Abstract: A method of monitoring the surface of a sample under test is provided and the method comprises the steps of: illuminating the surface with light (20) polarised in a first direction; viewing light reflected from the surface through a polarising filter (27) arranged at 90° to the first direction, wherein the surface of the sample under test is provided with a marked area where diffuse reflection of the incident polarised light will occur in order to improve the contrast between the marked area and the surface of the sample under text.

Abstract: Test apparatus comprising means for holding a sample to be tested, means for altering the strain in the sample, an optical arrangement for monitoring the sample to be tested, and processing means for processing the signals resulting from the monitoring of the sample under test, wherein the environment between the optical arrangement and the sample under test is controlled, and wherein the sample to be tested is located in a position external to the controlled environment.

Abstract: A structure testing machine for carrying out tests on a test structure (25) for an assessment of the response of the structure to test loads applied to the structure in the direction of a predetermined axis of the structure under the control of a monitored control system (21) which forms part of the machine and which has a forward path which includes an actuator (24) which is supported by a machine frame and which upon actuation applies to the test structure a test load in the direction of the predetermined axis, and a controller (22) responsive to a controller input signal and to controller parameters to apply to the actuator an actuating signal to cause the actuator to subject the test structure to a test load which produces dimensional changes in the test structure in the direction of the predetermined axis. The machine is provided with an adaptive control loop which comprises a stiffness estimator (27) which generates from the dimensional changes in the test structure adaptive control signals (E.sub.

Abstract: An extensometer includes a first element and second element to be set at a predetermined distance apart, with a coupling for setting and holding the two elements at the predetermined distance apart. The coupling is movable by the action of a biasing force to an engaging disposition in which it engages with the two elements to set and hold the two elements at the predetermined distance apart, and the coupling moves under action of the biasing force to a disengaged disposition in which it no longer holds the two elements at the predetermined distance apart upon removal or sufficient relaxation of the applied force.

Abstract: Electronic ramp function generator having a resolution of 2.sup.p = 2.sup.q .times. 2.sup.r comprising a coarse digital function generator which provides a ramp consisting of 2.sup.q equally spaced steps all of equal height, and a second and synchronized digital function generator which is connected to fill in each of the steps of the coarse ramp with 2.sup.r finer steps.