A mechanical model of a fracturing viscoelastic material was developed to investigate viscous effects in a dynamically growing crack-tip field. It was shown that in the stable creep-growing phase,elastic deformation a...A mechanical model of a fracturing viscoelastic material was developed to investigate viscous effects in a dynamically growing crack-tip field. It was shown that in the stable creep-growing phase,elastic deformation and viscous deformation are equally dominant in the near-tip field,and stress and strain have the same singularity,namely,(σ,ε ) ∝ r?1 /( n?1) . The asymptotic solution of separating variables of stress,stain and displacement in the crack-tip field was obtained by asymptotic analysis,and the resulting numerical value of stress and strain in the crack-tip field was obtained by the shooting method and the boundary condition of a mode I crack. Through numerical calculation,it was shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M . When n →∞,the asymptotic solution of a viscoelastic material can be degenerated into that of Freund's elastic-ideally plastic material by analyzing basic equations.展开更多
Some possible alternative solutions of near-tip fields are studied for plane-strain Mode-I qua- si-static steady crack growth in incompressible(v=1/2)elastic perfectly-plastic media.A group of four-sector so- lutions ...Some possible alternative solutions of near-tip fields are studied for plane-strain Mode-I qua- si-static steady crack growth in incompressible(v=1/2)elastic perfectly-plastic media.A group of four-sector so- lutions and a three-sector solution in which the elastic-unloading region vanishes are given.Stress functions,plas- tic flow factors and plastic strains in each region are also given.展开更多
Based on the theoretical framework for crack growth analysis provided by Gao and Hwang, the 5-sector soiution of near-tip fields of mode-I cracks growing quasi-statically and steadily in compressible elastic perfectly...Based on the theoretical framework for crack growth analysis provided by Gao and Hwang, the 5-sector soiution of near-tip fields of mode-I cracks growing quasi-statically and steadily in compressible elastic perfectly plastic materials is obtained.As Poisson's ratio v tends to 1/2,the 5-sector solution degener- ates to the 4-sector solution of near-tip fields of crack growth in incompressible elastic perfectly plastic materials.展开更多
A higher order asymptotic solution of near-tip field is studied for plane-atrain Mode-Ⅰ quasi-static steady crack growth in the incompressible (v=1/2) elastic perfectly-plastic media.The results show that the near-ti...A higher order asymptotic solution of near-tip field is studied for plane-atrain Mode-Ⅰ quasi-static steady crack growth in the incompressible (v=1/2) elastic perfectly-plastic media.The results show that the near-tip stress and strain are fully continuous,and the strain possesses In (A/r) singularity at the crack tip.The expressions of the stress,strain and velocity in each region are also given.展开更多
The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investiga...The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investigated. The initiating, growing, cracking and breaking of hydrogen blis-ters are as follows. Supersaturated vacancies can increase greatly during charging and gather together into a vacancy cluster (small cavity). Hydrogen atoms become hydrogen molecules in the vacancy cluster and hydrogen molecules can stabilize the vacancy cluster. The small cavity becomes the nucleus of hydrogen blister. The blister will grow with enter-ing of vacancies and hydrogen atoms. With increasing hy-drogen pressure, plastic deformation occurs first, the hydro-gen blister near the surface extrudes, and then cracks initiate along the wall of the blister with further increasing hydrogen pressure. A cracked blister can grow further through propa-gating of cracks until it breaks.展开更多
In the 5-sector solution by Drugan et al. for near-tip field of plane strain crack growing in compressible materials, the plastic flow rule is violated in the plastic zone (called the nonsingular zone by Rice) between...In the 5-sector solution by Drugan et al. for near-tip field of plane strain crack growing in compressible materials, the plastic flow rule is violated in the plastic zone (called the nonsingular zone by Rice) between the central fan sector and the elastic unloading sector. Based on the theoretical framework provided by Rice and supplemented by the "unloading boundary theorem", the correct formulation of the problem is given and the correct asymptotic solution for the near-tip field of the crack growth is obtained.展开更多
基金Supported by the Nature foundation of Heilongjiang Province under Grant No. A009 the foundation of Harbin Engineering University under Grant No. HEUF04005.
文摘A mechanical model of a fracturing viscoelastic material was developed to investigate viscous effects in a dynamically growing crack-tip field. It was shown that in the stable creep-growing phase,elastic deformation and viscous deformation are equally dominant in the near-tip field,and stress and strain have the same singularity,namely,(σ,ε ) ∝ r?1 /( n?1) . The asymptotic solution of separating variables of stress,stain and displacement in the crack-tip field was obtained by asymptotic analysis,and the resulting numerical value of stress and strain in the crack-tip field was obtained by the shooting method and the boundary condition of a mode I crack. Through numerical calculation,it was shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M . When n →∞,the asymptotic solution of a viscoelastic material can be degenerated into that of Freund's elastic-ideally plastic material by analyzing basic equations.
基金Project supported by the State Education Commission under a funding program for Excellent University Young Faculties and National Natural Science Foundation of China.
文摘Some possible alternative solutions of near-tip fields are studied for plane-strain Mode-I qua- si-static steady crack growth in incompressible(v=1/2)elastic perfectly-plastic media.A group of four-sector so- lutions and a three-sector solution in which the elastic-unloading region vanishes are given.Stress functions,plas- tic flow factors and plastic strains in each region are also given.
基金The project supported by the National Natural Science Foundation of China.
文摘Based on the theoretical framework for crack growth analysis provided by Gao and Hwang, the 5-sector soiution of near-tip fields of mode-I cracks growing quasi-statically and steadily in compressible elastic perfectly plastic materials is obtained.As Poisson's ratio v tends to 1/2,the 5-sector solution degener- ates to the 4-sector solution of near-tip fields of crack growth in incompressible elastic perfectly plastic materials.
基金The project supported by National Natural Science Foundation of China
文摘A higher order asymptotic solution of near-tip field is studied for plane-atrain Mode-Ⅰ quasi-static steady crack growth in the incompressible (v=1/2) elastic perfectly-plastic media.The results show that the near-tip stress and strain are fully continuous,and the strain possesses In (A/r) singularity at the crack tip.The expressions of the stress,strain and velocity in each region are also given.
基金This work was supported by the National Natural Science Foundation of China(Grant No.50471096).
文摘The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investigated. The initiating, growing, cracking and breaking of hydrogen blis-ters are as follows. Supersaturated vacancies can increase greatly during charging and gather together into a vacancy cluster (small cavity). Hydrogen atoms become hydrogen molecules in the vacancy cluster and hydrogen molecules can stabilize the vacancy cluster. The small cavity becomes the nucleus of hydrogen blister. The blister will grow with enter-ing of vacancies and hydrogen atoms. With increasing hy-drogen pressure, plastic deformation occurs first, the hydro-gen blister near the surface extrudes, and then cracks initiate along the wall of the blister with further increasing hydrogen pressure. A cracked blister can grow further through propa-gating of cracks until it breaks.
基金Project supported by the National Natural Science Foundation of China
文摘In the 5-sector solution by Drugan et al. for near-tip field of plane strain crack growing in compressible materials, the plastic flow rule is violated in the plastic zone (called the nonsingular zone by Rice) between the central fan sector and the elastic unloading sector. Based on the theoretical framework provided by Rice and supplemented by the "unloading boundary theorem", the correct formulation of the problem is given and the correct asymptotic solution for the near-tip field of the crack growth is obtained.
