STATISTICAL MECHANICS MODEL OF LIQUID BINARY ALLOY AND ITS PARAMETERS

ＳＴＡＴＩＳＴＩＣＡＬＭＥＣＨＡＮＩＣＳＭＯＤＥＬＯＦＬＩＱＵＩＤＢＩＮＡＲＹＡＬＬＯＹＡＮＤＩＴＳＰＡＲＡＭＥＴＥＲＳ①ＦａｎＣｈｅｎｇｃａｉ，ＷａｎｇＪｉａｎ，ＬｉＷｅｎｃｈａｏ，ＱｉａｎＪｉａｘｕＵｎｉｖｅｒｓｉｔｙｏｆＳｃｉｅｎｃｅａｎｄＴｅ...     

A new fracture mechanics model for multiple matrix cracks of SiC fiber reinforced brittle-matrix composites

A new model is proposed for multiple matrix cracking in order to take into account the role of matrix-rich regions in the cross section in initiating crack growth. The model is used to predict the matrix cracking stress and the total number of matrix cracks. The model converts the matrix-rich regions into equivalent penny shape crack sizes and predicts the matrix cracking stress with a fracture mechanics crack-bridging model. The estimated distribution of matrix cracking stresses is used as statistical input to predict the number of matrix cracks. The results show good agreement with the experimental results by replica observations. Therefore, it is found that the matrix cracking behavior mainly depends on the distribution of matrix-rich regions in the composite.     

Fundamental studies of driven and self-propelled rotary tool cutting processes—II. Experimental investigation

An extensive experimental investigation has been carried out to verify the developed mechanics of cutting analyses for the fundamental driven and self-propelled rotary tool cutting processes. This involved testing the dynamic or perfect equivalence between the rotary tool and equivalent classical processes over a wide range of inclination angles, cut thickness and rake angles using statistical processing techniques. The collinearity conditions at the shear plane and rake face have also been tested as part of the model verification. It has been shown that all the force components, deformation and basic cutting parameter trends and quantities required for perfect equivalence have been satisfied as were the necessary collinearity conditions. The verified models provide a deeper understanding of the cutting mechanics and characteristics of these ingenious material removal operations and form the basis for the development of predictive cutting models for the fundamental and complex practical rotary tool operations.     

Prediction of the strength distribution for unidirectional fibre reinforced composites

A statistical model is proposed which predicts the strength distribution of composites. It accounts for the following parameters: fibre strength distribution, fibre spatial distribution, fibre-matrix interface properties, matrix plasticity, load transfer at broken fibres and load profile of the specimen (bending or tension). The model is solved via Monte Carlo simulation for small specimens and via an analytical approach for large parts. Both techniques predict well the strength distribution of the composite. Aluminium matrix composites reinforced with unidirectional ceramic fibres show a large scatter in three point bending strength. This scatter is caused by the probability that a cluster of broken fibres of a critical size occurs at a given stress level. When the limiting stress is reached the critical cluster grows in an unstable way leading to catastrophic failure of the specimen. The results obtained by this model agree favourably with the experimental findings and indicate that strength prediction using other concepts, like fracture mechanics, global load sharing, a simple rule of mixtures or Weibull statistics, is unreliable for predicting the strength of large composites.     

液流管路损失计算专家系统

液压传动系统中,由于密封泄漏、管道突变等原因,造成能量损失.管路能量损失计算涉及了流体力学理论模型、复杂的公式计算以及实际应用问题.本文论述了在基于AutoCAD环境下开发的液流管路损失计算专家系统,提出了新的流体力学设计思想和方法,实现了流体力学设计的信息化.     

钛合金材料砂带磨削表面残余应力形成模型及其实验研究

目的建立钛合金材料砂带磨削参数到磨削后表面残余应力之间的数学模型并验证其有效性。方法综合应用弹性力学和碰撞力学建立材料表面微观结构力学模型,通过对外力作用下的力学模型的分析计算得到数学模型,再利用Simulink对其进行仿真分析,得到了一定磨削参数下钛合金砂带磨削表面残余应力与时间的关系图,最后进行了钛合金砂带磨削实验,验证了该数学模型的有效性并进行误差分析。结果所构建的数学模型仿真值与实测值变化趋势相似,有着较好的仿真效果。但是,在引入热量系数?之前,最大误差为62.98%,平均误差为16.43%,结果不够理想;而在引入热量系数?之后,最大误差为9.87%,平均误差为5.75%,精度上升明显,能够有效地预测表面残余应力的取值。结论综合应用弹性力学和碰撞力学来构建出钛合金材料砂带磨削表面残余应力形成模型,能够有效地表征其在一定加工参数下的表面残余应力。     

