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Tuesday, March 25, 2014

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.
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Monday, March 17, 2014

Changes Pipe & Tube Manufacturers and Suppliers Should Know

 
David Fry, Global Metals Market Manager, highlights recent changes in the market and what challenges should be anticipated.

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Friday, March 7, 2014

Charpy Impact Testing: Minimizing Hammer Changes


A common misconception within metals Charpy testing is that the specimen being tested must have an impact energy between 10% and 80% of the hammer capacity to be a standard compliant test. This is not true for metals tested to current common international standards such as ISO 148 and ASTM E23. This misconception sometimes comes from confusion with plastics standards (see ISO 179-1), other older metals standards (see GOST 9454-78), and historical use of a low resolution dial indicator on metals pendulum systems. Due to these misunderstandings, labs often have multiple systems or hammers for testing a range of specimen energies.

With the release of Instron’s latest MPX Motorized Pendulum Impact Testing System, we wanted to remove the need to swap hammers or have multiple systems in one lab. In order to achieve this, we had to address two areas: the resolution of the device and the method for changing hammer energies (weight).


The resolution of the latest encoder has been improved fourfold compared to the previous model. This enables the MPX to achieve a far lower resolution that had previously been possible with dial indicators or its digital predecessors. The MPX encoder delivers a resolution of 0.023J on a 450J system, this is compared to about 1-0.5J resolution on a dial indicator. This improved resolution translates to a usable limit down to 0.6 J to ASTM E23, the dial on the other hand has between 12.5J and 25J.

For more information, please visit our website.
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