t buckle up for every trip we take in our cars.

Without a doubt, one of the most effective ways to reduce injury and save lives in vehicular accidents is by wearing a seat belt. Seat belt material, also called webbing, is usually made from polyester. The polyester fibers are uniquely woven so that they stretch when pulled which helps absorb energy from a crash, making the impact less severe for the occupant.

So, just how strong are seat belts? Check out this video we performed in our Applications Lab. This seat belt material broke at roughly 30 kN; that’s about 6,750 lbf ... enough to give me peace of mind on my ride home today! Read more

Industry Update: Mechanical Testing of Stents and Stent Materials

Stents are a wonderful creation of modern medical engineering that aid physicians and surgeons in the treatment of heart disease. Conditions, such as smoking, diabetes, and high cholesterol help promote atherosclerosis, the build up of fatty plaque within arteries, which can ultimately lead to heart attack and stroke.

We have found that more recently smart materials, such as Nitinol (Nickel Titanium Alloy), have been used by stent manufacturers in the production of stents. Nitinol exhibits both shape memory and super-elastic properties, making it perform particularly well when used for self-expanding stents. Nitinol stents are slightly larger than the size of the intended artery, and after deployment they exhibit a chronic radial force to maintain position.

With stringent requirements from regulations, manufacturers must demonstrate that they have considered risks of device failure and satisfactorily mitigated against them. Mechanical testing of stent and stent materials is performed in vitro to aide designers and researchers in gathering performance data ahead of device approval and clinical use. Although mechanical testing does not begin to simulate the complete in vivo conditions that devices undergo, it does allow experimental validation and provides more accurate data for Finite Element Analysis (FEA) and computer modeling of cardiovascular devices.

Although stents have proven to be effective and important devices for the medical device community and the general patient population, they continue to evolve. Larger and smaller stents designed for peripheral networks in distal extremities - like the superficial arteries, carotid arteries, and neural pathways - test the limits of existing materials and testing technology. Continued material evaluation, development, and delivery of new testing methods are important for the evolution and success of these devices.

Additional articles you may find interesting:
Mechanical Testing of Medical Implants (free whitepaper download)
Stent Testing Solutions (video)
Radial Force Evaluation of Stent Grafts Read more

What is 21 CFR Part 11 and How Does it Affect Me?

Have you heard of 21 CFR Part 11? If not, it is a set of compliance requirements that allow for safe and secure storage and submission of electronic records for industries regulated by the US FDA. In other words, this is the FDAs procedure for quality control of electronic data. Any company storing electronic data that could be audited by the FDA must comply with this set of requirements. Although the FDA still permits paper-based data storage and submission, this approach can lead to higher costs, increased time to market, decreased quality, and challenges with information storage availability, retrieval and portability, as compared with electronic methods.

But don't worry; there are two ways to approach this requirement:

Partial Electronics - this approach stores the electronic records as equivalent to paper records with handwritten signatures. It still requires a large amount of printed documentation that carries the same risks & challenges as a full-paper approach.

Electronic - this approach uses all electronic records and electronic signatures, so no paper documentation is necessary. This approach is less subject to human error and can save significant time and money with automation of processes. Additionally, a completely electronic approach allows for electronic submission of data and reports to the FDA, which can save additional time and costs to the organization.

Do you find information like this helpful? What other questions do you have that we can help answer? Read more

Quick Tip on Gripping

Q. I find it rather difficult to avoid torsion when gripping flexible specimen like paper. Any tips?

A: Depending on the style of grips, torsion should not be an issue. To minimize the torsion, ensure proper alignment of the grips. Bringing the upper and lower grips closer together will allow you to determine if they are properly aligned. Since clamping thin, flexible specimens can be awkward, I find that closing the specimen in the upper grip first allows me to put a slight tension on the specimen; this helps ensure it will be evenly loaded while closing the lower grip.

