requirements. Because of the consistency in their design, there’s not much of a need to determine the material properties of the spring. They are not expected to break under tensile or compressive load applications because their design is intended to ensure a return to their original length, or free length. Material testing is more appropriately performed on the raw wire or metal samples, rather than performing the material calculations for the fully formed spring. In the case of springs, force testing often takes the form of testing an item’s functionality instead of its material properties. Take for example, the need to test a button or a switch. The manufactured parts typically have uniform designs, so the testing of a minimum required force rather than stresses across the component surface is simpler to perform. Other examples include syringes for both plunger testing and puncture testing, as well as packing material for strength – either for bubble wrap or air bag packaging to test for minimum popping force, or foam compositions for breaking strength under load. Material Testing Example – Wire Testing Building on the testing example of a spring, consider that the metal properties of the spring’s uncoiled wire can be assessed through the analysis of stress-strain testing. Unlike when in its coiled form, the lengthwise testing gives an easier means to determine the cross-section upon which the stresses are applied, which is equal to the area of the circle defined by the wire diameter.
Force and Material Test Applicability Checklist: Commonly Collected Information
Requirement
Force Test
Material Test
No (Material tests often require elongation measurements)
Does not require distance measurements
Yes (Often only collecting load values)
No (Extensometers are used for strain evaluation in Material Testing)
Requires Extensometers
Yes
Yes (this is a stress test and is a component of material testing)
Required Results include pressure values (PSI, MPa)
No
The L.S. Starrett company offers Uniaxial Force Testers and Material Testers designed for force application and data collection. However, there are different levels of controller software, depending on the requirements of the sample testing. The list above indicates a few parameters where the Starrett L3 controller software for Material Testing would be more convenient compared to the standard Starrett software suites, such as L1 or L2+.
The Long-Range Extensometer pictured here is the Starrett “MMS-EXT-1100M” on the Starrett Force MMS-5000-L3 material testing system, designed for Stress-Strain testing for samples up to 5000 newtons (1100 pounds) and up to 1100 mm (43 in) in total travel length.
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