Multi-objective Topology Optimization of Thermo-mechanical Compliant Mechanisms

The material characteristics of a structure will change with temperature variation,and will induce stress within the structure.Currently,the optimal design for the topology of compliant mechanisms is mainly performed in single physical field.However,when compliant mechanisms work in high temperature environments,their displacement outputs are generated not only by mechanical load,but also by the temperature variation which may become the prominent factor.Therefore,the influence of temperature must be considered in the design.In this paper,a novel optimization method for multi-objective topology of thermo-mechanical compliant mechanisms is presented.First,the thermal field is analyzed with finite-element method,where the thermal strain is taken into account in the constitutive relation,and the equivalent nodal thermal load is derived with the principle of virtual work.Then the thermal load is converted into physical loads in elastic field,and the control equation of the thermo-mechanical compliant mechanism is obtained.Second,the mathematical model of the multi-objective topology optimization is built by incorporating both the flexibility and stiffness.Meanwhile,the coupling sensitivity function and the sensitivity analysis equations of thermal steady-state response are derived.Finally,optimality criteria algorithm is employed to obtain numerical solution of the multi-objective topology optimization.Numerical examples show that the compliant mechanisms have better performance and are more applicable if the temperature effect is taken into account in the design process.The presented modeling and analysis methods provide a new idea and an effective approach to topology optimization of compliant mechanisms in electrothermic coupling field and multiphysics fields.     

Critical Comparison of Novel and Conventional Processing for Dual-Phase Steels

The final properties of an industrial product depend on the processing route of the material. Hence there is an impetus to study different processing routes to obtain the most desirable final properties. In the present study, low carbon steels have been subjected to the novel deformation induced ferrite transformation (DIFT) technique to produce dual-phase microstructures that are composed of ultra-fine ferrite with martensite and/or bainite as a second transformation product. In this thermomechanical processing technique, the steels have been rapidly cooled from the austenitization temperature to the deformation temperature (which is at least 25°C above the Ar₃ temperature) to produce highly undercooled austenite, followed by heavy deformation, and subsequently rapidly cooled thereby facilitating transformation to fine grained ferrite. Comparing the final microstructures obtained by this route with those attained by conventional thermo-mechanical processing, it can be concluded that significant ferrite grain refinement is attainable by the novel DIFT technique thereby emphasizing its potential to achieve improved mechanical properties.     

油砂沥青改质产品中甲苯不溶物的表征

油砂沥青及其衍生产品中含有悬浮的甲苯不溶物如粘土和碳质固体颗粒，会导致后续加工过程中的结垢、催化剂失活和床层堵塞。笔者从油砂沥青衍生产品中分离出甲苯不溶物并进行了分析表征。研究发现，油砂沥青渣油中的甲苯不溶物主要是超细的硅铝酸盐粘土颗粒，结合了部分干酪根成分；焦化渣油和焦化瓦斯油储罐中沉积的甲苯不溶物类似焦炭；焦化瓦斯油中的甲苯不溶物主要是碳质有机物颗粒，但氮、氧含量相对丰富，并含少量矿物质和粘土颗粒，含氮的杂环化合物如吡咯类物质的存在可能是导致焦化瓦斯油中甲苯不溶物生成的主要因素。