Have more gripping questions? Leave me a comment below. Read more

Question from a Customer

Q. What is the resolution and accuracy of your Smart Rheo load cell?

A. The CEAST Smart Rheo load cells resolution is 0.05% of full-scale and the accuracy is 0.5% of full-scale. For example, the 20 kN load cell has a resolution of 10 N and an accuracy of 100 N.

Read more

Hobas Pipe USA Installs Giant Custom-Built Instron Frame

HOBAS® Pipe USA, a producer and supplier of fiberglass-reinforced polymer mortar pipe systems, produces pipe and pipecoupling products in a wide range of sizes. Worldwide population growth has increased the demand for bigger water supply and sewage pipes. Consequently, the pipe diameter range was set to increase beyond the size capability of their current testing equipment. They needed a system that could test their full range of products and they turned to Instron for the solution. The resulting testing system was so big that it was installed out in the open and the test building was constructed around the frame.

HOBAS pipes are centrifugally cast, glass-fiber-reinforced, polymer mortar (CCFRPM) construction. A feeder arm places materials in multiple layers, building up the wall cross-section. A computer controls and monitors the layer formation and thus the formation of the varying layers of the pipe.

The resulting product has multiple layers including reinforced outer and inner glass layers. The actual cross-section is of a highly engineered composition with transition layers to optimize pipe performance. Other centrifugal casting processes exist, but the HOBAS process is truly unique. By adjusting the quantity, placement, and orientation of the glass-fiber reinforcements, HOBAS can specifically tailor their products for a wide range of environmental demands and service requirements.

HOBAS has stringent quality-control testing requirements for their products and this type of construction presents complex testing challenges. Many different tests are performed such as pipe stiffness, compression and tension testing, and corrosion resistance. The main flexural, tensile, and compressive testing is performed to the following ASTM standards:

• D2412 - Standard Test Method for Determination of External Loading Characteristics of Plastic Pipe by Parallel-Plate Loading
• D638 - Standard Test Method for Tensile Properties of Plastics
• D695 - Standard Test Method for Compressive Properties of Rigid Plastics

HOBAS Pipe’s current testing equipment had become limited by size. The maximum pipe diameter that they could test was 110 inches. They were planning to manufacture 120-inch diameter pipe for a major new sewage replacement project in Houston and knew that the future demand for larger pipes would grow. They needed a new tensile/compressive testing system.

For their new system, they specified a test height requirement of 160 inches to allow for future, even larger pipe dimensions. Working with Instron sales engineers, HOBAS determined that a custom-built Model 5989 load frame with Bluehill® Software suited their purpose perfectly.

The sheer size of the new system allowed for two alternative installations; either lower the equipment through the roof of the existing building or install the load frame in the open and then construct a new building around it. Both schemes had advantages and disadvantages, but in the end the HOBAS project team decided to take the latter route. The new building incorporates a sub-floor that is so deep the frame table is level with the main floor and the pipe sections are rolled into position for testing.

Construction was recently completed and the load frame was tested and commissioned into service.

When asked why HOBAS decided to purchase an Instron system, Kimberly Paggioli, Vice President of Marketing and Quality Control for HOBAS Pipe USA, responded, “Two main reasons. Familiarity; a sister company already has experience with Instron equipment, and locality; you have field service engineers close at hand.” Read more

Selecting a Pressure Transducer for Your Capillary Rheometer

It is common to refer to pressure transducers by their full-scale range in megapascals (1 MPa is 145 psi). The accuracy is 0.25% of the full scale of the pressure transducer. To obtain the highest quality data, the recommended minimum pressure is about 10 times the accuracy and the recommended maximum pressure is about 90% of the full-scale range. For example, if you select a 1,000 bar transducer, referred to as a 100 MPa transducer, the recommended minimum is 2.5 MPa (362 psi) (ten times the accuracy) and the recommended maximum is 90 MPa (13,050 psi) (90% of full-scale range).

Individual capillary rheometer pressure transducers have a limited range. For example, a 15 mm diameter barrel can only apply about 35.5 kN before it reaches the maximum of 200 MPa. Multiple transducers are often used to cover a wide variety of samples and tests.

