Mechanical wedge grips are ideal for high capacity tests where vice grips begin to fail. The "wedge" is a fixed piece of metal with a pair of moving grip faces. As the tensile load increases, the two grip faces slide down, creating an ever increasing gripping force which traps the sample. Wedge grips are the ideal choice for any sort of high strength metals or plastics testing.
Tighten the vise wing nut to secure the sample. Vise grips are extremely versatile and low-cost. Careful attention must be paid to the type and size of the grip face being used. The vise grip jaw options include smooth metal, rubberized, diamondized, or serrated like a metal file.
Tensile grips are used for uni-axial material testing where a sample is pulled apart from two ends. There are many variations of tensile grips for universal testing machines based on the force capacity of the procedure and the specific type of material and geometry. Many of these fixtures can use different types of inserts which can help to secure the sample. Selecting the right combination of grip and jaw inserts is critical to the success of any tensile testing application.
Many tensile tests require that the stress vector is perfectly aligned in the vertical direction. In many cases, a universal joint can be used on the top grip in order to get everything in the same plane for uni-axial testing.
Ribbons, Webbing and other types of flat strapping material are tested with a wrap grip. The width of the sample is critical, as well as the diameter of the wrapping column. This is the ideal grip for testing automotive seat belts, and tie down straps used for shipping.
Roller Grips are a great option if you are working with plastics and elastomers under 5kN-10kN. The grip actuation is quick, easy, and the roller will self tighten throughout the test. Simply move the lever up to open the grip, insert the sample, and then move the lever back down to close the grip. The mechanism is spring actuated which helps to secure the sample and continuously tighten throughout the test.
Pneumatic Grips are actuated with air pressure. The constant pressure allows the grips to maintain an even force profile and they also help to speed up the time between tests. Almost all grip types have some sort of pneumatic version. They use Foot Pedals or Hand Switches and a standard air compressor. Installing Pneumatic grips is easy.
Scissor grips are a specialized type of self-tightening fixture for tensile testing. There is a spring which exerts a constant lateral force onto the sample which tightens through the test. Scissor grips are great for testing thick pieces of wood or solid foam.
Rope grips are ideal for testing cords and other types of cylindrical or thin materials. braided cordage can also be manufactured using steel wire and synthetic fibers. The cord is wrapped around the drum a few times and then secure with the vise grip mechanism which is located at the top of the grip near the adapter connection.
Rods, screws, and other types of threaded, cylindrical samples are tested using a tensile bolt grip. The sample usually has at least one threaded end and the other end has a screw head or is also threaded. Screw call outs are used to specify the exact bolt grip.
Pressure Sensitive Adhesive (PSA) tapes are tested using a variety of peel testing procedures. Each ASTM test requires using a specific type of fixture. The two most popular are the 180 degree and 90 degree peel fixtures.
Shoulder grips are used for testing buttons, wire crimps and connectors, bottle caps, briquets, and syringes. The grips have a small ledge where the sample rests while it is pulled or pushed from the other side.
ASTM D407 - B913
Pinch grips are designed to replicate to fingers squeezing together to pull something. They are used for a variety tensile testing procedures on end consumer products such as food packaging and electronics.
Bollard Fixtures are used for testing small, cylindrical cords such as cable, individual fibers, twine, string, and wire. There are a couple of different desings of bollard grips depending on the diameter of the bollard.
Fatigue Grips are used for dynamic cyclic testing. The repetitive nature of the test causes fatigue failures to the material which are different than normal tensile failures. These grips are able to withstand both compression and tensile forces. Fatigue testing grips can also be used inside of an environmental chamber on a dual column testing machine.