Load compression test fixture (ASTM D6641)

As shown in Figure 1, the CLC fixture consists of two pairs of steel blocks, each pair of steel blocks clamped with four bolts.When installed, the ends of the 5.5-inch-long specimen are flush with the ends of the block.The steel block has a clamping surface 1.2 inches wide and is used for testing specimens with a nominal width of 1 inch.

As shown in Figure 2, these gripping surfaces are coated with tungsten carbide particles to enhance friction, allowing higher shear loads to be delivered to the specimen.And because these surfaces are relatively smooth (100 grit), they will not damage the surface of the specimen.This allows the use of unground specimens in many applications, which is a major advantage in terms of specimen fabrication costs.

By adjusting the bolt torque, the ratio of the end load and the shear load of the specimen can be controlled, that is, a combined load can be achieved.This allows the material to be successfully tested with stronger clamping forces than pure end loads (avoiding end crushing) and smaller clamping forces than pure shear loads (reducing stress concentrations caused by clamping).

The clamp blocks also prevent severe bending of the specimen.The two calibration rods in the linear bearing are used to maintain the alignment of the upper and lower pairs of clamps. The linear bearing eliminates the friction of the calibration rod.A circular groove on one side provides clearance for an edge-mounted extensometer, if used.Alternatively, bonded strain gauges can be used on one or both faces of the specimen.

The fixture with the specimen installed is placed unrestrained on the flat base of the testing machine, and is loaded directly on its top surface by a flat plate installed on the crosshead of the testing machine.