Read more

A Very Deep Investment

The challenges of testing Fiber Reinforced Concrete (FRC) go well beyond what we would normally think of with respect to concrete testing. The difference lies in the fact that most of the valuable information from an FRC test comes after the concrete fails. The ability of FRC to resist crack growth after the initial crack is determined by measuring the toughness (typically area under the curve) of the sample as it is deflected well past the first crack. All of these tests must be run under servo-control and one of the more common tests must be run using the measured beam deflection as the servo feedback. This can be very challenging as the specimen goes from being very stiff to very compliant after the first crack.

FRC is one of the fastest growing segments in the concrete industry as more and more engineers, architects, owners, specifiers, and concrete contractors are turning to the use of fibers to supply their reinforcing needs in their concrete applications. In many cases, fibers are replacing traditional rebar. Although still a small part of overall concrete production, some estimates have the North American market growing at 20% annually.

A US-based company is currently in the "Pre-Feasability" phase of excavating a copper mine where they are boring a shaft vertically to a depth of nearly 7000 ft (2100 m). Once they get to this depth they will bore horizontal shafts under the copper deposit and mine the ore from beneath. They do not expect to start producing ore until 2020. Talk about a long-term investment!

As they bore the shaft it is being lined with Shotcrete, which is basically a fiber reinforced concrete product that is shot out of a tube onto the walls of the shaft.  As they apply the Shotcrete they also make 3 beam samples for testing to ASTM C1609. The samples are placed in a climate-controlled storage area until they are about 12 hrs old and ready for testing. The samples are then tested on the custom 300 KN testing system to determine the strength and toughness of the concrete. If the results indicate adequate strength they can allow people to re-enter the shaft to continue excavating. If not, they must tear the old shotcrete down and re-apply. The time requirements and critical nature of the testing make it impossible for them to use a test lab.

As this was our first experience with FRC testing, we had a steep learning curve with respect to how the specimens react. The test standards certainly do not tell the whole story here. Our biggest challenge came on the ASTM C1609 test, which is a Third Point beam loading of a 150 x 150 x 450 mm (6 x 6 x 18) in sample. During the test, deflection of the sample is measured using 2 LVDT's fixtured to the specimen; one on either side of the specimen to get the average deflection.

The ASTM standard requires the machine to be in servo-control using the LVDT's as feedback to maintain a deflection rate of approximately 0.05 mm/min (0.002 in/min). This is already looking challenging. But wait, there are more challenges. Unlike a typical concrete beam test that ends after the concrete cracks, this test must run well past the initial crack and maintain the same deflection control mode. The testing machine must be able to maintain servo-control through the large deflection change that occurs during the initial crack and it must also accommodate the very large change in specimen compliance that occurs when the concrete fails and the fibers begin to take load.

Potential projects suited to the use of fiber reinforced concrete:

• Residential: driveways, sidewalks, pool construction with shotcrete, basements, colored concrete, foundations, and drainage
• Commercial: exterior and interior floors, slabs and parking areas, and roadways
• Warehouse / Industrial: light to heavy duty loaded floors and roadways
• Highways / Roadways / Bridges: conventional concrete paving, SCC, white-toppings, barrier rails, curb and gutter work, pervious concrete, and sound attenuation barriers
• Ports and Airports: runways, taxiways, aprons, seawalls, dock areas, and parking and loading ramps
• Waterways: dams, lock structures, channel linings, ditches, and storm-water structures
• Mining and Tunneling: precast segments and schotcrete, which may include tunnel lining, shafts, slope stabilization, and sewer work
• Elevated Decks: commercial and industrial composite metal deck construction and elevated formwork at airports, commercial buildings, and shopping centers
• Agriculture: farm and animal storage structures, walls, silos, and paving
• Precast Concrete and Products: architectural panels, tilt-up construction, walls, fencing, septic tanks, burial vaults, grease trap structures, and bank vaults and sculptures

Read more