Grip Solution for Testing Polymer Hydrogels
Due to the composition of polymer hydrogels, gripping and loading for the testing of mechanical properties can be difficult without the proper equipment. A manufacturer of polyacrylamide hydrogel was experiencing such challenges, so we conducted some tests to determine the best solution. We cut the specimens into rectangular strips measuring .5 inch width with about 1.5 inches of material between the grips, and ran the tests at a crosshead speed of 0.197 inches/minute (5 mm/minute). We evaluated both 100 N capacity pneumatic side-action and 100 N capacity screw action grips with a variety of serrated, smooth, and sandpaper surfaces of jaw faces to determine the optimal grip configuration.
Our results show several important findings. First, due to very low stress and strain values experienced at break, we recommend using an electromechanical test system with a 50 N load cell. We recommend using the manual screw action grips or BioPuls pneumatic grips because the ability to adjust the grip force was critical to successful testing, as specimen thickness values varied greatly. We also found that serrated faces consistently led to breaking of the material at the jaw face; not enough tightening of them led to specimen slipping. Using sandpaper adhered to a smooth face was found to be the best solution for gripping the hydrogel without slipping or premature failure.
A final recommendation for the most accurate break results is to prepare the specimens with a "dog bone-shape" die in accordance with ASTM D412. This specimen shape has a reduced gauge length area and minimizes the chance of the specimen breaking at the jaw face or tearing due to spurs on the edges of the material.
5900 Universal Testing Systems are engineered for precision, built for durability, and offer the flexibility for changing requirements. They are designed with standard and optional features that increase testing efficiency and improve the testing experience for the operator. A wide range of models are available for testing capacities from < 100N up to 600kN.
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Screw side-action grips provide a very simple and efficient method for holding test specimens in a wide range of applications. The dual - acting design of 2710-100 series grips means that jaw faces can be adjusted to accommodate different specimen thicknesses. This ensures that the line of tensile force remains concentric with the grip body. They can be equipped with a selection of interchangeable grip jaw faces in various sizes and choice of surfaces including smooth ground, rubber-coated and serrated. Line contact and special coated faces are also available.The unique ‘snap-on’ jaw face attachment makes changing faces extremely quick and simple.
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The BioPuls submersible pneumatic side action grips and temperature-controlled bath with pneumatic lifting and lowering mechanism is the ideal testing solution for a wide variety of biomedical testing applications.
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The second generation, Standard Advanced Video Extensometer, SVE 2, is a high-performance, non-contacting extensometer that is ideally suited for everyday applications such as rubber, soft plastics,elastomers and other materials with high strain to failure. It can also be used for testing in both ambient and non-ambient temperature conditions.
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