Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on ...Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion us-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks disappear when the value of pre-stress surpasses 0. 2 σs（yield limit）. Welded thin plates with low-level residual stress, little distortion and no hot cracks are obtained with longitudinal pre-tensile stress level between 0. 6σsand 0. 7σs and precompressive stress between 0. 2 σs and 0. 3 σs in transverse direction.展开更多
Residual stress is one of the factors affecting the machining deformation of monolithic structure parts in the aviation industry. Thus, the studies on machining deformation rules induced by residual stresses largely d...Residual stress is one of the factors affecting the machining deformation of monolithic structure parts in the aviation industry. Thus, the studies on machining deformation rules induced by residual stresses largely depend on correctly and efficiently measuring the residual stresses of workpieccs. A modified layer-removal method is proposed to measure residual stress by analysing the characteristics of a traditional, layer-removal method. The coefficients of strain release are then deduced according to the simulation results using the finite element method （FEM）. Moreover, the residual stress in a 7075T651 aluminium alloy plate is measured using the proposed method, and the results are then analyzed and compared with the data obtained by the traditional methods. The analysis indicates that the modified layer-removal method is effective and practical for measuring the residual stress distribution in pre-stretched aluminium alloy plates.展开更多
The effect of concrete creep on the pre-camber of a long-span pre-stressed concrete continuous rigid-frame bridge constructed by cantilever casting method was investigated.The difference of creep coefficients calculat...The effect of concrete creep on the pre-camber of a long-span pre-stressed concrete continuous rigid-frame bridge constructed by cantilever casting method was investigated.The difference of creep coefficients calculated with two Chinese codes was discussed.Based on the calculations,the pre-camber of a pre-stressed concrete continuous rigid-frame box bridge was computed for construction control purpose.The results show that the short-term creep coefficient and long-term creep coefficient calculated with the CC-1985 are larger than those calculated with the CC-2004,while the medium-term creep coefficient calculated with the CC-1985 is smaller than that calculated with the CC-2004.The difference of creep deformation calculated with these two codes is small,and the influences of concrete creep on the pre-camber for most of the segments are negligible.The deflections and stresses of the box girder measured during the construction stages agree very well with the predictions.展开更多
边坡工程施工过程中,采用预应力锚杆施加预紧力可约束岩土体开挖后应力重分布作用产生的过大变形,增强岩土体自身强度。针对某边坡工程中预应力锚杆穿过多层岩土体的荷载传递及锚固承载特征问题,基于连续-非连续单元法(continuum discon...边坡工程施工过程中,采用预应力锚杆施加预紧力可约束岩土体开挖后应力重分布作用产生的过大变形,增强岩土体自身强度。针对某边坡工程中预应力锚杆穿过多层岩土体的荷载传递及锚固承载特征问题,基于连续-非连续单元法(continuum discontinuum element method,CDEM)数值模拟方法,考虑复合岩土体中岩土层理结构面之间的非连续以及块体-杆件耦合计算问题,建立二维边坡复合岩土体桩锚结构数值模型,揭示复合岩土体中穿层预应力锚杆的受力特征。研究结果表明:岩土层与锚固体极限粘结强度标准值越大,产生的轴应变越小,轴力传递效应越弱,锚杆轴力衰减率越高;张拉第二、三根锚杆时,其杆体作用在张拉第一根锚杆之后岩土层自平衡后的应力场内,岩土体结构面产生的错动以及剪切蠕变导致预应力快速损失,其损失率比第一根锚杆大3%~4%;该边坡工程中锚固角度在25°左右最优,既能控制水平向受力,也能防止坡顶沉降,桩锚结构整体稳定性较好。耦合复合岩土体建模-桩锚结构承载-参数优化,深入研究复合岩土体中穿层预应力锚杆受力及其参数影响规律,研究结果将指导复合岩土体中桩锚结构设计与施工。展开更多
文摘Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion us-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks disappear when the value of pre-stress surpasses 0. 2 σs（yield limit）. Welded thin plates with low-level residual stress, little distortion and no hot cracks are obtained with longitudinal pre-tensile stress level between 0. 6σsand 0. 7σs and precompressive stress between 0. 2 σs and 0. 3 σs in transverse direction.
基金Sponsored by the National Science and Technology Major Project(Grant No.2014ZX04001011)
文摘Residual stress is one of the factors affecting the machining deformation of monolithic structure parts in the aviation industry. Thus, the studies on machining deformation rules induced by residual stresses largely depend on correctly and efficiently measuring the residual stresses of workpieccs. A modified layer-removal method is proposed to measure residual stress by analysing the characteristics of a traditional, layer-removal method. The coefficients of strain release are then deduced according to the simulation results using the finite element method （FEM）. Moreover, the residual stress in a 7075T651 aluminium alloy plate is measured using the proposed method, and the results are then analyzed and compared with the data obtained by the traditional methods. The analysis indicates that the modified layer-removal method is effective and practical for measuring the residual stress distribution in pre-stretched aluminium alloy plates.
基金Project(2008047B) supported by the Funds for Youth of Control South University of Forestry and Technology
文摘The effect of concrete creep on the pre-camber of a long-span pre-stressed concrete continuous rigid-frame bridge constructed by cantilever casting method was investigated.The difference of creep coefficients calculated with two Chinese codes was discussed.Based on the calculations,the pre-camber of a pre-stressed concrete continuous rigid-frame box bridge was computed for construction control purpose.The results show that the short-term creep coefficient and long-term creep coefficient calculated with the CC-1985 are larger than those calculated with the CC-2004,while the medium-term creep coefficient calculated with the CC-1985 is smaller than that calculated with the CC-2004.The difference of creep deformation calculated with these two codes is small,and the influences of concrete creep on the pre-camber for most of the segments are negligible.The deflections and stresses of the box girder measured during the construction stages agree very well with the predictions.
文摘边坡工程施工过程中,采用预应力锚杆施加预紧力可约束岩土体开挖后应力重分布作用产生的过大变形,增强岩土体自身强度。针对某边坡工程中预应力锚杆穿过多层岩土体的荷载传递及锚固承载特征问题,基于连续-非连续单元法(continuum discontinuum element method,CDEM)数值模拟方法,考虑复合岩土体中岩土层理结构面之间的非连续以及块体-杆件耦合计算问题,建立二维边坡复合岩土体桩锚结构数值模型,揭示复合岩土体中穿层预应力锚杆的受力特征。研究结果表明:岩土层与锚固体极限粘结强度标准值越大,产生的轴应变越小,轴力传递效应越弱,锚杆轴力衰减率越高;张拉第二、三根锚杆时,其杆体作用在张拉第一根锚杆之后岩土层自平衡后的应力场内,岩土体结构面产生的错动以及剪切蠕变导致预应力快速损失,其损失率比第一根锚杆大3%~4%;该边坡工程中锚固角度在25°左右最优,既能控制水平向受力,也能防止坡顶沉降,桩锚结构整体稳定性较好。耦合复合岩土体建模-桩锚结构承载-参数优化,深入研究复合岩土体中穿层预应力锚杆受力及其参数影响规律,研究结果将指导复合岩土体中桩锚结构设计与施工。
