Key Engineering Materials Vols. 385-387

Abstract: In the recent years the road accident analysis has been one of the main fields of research for automotive engineering, because of the heavy costs which Europe has to sustain each year in terms of injuries, fatalities and related costs. In this paper, starting from an impulsive model available in literature, a numerical characterization of vehicle collisions and deformation process is proposed and validated, identifying the main parameters which describe the vehicle impact behaviour. The study, conducted by using both empirical and numerical data (simulated trough Ls- Dyna), analyses the impact process by considering several situations, with different severity and geometry of impact; furthermore, with reference to the main parameters which describe the vehicle behaviour in the impact, the authors present a wide analysis, classified according to the severity of impact and to the different parts of the vehicle structure which absorb the impact energy.

Abstract: Based on Green’s function, complex function and multi-polar coordinate system, the far field solution of SH wave scattered by an elastic half space with a circular cavity and a crack at an arbitrary position and orientation is investigated. First, a suitable Green’s function is constructed, which is the fundamental solution of the displacement field for a half space with a circular cavity subjected to an out-plane time-harmonic line force at an arbitrary position in half space. Second, by means of crack-division technique, a crack with any location and orientation can be constructed in the region of the half space. The displacement field and stress field are established in the situation of coexistence of circular cavity and crack. At last expressions of far field, such as displacement mode of scattering wave are deduced. Some examples and numerical results are illustrated. The influences of the combination of different media parameters on solutions of far field are discussed.

Abstract: Rotating bending fatigue tests were carried out to investigate the effects of temperature on the fatigue strength and the fracture mechanism of an 18 % Ni maraging steel at room and elevated temperatures of 473K and 673K. Fatigue strength was higher at elevated temperatures than at room temperature, though static strength was decreased by softening at elevated temperature. There was no effect of temperature on crack morphology and fracture mechanism. On the other hand, during fatigue process at elevated temperature, the specimen was age-hardened and the specimen surface was oxide. That is, the increase in fatigue strength at elevated temperature was mainly caused by the increase in hardness due to age-hardening and suppression of a crack initiation due to surface oxidation.

Abstract: The cumulative damage of the reinforced concrete (RC) crane girders occurred by overload, fatigue and other reasons in service may deteriorate the safety of RC crane girders seriously, so it is necessary to analyze the damage mechanism and rationally reinforce them in good time. In this paper, RC crane girder strengthened with CFRP strips is taken as a target, and the mechanical performance degradation under fatigue load is studied. According to the basic theory of continuum damage mechanics, a damage variable is defined by flexural rigidity, and fatigue- cumulative damage model, which describes the process of damage and fracture, is established. The variation law of cumulative damage of RC crane girders strengthened with FRP strips under crane load is discussed, and the failure patterns such as concrete cracking, debonding between CFRP strips and concrete, yield of steel bars etc., are studied. The criterion which can be used to estimate the cumulative damage degree of strengthened RC crane girders is proposed. Finally, the evolution of the fatigue damage in the RC crane girders strengthened with CFRP strips is numerically simulated, and the results show that the proposed model can correctly describe the damage and failure process of strengthened RC crane girders. The research will provide a reference for the damage analysis and reinforcement of RC crane girders strengthened with CFRP strips.

Abstract: Usually, development of automobile brake hose and power steering hose has been realized through evaluating several actual prototype hoses experimentally. Recently, high durability and high development effect for brake hose has been required because periodic exchange for the brake hose has not been requested any more. In this study, therefore, stress analysis by FEM is performed to the crimped portion of hydraulic pressure brake hose in order to promote the development of the automobile hoses more efficiently. It is found that large normal stresses σr in the radial direction appear at the crimped portion between the nipple and inner rubber. The results suggest that several grooves on the nipple surface may be useful because they cause large σr, which may improve the sealing performance. The effect of permanent deformation of the rubber on the sealing performance is discussed by assuming initial deformation of the rubber at the crimped portion.

