Effect of welding sequence on residual stress and distortion in flat-bar stiffened plates

Numerical simulation based on finite element modelling is used to study the influence of welding sequences on the distribution of residual stress and distortion generated when welding a flat-bar stiffener to a steel plate. The simulation consists of sequentially coupled thermal and structural analyses using an element birth and death technique to model the addition of weld metal to the workpiece. The temperature field during welding and the welding-induced residual stress and distortion fields are predicted and results are compared with experimental measurements and analytical predictions. The effect of four welding sequences on the magnitude of residual stress and distortion in both the plate and the stiffener is investigated and their effects on the ultimate strength of the stiffened plate under uniaxial compression are discussed. Appropriate conclusions and recommendations regarding the welding sequence are presented.     

美国高铁困局

<正>2009年4月16日上午,奥巴马总统在副总统和交通部长的陪同下,宣布将从经济复苏计划(又称"经济刺激计划")中拨出80亿美元,用于兴建横贯美国的高速铁路干线,此外,未来连续5年里,每年都会另投资10亿美元用于高铁项目。"想象一下吧,以超过100英里的时速呼啸穿过大大小小的城镇,起点站离家门口不过几步路,终点站距目的地不过几个街区之遥。"奥巴马说道,"这是一项多