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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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

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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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

Instron Recognizes Young Scientists in Darmstadt

Darmstadt has served as a center of expertise in structural durability for over a century. The Symposium on Structural Durability in Darmstadt (SoSDiD) provides a forum to present the current state of this work to the national and international fatigue community.
 

Research shared at the Symposium came from across the globe. The topics highlighted this year revolved around welded and bolted joints, effects of corrosion, thermomechanical and low cycle fatigue, lightweight design as well as fatigue testing.

As in previous years, Instron awarded scientific studies in the field of fatigue related research. This year a group of four young scientists from Darmstadt were awarded for their work on "Fatigue Assessment of Weld Ends".

 

Dr.-Ing. Matthias Kaffenberger; M.Sc. Ehsan Shams; Dipl.-Ing. Ina Platte; Erik Schmidt-Staubach; and M.Sc. Franziska Strobel

(Image Source: Fraunhofer LBF | Artist: Claus Borgenheimer)

We would like to congratulate them on their well deserved awards and wish them all the best for their future in fatigue-related work. Read more

4-Point Bend Testing of Carbon Fiber

Carbon fiber is an extremely strong material. Depending on the manufacturing process, this textile can have typical modulus values of about 138 Gpa and ultimate tensile strengths of about 3.5 Gpa. Industry professionals can find themselves seeking to replace traditional steel components with lighter carbon fiber counterparts to achieve a much higher stiffness to weight ratio. To determine the appropriate thickness for the corresponding carbon component, one must undergo some experimental validation.

 In a recent test, an ElectroPuls E3000 was fitted with a 5kN Dynacell™ load cell and a 4-point bend fixture. Once aligned, the upper and lower spans of the 4-point bend fixture were set to 30mm and 100mm respectively. For this sample, a cyclic load-controlled test was conducted with a mean load of 110N of compression and an R value of 0.1 (equivalent to a 90N amplitude). The cyclic loading was carried out at 10Hz for 2 million cycles, which was expected to last around 55 hours. The maximum deflection of the carbon fiber specimen was collected for every 1000 cycles with WaveMatrix™ software.

All ElectroPuls systems are fitted with an optical encoder for precise extension control. This allows for accurate displacement measurement readings of the carbon fiber specimen of up to one micron of a millimeter over the course of the entire 2 million cycles. The resultant displacement of the carbon fiber specimen is acquired by the 8800 controller at a rate of up to 5kHz. WaveMatrix™ software conveniently allows users to specify exactly which data is saved and at what frequency. For this test, a higher data acquisition rate was used during the first few hundred cycles. Thereafter, every 1000 cycles was recorded and exported in the form of an easy to read Microsoft Excel file. From this, researchers can then determine the overall changes in displacement of the carbon fiber over the entire 2 million cycles, and whether or not the material properties of the specimen suit a particular application. Read more

Software Module Increases Test Frequency for Fatigue Testing of Composites and Polymers

Senior Applications Specialist for Dynamic Systems, Peter Bailey shares with AZoM how the Specimen Self-Heating Control (SSHC) module to WaveMatrix™ Materials Testing Software can enhance fatigue testing of composites and polymers.

SSHC optimizes test frequency by maintaining consistent specimen temperature and reducing energy with shorter test durations, promoting increased throughput and consistency.

Visit AZoM to view the full article.

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What is the Best Way to Check the Functionality of my ElectroPuls™ Load Cell?

Instron load cells are robust and built to last. Therefore, checking the load cell’s functionality on a daily basis is not usually necessary unless you suspect a real problem. That being said, it is always a good idea to be safe than sorry!

To safely assess the functionality of your load cell, you can simply place or hang a known mass from the load cell to verify that the actual reading corresponds to the value of the mass. A mass of 20Kg or more is usually the safest bet for an ElectroPuls E1000 and  E3000. You can always contact Instron support if you suspect you are having issues with your load cell. Remember: make sure you set appropriate limits whenever conducting any kind of test or load cell reading! Read more

Energy-controlled Impulse Testing of Shoes

Shoe and shoe material manufacturers alike must be able to prove that their products will withstand a substantial amount of wear and tear before releasing them to market. Useful in this analysis is the ability to simulate the impact of a runner on the sole of a shoe. During a typical gait cycle, these impacts can be higher than 3kN for an adult runner. In addition to controlling the load with which an impact is generated, researchers may also wish to control the energy which is generated as a result of the impact. A testing machine, which can successfully cater to these requirements, must be able to create and maintain a repeatable impact of a certain energy over a prolonged number of cycles.

Custom waveforms were created to replicate the impact of actual gait cycles. WaveMatrix™  software allows users to create and import their own custom waveform in the form of a CSV file, achievable in Microsoft® Excel. Through this custom waveform tab, customers also have the ability to specify a very precise impact duration. The up-to-5kHz acquisition rate of the 8800 Controller enables the waveform to be precisely controlled in the magnitude of milliseconds. As materials testing machines usually have two main controllable transducers, Instron established a method for achieving the given energy requirement for each impulse. The Advanced Amplitude Control is a feature of WaveMatrix that is key to conducting energy-controlled impulses, using a combination of controller gains to make sure that the energy requirement is met for each iteration of the impulse. The combination of this feature, in conjunction with the Calculations Module, allows the ElectroPuls™ to test footwear based on constant load, energy or any other requirement included in the calculations portion of WaveMatrix. Read more