Applied Mechanics and Materials Vols. 275-277

Abstract: Reasonably predicting the fatigue life of specimens, depends on the research and understanding of the fatigue crack propagation behavior under variable amplitude loading (VAL) rather than under constant amplitude loading (CAL). The present study aims at evaluating residual fatigue life under single overload VAL by adopting a dynamical coefficient mechanics (DCM) model which we have reported. New formulas connecting the crack length with number of cycles and expressions for the fatigue crack propagation (FCP) under single overload VAL have been derived and were used to predict crack propagation. The ratios of predicted-to-experimental lives range from 1.00 to 1.09, which indicates that the results obtained from this DCM model are in good agreement with experimental data from published literatures and cover all stages of fatigue crack growth curve.

Abstract: Abstract. In this paper, the fatigue life of the 45 # steel specimens is tested. Two groups of fatigue damage specimens are prepared for the experimental study. Their fatigue cycles respectively reached 80% and 90% of the fatigue life tested. The repairing experiments to the two groups’ specimens by the high voltage pulse discharge are finished. After these repairing experiments, the residual fatigue lives of the two group specimens repaired are tested. The results show that the residual fatigue lives of the specimens are improved greatly. The total fatigue lives of the specimens have been increased at least 160% of the fatigue life tested.

Abstract: Natural fiber reinforced composites have become excellent candidates for automotive applications and civil engineering facilities. The design procedures will require precisely evaluating the toughness of the materials, which demand accurate measurements of strain or displacement that are difficult to obtain for ductile materials. The primary objectives of this paper were to develop reliable experimental approaches which can effectively evaluate the fracture behaviors of random short natural fiber reinforced polypropylene (PP) composites. The digital image correlation method (DICM) was applied to compute the deformation fields around the crack tip of a compact-tension specimen in a process of loading. An experimental and numerical hybrid method was used to describe the fracture behaviors of the composites. The relationship between the micro-structure of random fibers and the macroscopic mechanical properties of the composites can also be understood.

Abstract: Considering transmission tower-line system coupling vibration ,construct a three dimensional finite element nonlinear analysis model for 500KV Shanghai to Xuzhou transmission line project.Execute Dynamic response analysis of transmission tower-line system under broken wire impact with SAP2000.The results show that :broken wire influence on the reaction of transmission tower-line system displacement and internal force can not be ignored ;influence on the reaction of transmission tower-line system displacement and internal force caused by ground wire broken is less while that of conductor is significant,peak value of a stem internal force can be as much as 2 times initial axial force ;the more wires are broken,the vibration response of transmission tower-line system is greater, the safety degree is lower;when it comes to internal force,there is significant difference between consider broken wire load as impact load and as static load,dynamic effects cannot be ignored.

Abstract: In order to describe hydraulically created fracture propagation’s characteristics of rock matrix exactly, in this paper, establishing a stress field ‘s calculation model of fracturing propagation tip , obtaining numerical method of fracturing propagation’s characteristics based on damaging and describing fracturing propagation’s characteristics combined with method of finite element. Research shows that the corrigendum between stress field ‘s calculation model of fracturing propagation tip and practical engineering are 0.64 percent and 1.43 percent respectively. Compared with the traditional method, the result is more exactly.

Abstract: Stress intensity factor (K) is the measure of severity of stress at the crack tip. When K exceeds the critical limit (i.e., the material fracture toughness), the crack grows. K is valid in brittle materials (LEFM) and to some extent in ductile materials also provided there is small scale yielding (SSY) at the crack tip. The paper reviews the numerical methodology to obtain KI of ductile, Mode I cracked, CT and SENB test specimens in LEFM and SSY regimes with the help of J integral method. The numerical values are successfully compared with the theoretical values.

Abstract: In the construction and excavation process of highway project in mountain area, because the value degree of the geological environment conditions and geological disasters is insufficient, so it often causes the landslide resurrection or part of the resurrection, and forms a new landslide disaster. To ensure the tunnel portal construction and the stability of the slope, this paper based on LiShigou tunnel portal slope engineering, in view of the different slope unloading plan of the LiShigou tunnel portal slope, and based on FLAC3D software to take numerical simulation analysis and comparison, then to determine the safety and the reliability of the construction,at last the optimum scheme of the unloading is choosen.

Abstract: The Main factors affecting the stability of underground caverns are selected, including the rock mechanical parameters (elastic modulus, Poisson ratio, cohesion and internal friction angle) and initial ground stress parameter (lateral pressure coefficient). Numerical test method is adopted to analyze each parameter’s sensitivity to surrounding rock displacement. Sensitivity formula making each values comparable is established. The sensitivity distribution laws are obtained, and then each parameter’s quantitative effect on displacement is discussed. This work has prominent guiding significance to engineering designs.

Abstract: Based on the method of level-layer analysis , with the sliding harmonious condition of layered backfills considered , the theoretical answers to the unit earth pressures , the resultant earth pressures and the points of application of the resultant earth pressures on retaining walls with layered non-cohesive backfills are set up . The comparisons are made with Coulomb’s formula.