Testing Uncovers Titanic Mystery

In light of the 100 year anniversary of the Titanic this weekend, we're sharing a story found on ABCNews.com.

The Unsinkable Ship sank in less than 3 hours back in 1912. Did the Titanic sink simply due to the impact of an iceberg and the speed of the ship or was it a malfunction in the mechanical property of a key material holding the ship together?

A recent study, conducted by Tim Foecke of the National Institute of Standards and Technology and his colleagues, tested the rivets of the ship's hull; rivets that were made of wrought iron, not steel like the rest of the ship's rivets. The one big difference: wrought iron tends to soften at lower temperatures. 

Using a static hydraulic universal testing system, Foecke and colleagues simulated the ship's design with 2 pieces of 1-inch thick steel plates held together with wrought-iron rivets. Through a compression test, they were able to simulate the force on the rivets and found that the rivet heads broke off, proving their substandard quality. As the rivet heads popped, the steel plates separated, allowing water to pour into the ship's hull at a very fast rate.

"If the wrought iron rivets were up to standards, they would have been fine," says Foecke. "But since there was no method for quality checking, the rivets used on the Titanic were not up to standards, which caused them to fail prematurely."


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Doing Their Part to Ensure Safety on the Playing Field

We were approached by several visitors at NPE whose companies were interested in learning more about impact testing of helmets as it relates to increased safety. Many of us that are sports enthusiasts are reading more and more about concussions and the potentially devastating effects they can have on athletes as they occur on the field – and their long-lasting effects later on in life. There is a growing urgency to enhance the safety of athletes – especially in football and hockey.

Not only are our customers focusing on safety, I found this interesting article about two high school althetes who, after witnessing a sports-related injury, decided to enter the Rhode Island Science & Engineering Fair with their findings on impact testing of head gear. I won't spoil their results, but I will mention that they went on to receive blue ribbons for their project! Read more

Fatigue Testing of Stents and Stent Materials

It seems we've been focusing a lot on the medical and biomaterials markets lately, but it's an industry that is growing with new techniques, standards, and more.

Traditional fatigue testing of complete stent devices is addressed by ASTM F2477 “Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents”, which specifies methods for fatigue of complete devices through hydrodynamic pulsation. The method involves placing complete devices into mock arteries and subjecting them to 400 million cycles of internal pressure pulsation (10 years of human heartbeats), forcing them to radially expand and contract in each cycle. The test can either be performed between pressure limits, simulating diastolic and systolic pressures; or displacement controlled, reproducing the minimum and maximum diameters that a stent would see in vivo under worse case conditions. Tests are typically performed at frequencies of up to 50 cycles per second, resulting in typical test durations in the three to six month range.

The acceptance criterion of devices is a simple pass/fail one, in that no fracture of the stent can occur during these in vitro tests for success. Many devices from varying manufacturers have undergone Pre-Market Approval (PMA) by Food Drug Administration (FDA) and have gone into clinical use. Although this traditional “Test to Success” approach of fatigue testing has not resulted in failures, the reality is that many of
these devices are fracturing in vivo.

In early 2006, the FDA and ASTM started looking at ways that could eventually improve the current durability assessment of cardiovascular devices. Initially, two working groups under the ASTM F04.30.06 Endovascular Devices Task Group were established; the first group concentrates on better understanding of the physiological conditions devices undergo in vivo and transferring this knowledge into boundary conditions for use in testing, evaluation and modelling. The second group, entitled “Fatigue to Fracture” (FtF) group, was charged with developing alternative and improved test methods for fatigue testing of cardiovascular devices.

An alternative method that is being rapidly adopted is a “Fatigue to Fracture” approach. A rudimentary technique that is more akin to aerospace testing, this methodology involves a combination of FEA modelling and in vitro testing to assess the durability of stents through established fracture mechanics techniques. These testing guidelines and standards are still under development. Several testing techniques have been developed recently that provide testing results that provide support as manufacturers submit products for regulatory approval.

To enable a representative sample of specimens to be evaluated and to reduce overall test time, multiple samples must be tested. The multi-specimen fixtures assist cardiovascular implant manufacturers to assess these long-term fatigue characteristics of nickel-titanium (Nitinol), CoCr, stainless-steel, and other stent materials and structures. It is important that each specimen station feature a fatigue-rated load cell, precision alignment adjustment, and applicable grips for the material or structure undergoing test. The specimens should be tested in vitro at body temperatures and results should include trend monitoring of forces to determine each specimen fracture. Read more

What's the Buzz from Orlando?

With NPE well underway in sunny Orlando, FL, we've heard from our colleagues in the booth about the excitement and energy that's filling the 920,000 square feet of exhibiting space. Also, one note of surprise is that a lot of the attendees who stop by the booth are not aware that CEAST products are a valuable part of the Instron line.

"It's been interesting for me to see that there are still some customers in the materials testing industry who do not know that Instron offers a full range of plastics solutions," says Marco Bronzoni, CEAST Marketing Manager, Italy. "This is a great chance for all of us in the booth to talk about the integration of CEAST with Instron and how we offer systems for rheology, melt flow, thermal-mechanical, and  specimen preparation."

With that being said, it seems the systems we're exhibiting in the booth meet the expectations of the attendees at the show.

If you're in the Orlando area - or already at NPE - stop by the Instron booth (#2403) to meet Marco and take a look at the systems in action! Read more

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

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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