查看更多>>摘要：The purpose of this study is to investigate the damage modes and residual deflection of multibeam hollow slab bridges under car explosions. To comprehensively estimate the blast response, the failure process of the bridge with different beam numbers are cautiously simulated and compared. With the experimentally validation of the constitutive laws and the fluid-structure interaction parameters, the impact analysis software Autodyn is adopted to capture the damage mechanisms and the vibration histories. After cautious numerical simulations, local punching shear failure and global flexural failure dominate the damage modes of multi-beam hollow slab bridges. Due to the oversized impact energies and the insufficient structural resistance, overall collapse is observed in bridge with 4 or 6 beams in middle and acentric explosions. For bridge with 8 or 10 beams, the formed plastic hinges imply the large residual deflection and possible overall collapse during middle explosions. Owing to the easier energy dissipation and the smaller impact areas, limited flexural damage are discovered in bridge with 8 or 10 beams under acentric explosions. Due to the limited flexural damage and the small residual deflection of the distant beams, these beams can maintain great bearing capacity and can be repaired after explosions.
查看更多>>摘要：In this paper, the study of the effect of the extrusion arc groove on the fatigue life of a wing panel with functional holes is carried out to solve the problem that the fatigue life of the wing panel is reduced due to the functional holes. The influences of the depth and angle of the extrusion arc groove on the fatigue life of the wing panel are studied by means of experiment and finite element simulation. The results show that: For the wing panel with functional holes, the fatigue life can be extended by the extrusion arc grooves, which is due to the residual stress is generated after extrusion process, that counteracts the part of the effect of the load, so that the characteristic stress is reduced. The fatigue life of the wing panel with functional holes is affected by the depth of the extrusion arc grooves. When the depth is 0-0.15 mm, the fatigue life is extended slightly; when the depth is 0.15-0.3 mm, the fatigue life is greatly extended; when the depth is more than 0.3 mm, the fatigue life is extended slowly. The fatigue life of the wing panel with functional holes is also affected by the angle of the extrusion arc grooves. The fatigue life is extended with the increase of the angle until the angle reaches the optimal angle 120 degrees. The fatigue life of the studied wing panel can be extended by more than 2.34 times with the optimal extension arc grooves.
查看更多>>摘要：The fracturing pump, the key equipment for hydrofracturing operation, is characterized by its short and uncertain service life. Firstly, the crack propagation cause on the crossbore of the fluid cylinder was analyzed macroscopically and microscopically. Then, the fatigue crack expansion rate of 17-4PH steel in corrosion was measured experimentally and applied to finite element modeling analysis. It is shown that the crack growth rate of the fluid cylinder is 6.39 times faster in corrosion than that in air. The shape and direction of the crack initiation mainly affect the stress intensity factor range of the crack front during the early crack propagation of the fracturing pump fluid cylinder. The fatigue life of the fluid cylinder is greatly affected by the cyclic alter-nating load. This manuscript helps to gain insight into the crack propagation mechanism and predict the crack propagation fatigue life of the fracturing pump after crack initiation.
查看更多>>摘要：Cr coating is widely used as a protective coating on the inner and outer surface of industrial equipment. However, current researches on Cr coatings are predominantly conducted on plane specimens, and few works have considered the effect of irregular substrates on coatings. The thermal shock behaviour and failure mechanisms of two-kind Cr coatings prepared by electro-plating and vacuum arc ion plating on non-planar structure at 900 C were investigated. The microstructure and crystalline phases of the two-kind Cr coatings were analysed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The results indicate that vacuum arc ion plating Cr coating has better thermal shock resistance. There were two typical damaged regions for both Cr coatings, i.e.the concave corner of groove and the convex corner of land. By analysing the thermal shock damage behaviour of the coatings, it is concluded that fatigue stress, thermal mismatch stress, and the inherent properties of the two-kind Cr coatings are the main reasons for the difference in the overall damage degree, and the temper-ature stress concentration in the concave corner of groove is the cause for the higher degree of thermal shock damage.
查看更多>>摘要：The application of macro synthetic fibre reinforced concrete (MSFRC) innovatively addresses the current cracking and corrosion issues associated with the prestressed concrete railway sleeper. In this paper, a structural assessment of traditional concrete sleepers reinforced with high-strength, prestressed steel and macro synthetic fibres is provided. Detailed review on the rail seat and centre sections of the railway sleeper is presented to critically evaluate the mechanical benefits and feasibility of a complete replacement of prestressed steel with macro synthetic (poly-propylene) fibres. Three types of sleeper were individually subjected to both positive and negative moments at these critical sleeper sections for their performances to be compared at cracking, ultimate capacity and failure. Accordingly, the potential implementation of MSFRC in sleepers has been proposed to cost-efficiently improve the current design for the railway industry.
