The measurements, tensile strength, yield strength and ductility, are calculated by the technician after the tensile test specimen has broken. The test specimen is put back together to measure the final length, then this measurement is compared to the pre-test or original length to obtain elongation. The original cross section measurement is also compared to the final cross section to obtain reduction in area. Elevated Temperature Tensile Testing is a proven method of evaluating the behavior of materials under a combination of heat and tension.
When performing an elevated temperature tensile test, the specimen is placed inside a furnace on our test carousel, which is capable of processing up to three specimens at a time. Our computer-controlled system heats the specimen to the required temperature, then allows it to soak. Next, the specimen is loaded into the test frame, where an extensometer in the latest design measures the strain on the specimen as the load is increased.
Watch how the test is performed. It is characterized by a sharp bend in the stress-strain curve at the end of the elastic region. Materials that exhibit no definitive end to the elastic region do not have a yield point. In those cases, yield is approximated by the offset method. However, it can only be determined experimentally by loading and unloading, gradually increasing stresses to find where plastic deformation begins. For materials that do not have a clear end to the initial linear region, the offset method is used to approximate yield.
The offset method uses the stress-strain curve of the material and overlays a line with a slope equal to the initial slope of the stress-strain curve.
The line is offset along the strain axis, usually by 0. The offset yield point is determined as the point of intersection between this line and the stress-strain curve.
The ultimate tensile strength is the maximum amount of stress a material can withstand before failure. This is the maximum value on the stress-strain curve. Tangent modulus is used to approximate the slope at a given point on the stress-strain curve.
The graph shows an exaggerated example. Refer to ASTM standards when selecting points for a tangent modulus. Chord modulus is used to approximate the slope between two specific points on the stress-strain curve.
Refer to ASTM standards when selecting points for a chord modulus. The secant modulus is used in its place as an approximation. Secant modulus takes the slope of a line which intersects the origin of the stress strain curve, and a point on the curve. This method is most useful for material comparison.
This graph shows an exaggerated example. Refer to ASTM standards when selecting points for a secant modulus. Generally speaking, to perform tension testing, you will need the following equipment:. The universal test machine frame provides the structure and rigidity needed to pull the sample apart at the desired rate. Tensile testing samples are usually materials of common industry standard.
When choosing a specimen, take note of the shape, size and dimensions, as well as the grips at the ends. These are important factors to consider before performing tensile testing. Avoid the possibility of the material fracturing in the gripped area. Any possible fractures should only occur within the gage length. Use a standard shape, and mark the cross-sectional area at the cylindrical test region to guarantee a fracture in the right place.
This way, the increasing tension will be focused within the gage length. The choice of grips and faces in the tensile test greatly contributes to the success of the test. If the equipment is incompatible with the specimen, the gripped area and the areas outside of the gage length will become prone to unexpected breakage or slippage. As much as possible, try not to let the tensile clamps damage the gripped area. It is also not a good idea to use serrated faces on tensile test samples that easily bend.
There is a decent array of grips and faces made available for specimens of all kinds. Two of the most common grips are the serrated grips and pinned grips. Do not forget to draw distance marks of regular intervals across the gage length. This will help determine the behavior of the sample throughout the tensile testing. Tensile testing machines are also known as universal testing machines. These machines hold your specimen with the use of grips or crossheads that firmly hold each end.
One grip keeps the material in place, while the other grip will pull until it eventually breaks. Tensile strength testers also come in different sizes and force capacities.
The variety serves to analyze other forms of measurement other than tensile tests. Privacy Policy. What is a Tensile Test? Ready to look at tensile test machines? Contact us to help you select the right machine. Contact Us Now! Tensile Test Machines Our tensile testers will measure characteristics such as ultimate tensile strength, yield strength, elongation, and modulus. Shop Tensile Test Frames. Get Your Questions Answered New to testing or know exactly what you want?
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