The AutoX750 is a high-resolution, long-travel automatic contacting extensometer that can be mounted onto any electromechanical 3300, 5500, or 5900 table top and floor model systems. The AutoX communicates with the testing system through a USB connection and requires Bluehill® 3 Testing Software.
The AutoX can be used to measure strain and deflection in a wide range of applications. With a maximum travel of 750 mm and accuracy of ± 1 µm, the AutoX is capable of measuring high-elongation values in elastomers to small deflection measurements in rigid composites. The automatic control of gauge length and movement of the sensor arms provides customers with a faster, repeatable, and more reliable means of materials testing when compared with using traditional clip-on extensometers. Overall, the AutoX750 introduces an excellent solution for measuring strain and deflection in a wide range of material applications.
When testing composites in accordance to ASTM D3039, it is important to accurately measure strain throughout the test. Typically, with composite materials, strain values are relatively low due to the brittle nature of the specimens being tested. Thus, any inaccuracies in the measurement of strain will be magnified when testing composite materials. To ensure accurate data, it is important to use highly reliable and precise strain measurement devices.
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Composite tow specimens can prove difficult to test due to their geometry and delicate nature. As in many mechanical testing scenarios, measuring strain accurately is vital to ensuring correct results.
In addition to tensile and flexural testing, another common form of determining the material properties of plastic (both unreinforced and reinforced) is compression testing. This test is useful for determining the modulus of elasticity, yield stress, compressive strength, and the deformation beyond yield point. The method by which the compression test shall be conducted is defined in ASTM D695.
ASTM E8 describes tension testing methods to determine yield strength, yield point elongation, tensile strength, elongation, and reduction of area of metal products. It applies to metallic materials in any form, including: sheet, plate, wire, rod, bar, pipe, and tube. For each of these specimen types, the standard defines suitable geometries and dimensions, requiring specific gripping solutions that are critical to performing a successful test.
This European standard was introduced in September 2009, and replaces the withdrawn EN 10002-1:2001 standard. It specifies the method for tensile testing of metallic materials and defines the mechanical properties which can be determined at ambient temperature. The test involves straining a test piece in tension, generally to fracture, for the purpose of determining one or more mechanical properties.
Products that may be tested in accordance with this standard include metallic sheets and plates, wire, bar or section, and also tubes. Specimens are gripped to ensure that the specimen is aligned axially in order to minimize bending. The specimen is then strained in tension until failure, and load and strain data are recorded.
The standard provides for two methods, one uses strain rate control to minimize the variation of strain rates during the determination of strain rate sensitive parameters, and the second method's testing rate is based on the stress rate. The choice of method and rates are at the discretion of the test laboratory, but must be clearly stated when reporting test results.
The standard also includes recommendations for specimen types and dimensions, advice concerning the use of computer-controlled tensile testing machines, and methods for estimating the uncertainty of measurement. Results determined typically include yield and proof strengths, ultimate tensile strength, and elongation at fracture.
Plastics tensile standards, such as ASTM D638 and ISO 527-2, cover a range of plastics including thermosets, thermoplastics, and fiber-reinforced plastics. Test specimens may be rigid, semi-rigid, molded or extruded plastics, and are commonly in the shape of a dumbbell or dogbone.
The mechanical properties of plastics vary depending on the type of plastic, as well as the additives that may be incorporated into the formulation. Properties, such as strength, ductility and toughness, are influenced by different types of additives. To determine the appropriate testing equipment, it is important to understand how material behavior changes as a result of the various additives.
Selecting the appropriate extensometer can be a difficult task when interested in measuring both modulus and strain to failure. For some types of extensometers, such as a static clip-on extensometer, accuracy is a function of the amount of extensometer travel. The more travel an extensometer is capable of performing, the lower the accuracy. This makes it difficult to measure both modulus and strain to failure for plastics that have relatively high strain. Since the standard requires direct strain measurement only up until the yield point, static clip-on extensometers are suitable for the determination of elastic modulus.
ISO 178 investigates the flexural behavior of plastics to determine the flexural strength, flexural modulus, and other aspects of the flexural stress/strain relationship.
This ISO 178 test method is suitable for use with extruded plastics, including filled and unfilled types, rigid thermoplastic sheets and thermoset molded plastics, including filled and reinforced compounds.
Both three-point and four-point loading flexure fixtures are used to evaluate these materials. Deflectometers or other strain measuring devices, such as an extensometer or LVDT have historically been required for direct flexure measurement when conducting four point loading tests. Direct strain measurement devices were not a requirement for three-point loading tests until the 2010 release of ISO178.
The support span requirement is based on a ratio of the specimen thickness. It is important to know the range of sample dimensions before selecting a fixture. Loading and support anvil dimensions may differ on specimen thickness.
Usually medical catheters are inserted into canals, vessels, passageways, or body cavities to inject or remove fluids from the body. More broadly, medical tubing can be associated with catheters or extended to external devices such as dialysis machines, feeding tubes, and intravenous (IV) therapy drips. Failure of these devices could result in severe patient injury. As a result, mechanical testing is a critical requirement to demonstrate device safety. In all testing applications, correct gripping is essential for obtaining accurate measurements.
Correct gripping of a medical catheter is a delicate balance between holding the material in place while avoiding premature specimen damage. Depending on the specimen, we recommend using pneumatic side-action grips with rubber-coated faces or pneumatic cord and yarn grips. For instances where tubing is more rigid, the pneumatic side-action grips are more appropriate. Conversely, for ductile catheters and tubing, we recommend using the cord and yarn grips. This will ensure secure fixture of your specimen while providing the user with control over air pressure.
For a similar reason, choosing an appropriate extensometer to accurately measure strain is critical.
Nitinol is a shape memory, super-elastic alloy for which the biomedical industry has found extensive uses. A few examples include stents, dental wires, catheter guide wires, internal fracture fixation devices, and biopsy forceps. The major challenge in testing Nitinol is attaining accurate strain measurements. The crosshead position or LVDT reading does not provide the accuracy necessary to achieve specific strain criteria specified in ASTM standards. A clip-on extensometer is often used, yet may cause bending of the wire causing premature failure. Additionally, most clip-on extensometers have insufficient gauge lengths to accurately characterize the material.
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