Prediction of cutting forces in three and five-axis ball-end milling with tool indentation effect

Simulation of multi-axis ball-end milling of dies, molds and aerospace parts with free-form surfaces is highly desirable in order to optimize the machining processes in virtual environment ahead of costly trials. This paper presents a mechanics model that predicts the cutting forces in feed (x), normal (y) and axial (z) directions by modeling the chip thickness distribution, and cutting and indentation mechanics. The shearing forces are based on commonly known cutting mechanics models. The indentation of the cutting edge into the work material is modeled analytically by considering elasto-plastic deformation of the work material pressed by a rigid cutting tool edge with a positive or negative rake angle. The distribution of chip thickness and geometry of indentation zone are evaluated by considering five-axis motion of the tool along the toolpath. The proposed model has been experimentally validated in plunge indentation, as well as in three and five-axis ball-end milling of free-form surfaces. The prediction of axial (z) cutting forces is shown to be improved significantly when the proposed indentation model is integrated into the mechanics of ball-end milling.     

A first-principles thermodynamic approach to ordering in Ni-Mo alloys

There is a competition between several face centered cubic (FCC)-based ordered inter-metallic phases in Ni-Mo alloys containing 8-33 at% Mo. The transformation behavior of these alloys in terms of ordering instabilities has been studied. First-principles tight-binding-linear muffin-tin orbital (TB-LMTO) method coupled with augmented space recursion (ASR) in conjunction with orbital peeling (OP) technique has been employed to extract the concentration dependent effective pair interactions. Further, the mean-field statistical mechanics based static concentration wave (SCW) model has been used to determine the free energies of these ordered phases as functions of temperature, composition and order parameter. This ASR-OP-SCW approach, applied to Ni-Mo alloy system, gives the correct ground state stability sequence as observed experimentally. Furthermore, it has been shown that such an approach can be used to study the complex transformation behavior involving several competing superstructures as well as competing first order and second order ordering processes.     

大口径厚壁管挤压力理论公式推导、计算机模拟与验证

应用新的力学模型(镦粗式力学模型)推导出大口径厚壁管垂直挤压的挤压力理论计算公式,并与其它力学模型下导出的公式相比较.该公式能够反映挤压力与挤压高度之间的函数关系,而其它公式则不能.同时,还对该公式进行了计算机模拟,模拟表明:利用镦粗式力学模型推导出的公式与模拟结果基本一致,也与生产实际相符.该力学模型更符合大口径厚壁...     

A mathematical model of rough surface contact characterization in spot welding

0ＩｎｔｒｏｄｕｃｔｉｏｎＧｅｎｅｒａｌｌｙ,ｔｈｅｒｅａｒｅｔｈｒｅｅｃｏｎｔａｃｔｓｕｒｆａｃｅｓｉｎｓｐｏｔｗｅｌｄｉｎｇ ,ｔｈｅｕｐ ｅｌｅｃｔｒｏｄｅ/ｓｈｅｅｔｉｎｔｅｒｆａｃｅ ,ｔｈｅｓｈｅｅｔ/ｓｈｅｅｔｉｎｔｅｒｆａｃｅ (ｆａｙｉｎｇｓｕｒｆａｃｅ)ａｎｄｔｈｅｄｏｗｎ ｅｌｅｃｔｒｏｄｅ/ｓｈｅｅｔｉｎｔｅｒｆａｃｅ.Ｏｎｏｎｅｈａｎｄ ,ｔｈｅｃｏｎｔａｃｔｒｅｓｉｓｔａｎｃｅａｔｔｈｅｓｈｅｅｔ/ｓｈｅｅｔｆａｙｉｎｇｓｕｒｆａｃｅｉｓｔｈｅｍａｉｎｆａｃｔｏｒｏｆｔｈｅｏｒｉｇｉｎ…     

Damage analysis and cracking model of reinforced concrete structures with rebar corrosion

The damage of concrete cover in reinforced concrete structures induced by reinforcing steel corrosion is investigated in this study. The damage process of the concrete cover can be divided into two distinct stages: the non-cracking stage and the partial cracking stage. An analytical model based on damage mechanics and elastic mechanics is developed to predict the concrete cracking due to steel corrosion. Based on this model, the expansive pressure and the radial loss of steel bar are discussed. Parametric studies are carried out to examine the effects of the correlative factors on the expansive pressure and the steel loss.     

