Computational Mechanics of welds and welded structures

弧焊是一种复杂的制造工艺，其中电弧以大约1至10毫米/秒的速度在大约1平方厘米的区域内产生热量，形成体积通常略小于1平方厘米的液态金属池。当熔池后缘的液态金属在几毫秒内凝固时，就形成了焊缝。瞬态温度场驱动了材料的冶金相变和热膨胀，改变了材料的温度相关性能。在加热和冷却过程中，其显微组织相发生变化。由于结构的热胀冷缩、相变和约束引起的应变产生应力和塑性变形。塑性应变率导致残余应力、变形和损伤。在焊接过程中，会形成裂纹、气孔等各种缺陷。由于裂纹和孔隙可能是应力-应变历史的函数，因此对于设计工程师来说，对每个焊缝附近的瞬态应力和应变场进行可靠的估计以评估开裂的风险是很重要的。焊缝的残余应力对在役失效风险起着重要的作用。***本研究将训练学生开发和应用真实物理、力学和材料科学的焊接过程和焊接结构行为的真实计算机模型，用于以下计算模型；1)多道次焊缝熔合区和热影响区焊缝熔池物理及显微组织演变；2)熔池熔点至使用过程中固体的热塑性应力分析；3)焊缝的疲劳、蠕变、韧性和脆性断裂失效模式；4)焊接结构的优化设计。这些瞬态三维非线性模型被集成到一个软件框架中。该软件在工业中用于优化焊缝和焊接结构的设计，以及培训焊工，焊接工程师和检验员。***人们经常认为，焊接是电力和石化厂、船舶、桥梁和管道等结构中最不可靠的部分。设计和建造更可靠的结构的能力对加拿大来说是一个重要的利益。改进培训对加拿大焊接协会的5万多名会员来说非常重要。2009年，当AECL的NRU反应堆关闭，全球85%的同位素生产停止时，修复过程是焊接。基于NSERC资助研究的软件，用于在焊接试验开始前预测每个焊缝的设计性能，在修复的成功中发挥了重要作用。焊接协会表示，这是他们见过的最复杂的焊接修复。**

Arc welding is a complex manufacturing process in which an electric arc generates heat in an area approximately 1 cm2 while travelling at speeds of approximately 1 to 10 mm/s to form a pool of liquid metal with volume usually slightly less than 1 cm3. As the liquid metal on the trailing edge of the weld pool solidifies in milliseconds, a weld is created. The transient temperature field drives metallurgical phase changes, thermal expansion and changes temperature dependent properties of the materials. The microstructure phases change as it is heated and cooled. The strain due to thermal expansion-contraction, phase changes and restraint of the structure generates stress and plastic deformation. The plastic strain rate leads to residual stress, deformation and damage. During the welding process, various defects such cracks and pores can form. Because cracks and pores can be a function of the stress-strain history, it is important for design engineers to have reliable estimates of the transient stress and strain fields in the neighbourhood of each weld joint to assess the risk of cracking. The residual stress in welds plays an important role in the risk of in-service failure due.***This research will train students to develop and apply realistic computer models of the real physics, mechanics and material science of the welding process and the behaviour or welded structures for the following computational models; i) weld pool physics and evolution of microstructure in the fusion zone and heat-affected zone of multi-pass welds, ii) thermal–plastic stress analysis of the solid from the melting point in the weld pool to in-service behaviour, iii) fatigue, creep, ductile and brittle fracture failure modes in welds, iv) optimal design of welded structures. These transient 3D non-linear models are integrated into a software framework. The software is used in industry to optimize the design of welds and welded structures and for training welders, welding engineers and inspectors.***It is often argued that welds are the least reliable parts of structures such as power and petrochemical plants, ships, bridges and pipelines. The capability to design and build more reliable structures is an important benefit to Canada. Improved training is important for the more than 50,000 members of the Canadian Welding Association. In 2009, when AECL's NRU reactor was shut down and 85% of the worlds isotope production halted, the repair process was welding. Software, based research funded by NSERC, that was used to predict the performance of the design of each weld before welding tests began, played an important role in the success of the repair. The Welding Institute said this was the complex weld repair they had ever seen. **