Challenges of Rebar Testing

The following presentation provides an overview of recent changes and challenges facing rebar manufacturers, suppliers, and consumers when testing the properties of this durable material:

Challenges of Rebar Testing from Instron

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Composites on the Move

Composites are now a broad and well-established family of materials, but industry press releases frequently discuss “new and exciting” developments and opportunities. It should be remembered that there has been a commercial market in high performance, structural composites for well over 30 years, and European automotive manufacturers have made considerable use of lower performance glass fiber reinforced polyester (GFRP) bodywork since the 1950s.

Thermal image showing heating at failure
of a static tensile test (1mm/min)
of an impacted composite specimen

Furthermore, a high level of interest from the aerospace industry has resulted in a wide range of well-established static test methods giving reliable results. Sadly, there is still only limited consensus, so test houses and machine manufacturers find themselves maintaining an extensive catalog of fixtures in order to meet diverse international and industry standards. From this starting point, it might be argued that there is little news in composites testing, but in fact some exciting trends have started to develop.

Recently published in AM&P magazine, Peter Bailey, PhD - Sr. Applications Specialist - wrote an article on the growth in the dynamic testing market for composites.

We are including it here for you to download. Read more

Backward Strain at Yield — Discontinuous Yielding / YPE Material

During a recent customer visit, a concern was raised about a turnaround point on the graph that they had not previously seen. Following a bit of investigation, the customer was producing galvanized steel of various grades, some of which was aged. The graph below shows a magnified view of the fairly aggressive upper yield point (UYS or ReH), which results in an almost immediate drop in stress.

 

The customer had been testing galvanized steel for many years and had never seen negative strain at the yield point before. The new system, which was running Bluehill^® 3 with an AutoX, showed backward strain during yield, which proved surprising to the customer as it was not present in historical data. The AutoX was able to more accurately plot the reduction in strain (9 µm of movement) at yield due to its increased accuracy over the previous system.
 

The negative strain after upper yield is based on the way metals yield within a parallel section of material. Stress concentrations form at the shoulders or at the jaw faces in parallel specimens and typically propagate through the material at 45° angles. As the initial yielding takes place outside of the gauge length, which causes the stress (load) to drop, the gauge length contracts and a reduction of strain is seen on the graph. The video shows how the dislocations travel through the material, in this case from the bottom to the top of the specimen (12—24 seconds).

The diagram below shows how the extensometer arms are unable to see all of this extension.

 

 

To verify that the machine was operating correctly and the backward strain was a material characteristic, we used both larger and much smaller gauge lengths. The parallel length of the specimen was 65 mm, so a 60 mm and 10 mm gauge length was chosen for comparison. We found that when the 60 mm gauge length was used, no negative strain was observed. However, when the 10 mm gauge length was used, the negative strain dramatically increased in percentage.

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Does a Charpy or an Izod Impact Test Replicate any Real-Life Scenarios?

Q: Does a Charpy or an Izod impact test replicate any real-life scenarios by impacting the sample on a notched side (Izod) and an unnotched side (Charpy)?

A: The answer to this question is "No".

The Charpy and Izod impact tests are designed to evaluate the impact strength of materials under very well-defined conditions. They produce results that are comparative only and their impact configurations are not deliberately designed to replicate real-life scenarios.

The Charpy impact test is done in a three-point bend configuration, whereas the Izod impact test is done in a cantilever beam configuration. Therefore, the specimen is mounted differently in each set up.

Charpy Set Up

Izod Set Up

In the Izod impact test, the specimen is impacted on the notched side, whereas in a Charpy impact test the specimen is impacted on the unnotched side. However in both cases, the notch serves as the stress concentration zone and thus it is important to control the tip radius and notch depth to obtain reliable results.

Movement of a typical pendulum

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Reducing Variablity in Plastics Testing

Although you may be testing to specifications that would allow you to comply with international standards, many factors can cause variability in your plastics testing results. The following presentation provides a summary of the most common explanations for test data variability, including specimen alignment and method setup:

Plastics Testing: Reducing Variablity in Test Results 

If you would like to learn more about other challenges in plastics testing, read on.  

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Tissue Engineering and Regenerative Medicine is Changing the Game

Anna Wynn, Business Development Manager for Instron TERM (Tissue Engineering and Regenerative Medicine) discusses how this science can potentially provide a better quality of life for the population. Instron TERM systems produce 3D tissue comparable to native tissue, which can serve as a substitute or enhancement for tissue impaired by disease, injury, or age.

Read more as Anna reviews common challenges in the field and its growth potential. 

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Webinar Archive Hosts Recordings

Instron live webinars provide the opportunity to hear updates from experts on industry news and testing techniques. If you happen to miss the webinars, our library hosts the recordings:

Check back to watch the archive grow. Read more

Plastics Testing: Increasing Laboratory Efficiency & Throughput

The following presentation suggests ways that laboratories can operate more efficiently when testing plastics, including improving set up times and methods:

Plastics Testing: Increasing Laboratory Efficiency & Throughput from Instron

If you would like to learn more about other challenges in plastics testing, read on. 

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Instron's European Sales Director Discusses Rental Program

 

Tom Davies, European Sales Director, talks with AZoM about our contract rental program, piloted in the United Kingdom. The program offers the flexibility to rent Instron systems and accessories with no upfront investment. A rental can be issued on a monthly or a quarterly basis in order to try the latest equipment.

 

Since the program began last autumn in the UK., it has received significant interest and may be expanding to other countries.

Read more on this interview at AZoM.com.

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Sorting Over 15,000 lbs. of Food Donations? No problem.

Instron employees volunteered to organize over 15,000 lbs. of food donations, gathered with the help of the United States Postal Service Stamp-Out-Hunger Food Drive. After the rewarding work, the team was all smiles:

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Understanding Changes to Key Plastics Testing Standards

Are you aware of the recent changes to various international standards for plastics testing? This presentation provides a brief  summary:

Understanding Changes to Key Plastics Testing Standards 

If you would like to learn more about other challenges in plastics testing, such as variability and efficiency, read on.

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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