查看更多>>摘要：The cutterhead of the tunnel boring machine (TBM) is a large-scale metal welded structure, which is prone to some problems such as wear and cracking during the tunnelling process. Considering this phenomenon, a damage tolerance based fatigue crack propagation rate model for the cut-terhead with different reliability is established in this paper. Based on the fatigue load spectrum, the fatigue propagation life of the cutterhead with different reliability is calculated, the main factors affecting the reliability of the cutterhead are analyzed, and the engineering experiment is carried out. The results of finite element analysis show that three dangerous failure positions of the cutterhead are the junction of the split plane, the maximum deformation of the block and the center cutter seat. The load stress amplitude and initial crack size are the main factors affecting the crack propagation life and the reliability of the cutterhead. As the load stress amplitude and the initial crack size of the cutterhead increase, the fatigue crack propagation life and the reli-ability of the cutterhead decrease. Moreover, when the initial crack size of the cutterhead is greater than 0.5 mm, the fatigue crack propagation life of the cutterhead decreases dramatically. The research results provide a scientific basis for the crack detection, the life prediction and the reliability evaluation of the cutterhead.
查看更多>>摘要：The objective of this research is to investigate the H-induced fracture behavior of Fe-6Mn-0.2C-3Al-0/0.6Si steels. Two hot-rolled steels are inter-critical annealed (0Si and 0.6Si), containing gamma + alpha-ferrite. Additionally, 0.6Si contains abundant 8-ferrite, exhibiting thin plate morphology. As for 0Si, H-induced cracks (HICs) nucleate at gamma(alpha')/alpha interfaces. Then HIC's propagation is not only transgranular cracking but also intergranular cracking. However, H-induced fracture behaviors of 0.6Si on various planes are different. As for RD//TD surface, HICs preferentially nucleate at boundaries and interior of delta-ferrite, thus reveal the intergranular cracking and the transgranular cracking, contributing to the rugged river pattern strips on fractograph. As for RD//ND surface, the layered coarse-grained delta-ferrite and layered fine-grained gamma + alpha-ferrite are stacked in sequence, which is like a composite material. The existence of the shear stress and dislocation pile-up at interfaces of (gamma(alpha') + alpha)/8 and gamma(alpha')/alpha results in HIC's preferential nucleation. Then, HICs preferentially pass through the structure of gamma(alpha') + alpha-ferrite.
查看更多>>摘要：This work proposes an efficient FE-based approach for reproducing dynamic crack propagation phenomena in quasi-brittle materials. The proposed model uses a Moving Mesh technique based on the Arbitrary Lagrangian-Eulerian formulation (ALE) to adapt the computational mesh consistently to the geometry variations caused by dynamically growing cracks. Specifically, the motion of mesh nodes occurs according to Fracture Mechanics criteria, which provide suitable conditions regarding the direction and velocity of a growing crack tip. These conditions usually depend on the Dynamic Stress Intensity Factors (DSIFs) at the crack front. For extracting the DIFSs at a moving crack tip, this work introduces the ALE formulation of the dynamic M-integral as a key novelty. This strategy offers the key advantage of performing numerical integration procedures on deforming finite elements without losing accuracy. The validity of the proposed method has been assessed through comparisons with experimental and numerical data reported in the literature.
查看更多>>摘要：A detection method integrating modal deflection and natural frequency is proposed to locate and quantify the damage of the beam. A damage identification index using modal deflection curvature difference is developed to locate damage. Note that the modal deflection is derived from the flexibility matrix and virtual force. A damage quantification equation is established by the transfer matrix method, which includes the parameters of natural frequencies, damage co-efficients and damage location. Since the damage location parameters are determined by the proposed damage identification index, the damage coefficients of the damaged segments can be determined from the natural frequencies according to the damage quantification equation. The proposed damage detection method is verified numerically and experimentally. The results indicate that the proposed method can well locate and quantify the local damage of beams, especially for the beams with non-uniform damage degradation. The proposed damage locali-zation index is more appropriate to locate damage than the index using modal flexibility cur-vature (MFC) or modal flexibility curvature matrix (MFCM).
查看更多>>摘要：Flash-butt welding (FBW) has recently been employed to construct continuously welded rails. However, the failure mechanisms of FBW joints remain unclear. In this study, the weldability of mobile flash-butt welded joints was investigated in terms of microstructures, mechanical properties, and residual stresses. The microhardness test results indicated that the heat-affected zone (HAZ) of the PG4 welds showed significant reductions in hardness of up to 140 HV, whereas the digital image correlation (DIC) measurements showed high heterogeneous strains of up to 4%. Crystallographic analysis indicated that the grains in the HAZ underwent plastic strain with a lattice reorientation of approximately 80% and 55% in the face-and body-centred cubic phase, respectively. The uniaxial tensile tests established the phenomenological relationship between the bond strength and HAZ width: specifically, the bond strength was relatively high at the foot and head of the rail, progressively decreased at the web, and was inversely correlated with the HAZ width. A fractographic analysis confirmed that the shrinkage cracks, inclusions, and flat spots in the rail web were the main cause of early failure in uniaxial tensile tests. Residual stress measurements also showed that FBW can introduce high residual stresses in the rail web of up to 436.76 +/- 18.10 MPa and 225.80 +/- 12.94 MPa in the vertical and longitudinal directions, respectively. The results of this study reveal that the bond strength of mobile FBW can be assessed based on their HAZ width and provide reliable guidelines for improving the safety and stability of railway systems.
NSTL
Elsevier