Key Engineering Materials Vols. 452-453

Abstract: Stress distribution at the contact edge is known to have a dominant influence on fretting fatigue strength. Stresses acting on the contact surface are tangential stress and compressive stress. In the present study, fretting fatigue strengths of 12 Cr steel specimen under two different mean stresses have been predicted based on the generalized tangential stress range - compressive stress range diagram. The generalized tangential stress range - compressive stress range diagram was obtained by carrying out fretting fatigue tests and finite element analysis using various steel specimens with various geometries of contact pad from the previous studies. The predicted fretting fatigue strengths were in good agreement with the experimental results.

Abstract: Stress corrosion cracking (SCC) is a brittle fracture of a ductile material under severe environment. Due to the complexity of mechano-chemical degradation during SCC formation, the scientific community is still far from the complete understanding of this phenomenon. Moreover, it is commonly misunderstood that polymeric materials is ‘SCC-free’, but it should be noticed that SCC is universal phenomenon for all engineering materials including polymers. In this paper, the similarity and differences of SCC in different materials, such as carbon steels and engineering polymers, are observed and reported. The SCC modeling in carbon steels and engineering polymers is also compared and discussed.

Abstract: This paper is focused on developing fatigue-load model for highway bridges based on the measurements data of WIM (Weigh-in-Motion) in China. In this paper, based on the analysis of vehicle flow data collected from six toll stations on Jing-Fu Highway which is one of the busiest highways in China, spring festival index and month index of vehicle flow are obtained. The finite element models are established, and the vehicle flows are modelled by using Monte Carlo method as dynamic load applied on the nodes of the models. This paper presents a fatigue truck model for Jing-Fu Highway bridges, which may also be used for other highway bridges in China. In order to validate the model, strain time histories were obtained through field strain measurements for 3 existing bridges on this highway. In addition, comparison among the model introduced in this paper and the models in foreign codes as well as the models developed by other researchers is presented.

Abstract: Electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy was used to assess the fatigue damage induced in stainless steels. The parameter of the crystal grain size was devised in order to evaluate the fatigue damage in terms of the crystal grain size. It was concluded that the fatigue damage could be evaluated by the EBSD measurements using the relationship between the total strain range, the number of cycles and the crystal grain size.

Abstract: In this study, the preliminary finite element analysis of shot peening was carried out in order to investigate the fundamental mechanism of shot peening for stainless steels. For numerical simulations with high-rate deformation such as shot peening, rate-dependence plasticity models are necessary to get better analysis results. Therefore the stress-strain relation at high-strain rates of austenitic stainless steels were obtained by split Hopkinson pressure bar (SHPB) tests. The parameters of Johnson-Cook plasticity model were determined from the result, and then the finite element analysis of shot peening was carried out using the parameters. Consequently, the compressive residual stress was created beneath the surface of the target but was changed to the tensile residual stress with an increase in the depth.

Abstract: Experiments and numerical simulations were conducted to investigate the propagation patterns of pre-existing 3-D elliptical crack in rock-like material under uniaxial tension. Research results demonstrated that as the load was increased, the wrapping wing cracks initiated near the front of long axis of crack, with the lateral growth of initial crack close to the front of short axis. A distortion surface formed from the growth of initial crack leaded to the macro fracture of samples. The distribution laws of mixed-mode stress intensity factor (SIF) along crack contour were derived with FRANC3D, and propagation process of 3-D crack under tension was simulated. It was concluded that propagation patterns of 3-D crack under tension were quite different from compressive cases, mainly in aspects of growth orientation and velocity.

Abstract: The extrusion of a space frame must be followed by forming operations of some kind to obtain the desired shape/curvature, for example a stretch bending process. Therefore, one has to face with problems as production tolerances and cross-sectional distortions of the curved product. In house experience combined with trial–and–error procedures have been traditionally used to cope with the said problems. Aircraft frames show significant residual stresses as a consequence of plastic forming processes. A great number of variables, such as initial frame length and/or final additional stretch, can influence the stress state of frames determining their life and efficiency under operating loading conditions. In the present paper, we refer about the experimental evaluations of the residual stress state of aircraft frames which have carried out taking into account different process parameters. The experimental results obtained and discussed show some interesting trends: they demonstrate that the residual stresses of the formed component can be controlled and reduced.

Abstract: An experimental and numerical study of the cyclic deformation and low-cycle fatigue behaviour of the aluminium alloy AlCu5BiPb–T8 is presented. The experimental program included monotonic tensile tests, symmetric and unsymmetric strain-controlled fatigue tests, fracture toughness tests, as well as fatigue crack initiation and propagation tests. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is proposed. This algorithm is implemented into the finite element program ABAQUS and applied to the analysis of a crack growth near the notch. The accuracy of the computational procedure is tested by comparing the computed results with the real experimental data.

Abstract: An enhanced nucleation heat treatment process was employed to refine the grain structure of 7075Al/ 7wt.% SiCp metal matrix composite material. The grain structure of the metal matrix composite was investigated. The resulting microstructures were compared. It was found that a fine grained microstructure developed after the rapid heat treatment process. An increase in hardness was achieved, with hardness increasing from 129 HV in the cold extruded state to 137 – 153 HV after the heat treatment process.

Abstract: Active acoustic monitoring can capture two types of fracture behavior in rock samples, opening and closure of an existing fracture and tip movement of a propagating fracture. The first type is related to wave transmission across the fracture interface. The second one is related to the travel times of waves that diffract at the fracture tip. A series of experiment has been conducted with an acoustic system that has transducers mounted on the loading frames of a tri-axial cell situated in the Rock Mechanics Laboratory, TUDelft, the Netherlands. The existing fractures are formed by cleaving the rock samples into layers and putting them back together. The propagating fractures were created by hydraulic fracturing via bore-hole injection. The tests in this study featured both cleaved and hydraulic fractures, and aimed to characterize the interaction between them. This paper focus on the data processing that is adapted to these special tests and comparison between the monitored and recovered fractures.