A low-cost method is presented which enables digital image correlation (DIC) with conventional cameras (i.e. not high-speed) to be used for determination of vibration deflected shapes via the use of a stroboscopic lamp and some simple ancillary circuits. For each natural frequency of the structure under consideration, a sequence of images is captured asynchronously with the vibrations using the DIC system and the resulting displacement fields are correlated with the excitation signal driving the vibration using a least-squares approach. Three approaches for performing this correlation are outlined, one of which is developed into the algorithm used for processing the present results to obtain the amplitude and phase of the vibration at each point on the specimen, allowing the deflected shape to be reconstructed. This process is illustrated using the example of a vibrating aluminium plate. The resulting shapes and frequencies agree well with finite element modal analyses of the plate.

Abstract.Crack size determination using electrical potentials both in service and in the laboratory has been undertaken for many years. In the laboratory this has mainly concentrated on the measurement of crack depth, with either alternating current (AC) or direct current (DC) supplies. Some work to determine the varying depth along the width of cracks as an inspection tool of in service parts using mapping methods has been done. This has used both AC and DC utilising various models to understand the data recorded, in Alternating Current Potential Drop (ACPD) a range of frequencies have been used to give various skin depths.The resulting analyses have been grouped into two groups 'thin skin' and 'thick skin', in the thin skin case the skin depth is significantly smaller than the depth of the crack 1/10th of the crack depth whereas in the thick skin cases are for cases where skin depth is over this limit. Some work has been carried out to try and unify these two approaches.The work presented here looks to develop a method using variable frequency ACPD to resolve further information about cracks growing in laboratory specimens. A system has been developed to rapidly sweep a wide frequency band and record voltage drop across a crack or feature. A selection of steel samples with known geometries and features have been used to trial and benchmark the technique. These samples have a range of cross sections as well as machined features or a range of shapes and sizes to simulate a range of crack geometries. This work has been approximated using a 2D computational model. This has been done using a reduced thickness approach. 165, 09004 (2018) MATEC Web of Conferences

Materials used for components such as power plant steam pipes, gas turbines discs and die forming machinery can be subject to combinations of extreme loading and temperature conditions. In addition, the materials can contain or develop cracks. Once a crack has initiated, the conditions under which the components operate can cause these cracks to propagate. This paper is concerned with the experimental testing of 316 stainless-steel, corner-cracked samples under thermo-mechanical-fatigue conditions, and the measurement of the crack propagation during testing using alternating-current-potential-difference readings. Fracture mechanics (Paris Law) methods have been used in the processing of the experimental data.

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