Abstract: In this paper, FFS assessment procedure for the buckle damaged pipeline with cracks in the girth welds is presented. For FFS assessment the tensile and J R-curve data from a pre-strained pipeline material, API 5L X65 were obtained in the laboratory to study the influences of the large plastic strain on the material properties and the fracture resistance of the pipeline girth welds. Tensile and single edge notch bend specimens in as-received, 10% pre-strained and 20% prestrained conditions were tested. The test results show significant increase in yield and tensile strength in the pre-strained specimens. Generally, the elongation and fracture resistance decreased after pre-straining. In FFS material specific failure assessment diagrams (FADs) generated based on the stress-strain curves obtained from testing were used. The critical flaw sizes of the pipeline girth welds were calculated, and the influence of the large plastic strain on the FFS results was discussed.

Abstract: Fracture behavior and the microstructure of Ti3AlC2 ceramics prepared by SHS/PHIP method were studied. Stress-strain curves at different temperature with a strain rate of 1×10-3 s-1 were obtained. Fracture toughness, flexural strength, crack propagation behavior and compressive deformation of specimens were investigated. Results show that the microstructure of the large size Ti3AlC2 ceramics prepared by SHS/PHIP method has typical layered feature of ternary carbide compound. The bridge-link phenomena induced by the flaky grains occurred in three-point bending test. It restrained the crack propagation and improved the fracture toughness of the material. Cylindrical specimens under axial compression usually smashed into chips for most of the ceramics materials, however, for the Ti3AlC2 ceramics prepared by SHS/PHIP, shear fracture along 45º incline of the specimen occurred at room temperature, and bulging deformation without any crack exhibited when temperature was high. It is concluded that the Ti3AlC2 ceramics prepared by SHS/PHIP has better fracture-resistance properties.

Abstract: The ingress of chloride ions plays a crucial role for service life design of reinforced concrete structures. In view of durability design of concrete structures under marine environment, one of the most essential parameters is the surface chloride content of concrete. With the social and technical backgrounds, the research approach of this study starts with the calculation of the amount of chloride ingredients in normal sea water. The capillary pore structure is modeled by numerical simulation model HYMOSTRUC and it is assumed to be completely saturated by the salt ingredients of seawater. In order to validate this approach, the total chloride content of the mortar and concrete slim disc specimen was measured after the immersion into the artificial sea water solution. Additionally, the theoretical, the experimental and in-situ investigation results of other researchers are compiled and analyzed. Based on this approach, it will follow to calculate the maximum surface chloride content of concrete in the tidal zone, where the environment can be considered as subjected to dry-wetting cycles.

Abstract: High cycle fatigue properties and failure mode in high strength steel tempered at low temperature were studied. The material used was Ni-Cr-Mo steel, JIS SNCM439, which was tempered at 453 K. After heat treatment, round bar specimens with hourglass shape were machined. Fatigue tests were performed using two kinds of specimens with two surface conditions, i.e., as-ground specimen and buff-finished specimen. Tests were conducted under rotating bending and axial loading. Under rotating bending, in as-ground specimens, fatigue failure took place in high cycle region above 107 cycles and failure mode was surface-related. On the other hand, buff-finished specimens exhibited the step-wise S-N curve, i.e., the subsurface fracture with a fish-eye was observed. However, under axial loading, even in buff-finished specimens the subsurface fracture didn’t occur due to small nonmetallic inclusions. Based on the results, the fatigue limit was estimated by the statistics of extremes. The prediction gave the conservative values.

Abstract: An expert system (ES) prototype in structural component design based on fracture mechanics analysis was developed recently. The system consists of several main functional parts. Among them, the inference engine is the control structure of ES which allows the expert to use searching strategies to test different hypotheses and arrive at ES conclusions. A general inference engine which can perform different inference by loading up different knowledge bases and a set of track explanation mechanism which ensure the inference process visible and reliable were established and discussed in this paper.