Applied Mechanics and Materials Vols. 7-8

Abstract: Fatigue crack closure is an important phenomenon which needs to be taken into account in the development of models for crack propagation. This paper presents an overview of techniques for measuring crack closure. The moiré interferometry approach is described in more detail and some experimental results are presented and compared with the predictions of closure models.

Abstract: This paper provides an overview of four key challenges for structural integrity assessment methods: surface technology and incubation / initiation of defects, microstructural effects on weld performance, realistic loading and defect morphologies and thermal / irradiation effects on materials and structures. These challenges will be met by the application of emerging experimental and numerical methods which will facilitate the development of a mechanistic understanding of these four challenges alongside mechanistically-based models to enable the reliable prediction of component performance outside the available database of materials behaviour.

Abstract: A thorough investigation of the failure mechanisms of composite sandwich beams under four- and three-point bending and cantilever beams was undertaken. The beams were made of unidirectional carbon/epoxy (AS4/3501-6) facings and a PVC closed-cell foam (Divinycell) core. Two types of core material H100 and H250 with densities 100 and 250 kg/m3, respectively, were used. The failure modes investigated are face sheet compressive failure, core failure and facing wrinkling. The various modes have been studied separately and both initiation and ultimate failure have been determined. Initiation of a particular failure mode and triggering and interaction with other failure modes was also investigated.

Abstract: Cost effective and reliable operation of a power station plant and achieving low carbon dioxide emissions can be very dependent on maintenance activities. Planning maintenance to minimise the down-time of the plant is a key cost factor. It is important to have the latest data as to the age and state of the components and parts at the time of plant shut down. Indeed, deciding on the best time to shut down the plant for maintenance can depend upon trends in these data. For steam pipes, the required ageing information is the creep strain rate. These creep strain data obtained at shut down provide key information as to the needed replacement of pipes to maintain reliable plant operation. This paper presents the E.ON UK ARCMAC creep strain measurement systems that are being further developed by Imperial College London with the use of DIC and other techniques.

Abstract: This paper investigates the comparison of the measured and predicted force-displacement loops of a multiaxial representative fretting fatigue test rig for aeroengine spline couplings. A local finite element model of the fretting specimen and the fretting bridge is outlined. A more extensive model of the fretting test rig is then introduced. This global model also includes the loading structures. The model captures the compliance of the fretting test rig and improves the correlation of the observed hysteresis. This method allows the slip amplitude at the contacts to be quantified.

Abstract: The present paper proposes a new test rig to perform fretting fatigue tests on a shrinkfitted shaft assembly. A shrink-fitted shaft is put under rotating bending by means of an eccentric offset at one end. The shaft is driven near to its first resonance condition to significantly reduce the required force to produce bending. Test parameters are the imposed bending stress amplitude, and the hub radial pressure obtained through conical fitting. The proposed apparatus allows for changing bending stress amplitude and hub pressure to generate fretting fatigue tests at different conditions. In particular, the role of slip amplitude in fretting fatigue can be investigated. At the present stage the proposed apparatus is under construction at the Mechanical Department of the University of Pisa.

Abstract: The materials response of a laser beam welded joint from hot rolled DP600 steel plate to the dynamic loading has been experimentally studied by instrumented Charpy impact testing. Based on the impact force-displacement curve, Critical Crack Length, i.e. CCL and dynamic crack extension resistance curve, i.e. J-
a were determined, describing the welding joint’s crack formation toughness and the dynamic crack behavior. It is shown that the difference of crack initiation and propagation between the HAZ and BM is not significant. In addition, the CCL of Welding Area, i.e. WA is multiple higher than that of HAZ and BM, which is also less dependent of low temperature. Moreover, the J-
a curve of WA consists of two segments, the initial sudden ascending with linear feature and the subsequent slow rising. Furthermore, tearing module derived from the slope of J-
a curve was discussed, indicating the material microstructure mechanism affected by the thermodynamic process of laser beam welding.