In order to check how well a product meets the requirements and to choose the right supplier, it is of vital importance to be aware of rules and peculiarities of mechanical tests when you run them. Here are a few guidelines which will help you to test steel strap successfully and to avoid mistakes during initial testing.
What is the gist of a steel strap test?
In the course of testing, the sample strap is subjected to deformation by stretching till it breaks. During the test product mechanical properties are determined, along with monitoring such characteristics as break strength and elongation. The test should be conducted in properly equipped rooms or laboratories at the ambient temperature of 10°C to 35°C.
Testing sample: shape and length
Normally, the shape and length of the testing samples depend on the shape and size of the product to be tested. Sometimes, the samples are specially prepared by mechanical finishing. However, in accordance with the manufacturing standards, the samples of steel packing strap should correlate with the strap width, while not exceeding 300 mm in length. For illustration, let us consider strap tested by the Specification (the gauge length of the sample: 100 mm), which is fully consistent with EN 13246 Testing Methods.
The total length of the test sample should be about 300 mm, but not less than 203 mm. This length is determined by the gauge length of the sample (100 mm), as this length is required to fix the sample in the testing device (the grips of a tensile machine). Each sample should be marked with a thin line or match mark by a marking machine or a ruler in 10 mm increment. It is critical to take a sample free of any cuts that may lead to unexpected fracture of the sample at the stress concentrator.
The correct way to place a strap sample in the testing machine
Once we have determined the shape and size of the sample, it is crucial to place it properly into the testing machine. Please make sure that the gauge length of the sample is located in the middle in between the grips. The strap sample should be fixed true vertically, so that the applied tensile force matched the sample axis.
It is required to use the proper fixing tools to minimize the sample slippage or fracture at the grips. If any break occurs at the grips or within 25 mm from them, the test should be repeated.
The strap sample is ruptured: what’s next?
Upon completion of the test, when the sample is ruptured, it is required to measure relative elongation. The relative elongation is the finite increase of the sample length resulted from the tensile strength test. How to calculate it?
After the rupture, remove out of the grips both parts of the sample, place them on an even surface and precisely fit together along the fractured line. Using a precise ruler or a caliper, measure the distance between the thin lines or match marks.
Then, calculate the relative elongation which is determined by formula:
minus the initial gauge length of the sample (100 mm),
divided by the length prior to the test, and multiplied by 100.
Special precautions shall be taken to ensure proper contact between the parts of the ruptured sample during the measurement of the final working length of the sample. This is critical for testing steel packing straps with a slight elongation.
Following these simple recommendations will help you to avoid pitfalls, while testing packing products, and to choose the right strap which would be optimal for your product.