【作者】 马玲；

【导师】 王勇勤；

【作者基本信息】 重庆大学 ， 机械工程， 2018， 博士

【摘要】 挤压工艺因其耗材少、生产效率高、符合现代工业绿色化的生产理念而得到广泛应用。大型挤压筒是重型挤压机的关键部件之一,其耐用性和服役寿命对挤压生产至关重要。为了探明挤压筒服役过程中性能变化规律,提高挤压筒的使用寿命,本课题建立了描述挤压筒服役过程中材料行为演化的统一粘塑性本构关系模型以及损伤累积模型;通过力学实验获取挤压筒用热作模具钢AISI H11与AISI H13的模型参数;建立挤压筒服役过程中的数值模拟模型,揭示实际挤压工况下挤压筒服役性能在蠕变-疲劳作用下的退化规律,为延长大型挤压筒的服役寿命提供理论依据和方法支撑。具体研究内容如下:(1)基于DDM法与S-N曲线以及过盈理论对挤压筒蠕变-疲劳寿命进行分析,包括多层组合式挤压筒弹性设计理论模型、弹塑性设计理论模型,以及疲劳/蠕变线性累加应力演化模型和寿命预测模型等理论研究,为研究挤压筒失效机理与服役寿命提供开创性思路。(2)热作模具钢耦合损伤演化法则的粘塑性-蠕变本构理论研究,包括分析各内变量对应参数的物理涵义及非线性关联关系,构建基于粘塑性本构框架与Lemaitre损伤法则的耦合蠕变-疲劳损伤的本构模型,以及模型参数识别与提取方法。(3)高温服役条件下热作模具钢实验研究,包括单轴拉伸试验,应变控/应力控、对称/非对称循环加载实验以及蠕变试验,以对其力学性能有全面而深刻的认识,为修正材料的本构方程以及准确预测其服役条件下的力学行为提供依据。(4)极端复杂服役环境下挤压筒性能退化规律模拟、蠕变-疲劳失效研究,包括在ABAQUS软件中开发描述材料力学响应的UMAT材料模型子程序,建立循环挤压过程中受力边界条件的加载用户子程序DLOAD与UTRACLOAD,综合分析挤压筒在服役期内应力-应变的演变规律以及损伤累积情况。(5)基于有限元模拟结果,对挤压筒的服役响应进行了相对全面的分析研究,包括挤压筒的蠕变-疲劳损伤累积、蠕变变形导致的过盈量损失、及其对挤压筒服役寿命的影响,为其设计与维护提供了重要的理论指导。更多还原

【Abstract】 Extrusion technology has been extensively used in manufacturing industry due to its merits of less material consumption,high production efficiency and environmentfriendly concept of development.Extrusion container is the key component of large presses in the extrusion industry and its durability as well as lifetime has crucial influence on the extrusion cost.In order to investigate the evolution of extrusion container’s serving properties and improve its capacity and lifetime,this study is designated to build a unified visco-plastic constitutive model coupled with damage rule to describe the response of the material AISI H11 and H13 under the condition of extrusion process.Parameters in the model are determined by a series of experiments at an elevated temperature and the numerical simulation is implemented to validate the constitutive model and the deterioration of extrusion container.This work is meaningful to prolong the lifetime of extrusion container,and it mainly includes 5 parts:(1)Lifetime analysis of creep-fatigue interaction based on the combination of DDM method,S-N curve and critical shrinkage,including the elastic/elastic-plastic design theory of compound layers and linear summation of creep/fatigue damage as well as its lifetime prediction,which offers the essential research direction to study extrusion containers’ failure mechanisms furtherly and elaborately.(2)To build the unified visco-plastic constitutive model coupled with damage rule for materials H11/H13 employed in extrusion containers,including choosing the fundamental constitutive/damage frames and making some modifications,as well as interpreting and determining the parameters in the model.(3)Design of experiments for mechanical properties investigation,including axial tensile tests,axial stress/strain-controlled symmetrical/asymmetrical cyclic tests and axial creep tests at an elevated temperature.It’s helpful to build a new or modified item in the constitutive model to indicate the specific mechanical properties of specific materials and make it more powerful and accurate.(4)ABAQUS simulation of extrusion container under cyclic extrusion loading at high temperature with the help of several user-defined subroutines UMAT,DLOAD,UTRACLOAD and UMESHMOTION,including the creep-fatigue damage accumulation,shrinkage loss between every two shrink-fitting layers and wear depth of the inner surface of the liner of the extrusion container.(5)Relatively full analysis of extrusion container’s serving responses based on finite-element simulation results,including predicting the critical position of creepfatigue crack failure and its lifetime,revealing the evolution of the shrinkage loss between every two extrusion layers along with extrusion cycles and its influence on the lifetime of the extrusion container as well as investigating the wear condition of the extrusion liner.This work is promising and useful to guide the design and maintenance of the extrusion container in order to prolong its serving lifetime.更多还原