The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensiona...The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution, temperature profiles and deformation behavior of the solidified shell in the mould region. Then, a three-dimensional model was adopted to calculate the shell growth, tempera- ture history and the development of stresses and strains of the shell in the following secondary cooling zones. Finally, another three-dimensional model was used to analyze the stress distributions in the straightening region, The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front, and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone, especially upon the straightening operation of the bloom casting. It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius, casting speed and secondary cooling scheme, which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.展开更多
An elasto-visco-plastic constitutive model incorporating the craze damage behavior was developed for the polypropylene(PP), by using the plastic failure model applied for the concrete, to capture the craze yielding an...An elasto-visco-plastic constitutive model incorporating the craze damage behavior was developed for the polypropylene(PP), by using the plastic failure model applied for the concrete, to capture the craze yielding and stress-whitening phenomena. In addition, the developed constitutive model was implemented into finite element codes in Abaqus to simulate the tensile deformation. The standard uniaxial tensile tests were carried out. The stress-strain curves from the uniaxial tensile tests show that the stress keeps decreasing after yielding and the yield stress rises with the increasing of the strain rate. It is worth noting that the craze damage is more visible with higher strain rate. The stress-whitening can be seen clearly around the fracture. The uniaxial tensile tests using specially designed specimen with circular holes weakening were performed for the validation of the developed model. The simulation results of the tensile deformation of the hole-weakened specimen suggest that the stress-whitening could be attributed to the equivalent visco-plastic strain. By comparing between the simulation analysis and the experimental results, the proposed model can describe the stress whitening phenomenon with good accuracy.展开更多
Rutting is a chronic disease in asphalt pavements despite several mitigation measures. Although many attempts have been made by both researchers and practitioners to develop rutting prediction models, each model, howe...Rutting is a chronic disease in asphalt pavements despite several mitigation measures. Although many attempts have been made by both researchers and practitioners to develop rutting prediction models, each model, however, has certain inherent limitations due to assumptions and data used during the development of the model. Placement of an asphalt overlay is the most common method used in Zambia to rehabilitate existing asphalt pavements. The objective of this research is to go towards developing a national rutting prediction model for use in tropical hot climates based on default finite element creep and elasto-visco-plastic analysis tools in ABAQUS. Dynamic modulus and repeated load tests are conducted on overlay mixtures designed based on the pavement residual structural adequacy from deflection tests to provide material properties for the constitutive rutting model. Unified, three dimensional linear viscoelastic boundary value problems were formulated for each five national representative pavement sections. In general, the FE （finite element） creep and elasto-visco-plastie rutting evolutions were in agreement with the measured laboratory scaled one third mobile load simulators. Performance ranking of the validated models revealed optimal pavement system combination suitable for calibration. The study recommends future directions for local adoption of the South African mechanistic-empirical design method currently being developed.展开更多
The constitutive model and equivalent deformation modulus of an arbitrary column in representative elementary volume （REV） of fractured rock mass are derived. The deformation of fractured rock mass is com- posed of ...The constitutive model and equivalent deformation modulus of an arbitrary column in representative elementary volume （REV） of fractured rock mass are derived. The deformation of fractured rock mass is com- posed of the rock part and the fracture part. The elasto-visco-plastic property is considered in this model. For the convenience in engineering practice, the complex elasto-visco-plastic model and its equivalent modulus are degraded, and tbe rock is taken as an elastic body. By statistical analysis of the geometric positions of the column and the fracture, the equivalent modulus of rock mass with arbitrary fractures is obtained.展开更多
文摘The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution, temperature profiles and deformation behavior of the solidified shell in the mould region. Then, a three-dimensional model was adopted to calculate the shell growth, tempera- ture history and the development of stresses and strains of the shell in the following secondary cooling zones. Finally, another three-dimensional model was used to analyze the stress distributions in the straightening region, The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front, and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone, especially upon the straightening operation of the bloom casting. It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius, casting speed and secondary cooling scheme, which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.
基金Project(51275185)supported by the National Natural Science Foundation of China
文摘An elasto-visco-plastic constitutive model incorporating the craze damage behavior was developed for the polypropylene(PP), by using the plastic failure model applied for the concrete, to capture the craze yielding and stress-whitening phenomena. In addition, the developed constitutive model was implemented into finite element codes in Abaqus to simulate the tensile deformation. The standard uniaxial tensile tests were carried out. The stress-strain curves from the uniaxial tensile tests show that the stress keeps decreasing after yielding and the yield stress rises with the increasing of the strain rate. It is worth noting that the craze damage is more visible with higher strain rate. The stress-whitening can be seen clearly around the fracture. The uniaxial tensile tests using specially designed specimen with circular holes weakening were performed for the validation of the developed model. The simulation results of the tensile deformation of the hole-weakened specimen suggest that the stress-whitening could be attributed to the equivalent visco-plastic strain. By comparing between the simulation analysis and the experimental results, the proposed model can describe the stress whitening phenomenon with good accuracy.
文摘Rutting is a chronic disease in asphalt pavements despite several mitigation measures. Although many attempts have been made by both researchers and practitioners to develop rutting prediction models, each model, however, has certain inherent limitations due to assumptions and data used during the development of the model. Placement of an asphalt overlay is the most common method used in Zambia to rehabilitate existing asphalt pavements. The objective of this research is to go towards developing a national rutting prediction model for use in tropical hot climates based on default finite element creep and elasto-visco-plastic analysis tools in ABAQUS. Dynamic modulus and repeated load tests are conducted on overlay mixtures designed based on the pavement residual structural adequacy from deflection tests to provide material properties for the constitutive rutting model. Unified, three dimensional linear viscoelastic boundary value problems were formulated for each five national representative pavement sections. In general, the FE （finite element） creep and elasto-visco-plastie rutting evolutions were in agreement with the measured laboratory scaled one third mobile load simulators. Performance ranking of the validated models revealed optimal pavement system combination suitable for calibration. The study recommends future directions for local adoption of the South African mechanistic-empirical design method currently being developed.
基金Foundation item： the Western Transport Construction Science and Technology Project of the Ministry of Transport of the People＇s Republic of China （No. 2009318000046）
文摘The constitutive model and equivalent deformation modulus of an arbitrary column in representative elementary volume （REV） of fractured rock mass are derived. The deformation of fractured rock mass is com- posed of the rock part and the fracture part. The elasto-visco-plastic property is considered in this model. For the convenience in engineering practice, the complex elasto-visco-plastic model and its equivalent modulus are degraded, and tbe rock is taken as an elastic body. By statistical analysis of the geometric positions of the column and the fracture, the equivalent modulus of rock mass with arbitrary fractures is obtained.
