Instron

Abstract: A hardness tester (10) is disclosed which conducts its hardness test through a penetrator impinging upon the surface of a test specimen. Enhanced accuracy and repeatibility are achieved through the use of a closed loop system and directly mounting a load cell (26) to the indentor (24), connecting a linear displacement transducer directly to the load cell and eliminating an elevating screw in initially positioning and applying load to the specimen to be tested.

Abstract: A practical method for measuring the hardness of metals at high strain rates (>10 3 s −1 ), using a dropped ball, is developed and demonstrated on cold-rolled plain carbon (1018) steel. The metal is assumed to be one-dimensional and rigid plastic. By formulating the problem in terms of the lateral, rather than the depth, dimensions of the indentation, the dynamic hardness can be obtained at load, obviating the need for rebound energy corrections. In addition, the Tabor strain equation relating to equivalent unidirectional compression is derived, and methods are also derived to include “piling-up” around indentations for plastic flow at constant volume. A previously unrecognized phenomenon that can occur in projectile indentation of metals, “ballistic strain softening”, is described. It is related to the fact that the dynamic hardness obtained by this test is a function of the ball radius times the strain rate divided by the strain. As a result, comparison of the dropped ball test flow stress data with those of constant strain rate tests requires a transform of the Tabor strain and strain rate data to constant strain rate conditions. When this is done, the dynamic yield stress data that are determined as a function of the effective strain rates agree with comparable published data for mild steel obtained using more conventional tests. The results also show that there is greatly enhanced strain hardening in irons and steels above a critical strain rate, which increases with purity. A dislocation model is used to explain this increase in terms of an additional dislocation generation mechanism coming into play.

Abstract: — The use of d.c. electrical potential methods is described for the monitoring of Mode III (anti-plane shear) fatigue cracks in circumferentially-notched cylindrical specimens subjected to cyclic torsion. Calibration of potential change with crack depth and optimization of current input and potential measurement probe locations are achieved using simple finite element procedures, and are verified experimentally. The use of the method for Mode III crack growth studies is described in the light of crack face electrical shorting problems associated with torsional crack closure.

Abstract: A grip for a material testing load frame including a grip plate for engaging the end of an elongated sample having a longitudinal axis and a grip body having one end for connecting to the grip plate and another end for connecting to a loading component of the frame, a mechanism for adjusting the concentricity of the plate with respect to the body, and a mechanism for adjusting the angle of the plate with respect to the body, so that when the sample end is engaged by the plate, and the grip body is connected to the loading component, the longitudinal axis and the axis of the loading component can be aligned with respect to the concentricity and angle.