When Procuring A Stress Tester

By Author: Vishal Khosla
Total Articles: 19
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Stress tester is used to test the ability of a material to withstand progressive and localized structural damage when it is subjected to cyclic loading. Microscopic cracks begin to form at the surface and when these meet a certain size, the structure fractures.

Industries require testing instrumentation that enables them to quickly deliver realistic and complex testing, allowing them to identify potential performance problems that may have a negative impact on the bottom line of the company.

Robust design, high end electronics and easy to use software are some of the basic features they expect in the instruments whether it is stress tester, multi-functional tribometer, indentation and scratch tester, profilometer, AFM, polishers, coating and deposition.

Let us ponder over stress tester as a case study to see how a manufacturer will approach it for a purchase. It is used to test the ability of a material to withstand progressive and localized structural damage that occurs when a material is subjected to cyclic loading. A material suffers fatigue when it is subjected to repeated loading and unloading that ...
... is above a certain threshold. Microscopic cracks begin to form at the stress concentrators, grain interfaces and persistent slip bands. When the crack meets a critical size, the structure will suddenly fracture.

Shape of the structure does affect the fatigue life. Sharp corners or square holes lead to elevated local stresses where fatigue cracks can begin. For increasing the fatigue strength of the structure, round holes and smooth transitions or fillets are important. Factors that affect fatigue-life are cyclic stress state, material type, surface quality, geometry, size and distribution of internal defects, residual stresses, grain size, crack closure, temperature and environment.

A procurer would prefer a stress tester that can quickly calculate residual stress of thin and thick films.

They would look for an instrument that has 2D and 3D maps, Both point and array lasers, and Unique optical flat referencing.

A stress tester of a top supplier measures residual stress by using non-contact lasers. It precisely determines radius of curvature of the sample. Depending on accuracy and application, there is a broad choice of lasers. Multiple lasers can be used on the same platform.

Residual stress can be evaluated using instrumented indentation technique. The tester can measure quantitative values for residual stress if it comprehends the relationship between the load gap and residual stress. When tensile or compressive residual stress is applied, the load-depth curve shifts to right or left side.

One of the stress tester models allows users perform quick and easy tests with wireless communication module between the main body of the instrument and the computer attached. Superposition of the obtained curves allows changes in residual stress to be analyzed immediately.

3D imaging is another essential that the manufacturers expect in a stress tester. Automatic XY stage and vision software allows creation of 3D imaging of the scanned sample. Presence of temperature and humidity chambers allows to measure effect of temperature on the stress.

Specs in a top-notch stress tester may include Repeatability up to 0.001um, 2D Line and 3D Map data display and stress sensitivity of 0.4 MPa. The instrument is used in industries like semiconductor, electroplating, PVD, DLC, CVD, ALD, MEMS, decorative coatings, solar cells, hard coating, protective coating, thermal spray, paint, etc.

Author of this article is associated with Rtec Instruments, a California based company that deals in stress tester, surface profiler, high temperature tribology instrument, nano indentation, and other instruments.