ZLK15装载机动臂横梁的计算方法研究

装载机由于工作过程循环往复,负载情况经常发生变化,因而其工作装置中各构件常常发生破坏,其中破坏最严重的是横梁.本文首先通过横梁的连接特点和受力条件建立了横梁的力学模型,然后从横梁的几何尺寸、材料强度、使用频率、应力水平等方面进行了详细研究,得出该构件可以用线弹性断裂理论进行力学计算和分析,并根据材料厚度与断裂韧度的关系得出横梁的计算属于平面应力问题的结论.     

连续介质流变理论及其在岩层下沉动态过程中的应用

将连续介质力学理论与流变力学原理统一起来，研究了地表下沉的动态变化过程，并引用薄板弯曲的工程理论，建立了一个岩体实际层状分布的计算模型。此外还在考虑岩体流变特性的同时，进一步探讨了近水平煤层开采引起地有下沉积的动态分布规律。     

氢渗透引起金属膜的塑性形变

将板壳力学、弹塑性力学、热应力理论与金属-氢相互作用理论相结合,讨论了氢进入金属柱形薄膜后晶格膨胀产生的弹性应力、塑性应力和残余应力及这些应力对氢分布和输运、材料性质的影响.结果表明,塑性区中氢的扩散变慢,残余应力改变了样品局域的吸氢热力学性质;在充氢过程中,只有小的充氢流才可能避免材料的塑性损伤.该结果可为氢的提纯、同位素分离以及氢的贮存与输运等应用提供参考.     

局部腐蚀作用下设备的寿命预测

综术字局部腐蚀和应力腐蚀破裂及点腐蚀作用下设备寿命预测技术的进展,由于局部腐蚀萌生、发展具有的内在的随机特征,以及设备长期服役过程中材料,环境等因素波上入的随机干扰,使得单一腐蚀微缺陷具有随机特征,需引入统计方法研究偶然性缺陷群体作用对材料宏观性能的影响。进行局部腐蚀设备寿命预测时,力学研究中对损伤演化及突变的处理方法值得借鉴。     

圆柱磁致伸缩棒在交变磁场中的力学行为研究

以设计的超磁致伸缩换能器的实物模型为基础,建立了换能器的轴对称的有限元模型,对主要在磁-机耦合场作用下,其中的超磁致伸缩棒在交变磁场中的力学行为进行有限元分析,从而为超磁致伸缩换能器的深入研究提供了依据.     

Generalized modeling of chip geometry and cutting forces in multi-point thread turning

A generalized mechanics model of multi-point thread turning operations is presented. The cross section of the chip is determined from the thread profiles of the current and previous teeth as well as the infeed settings of the tool. The chip is discretized along the cutting edge, and the cutting force coefficients are evaluated for each element considering the varying effective oblique cutting angles and chip thickness. The nonlinear Kienzle force model is used to account for the effect of edge radius at low chip thickness values. Total cutting forces are obtained by resolving the elemental forces in the insert coordinate system, and integrating them along the engaged teeth. The experimentally validated generalized mechanics model can be used to predict the chip and cutting load distributions for multi-point inserts with custom thread profiles and infeed plans. The model can be used for both process planning and insert design.     

Damage evolution of metallic materials during high temperature plastic deformation

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｄａｍａｇｅｅｖｏｌｕｔｉｏｎｍｏｄｅｌｏｆｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｐｌａｓｔｉｃｄｅｆｏｒｍａｔｉｏｎｉｓｄｅｒｉｖｅｄｉｎｔｈｉｓｐａｐｅｒｂｙｕｓｉｎｇｓｏｍｅｂａｓｉｃｃｏｎｃｅｐｔｓ ,ｐｒｉｎｃｉｐｌｅｓａｎｄ     

球墨铸铁螺旋孔型斜轧贴皮现象的力学研究

球墨铸铁的螺旋孔型斜轧的生产中出现了贴皮等在轧制钢类材料时不会出现的问题。本文建立了发生贴皮现象部位的力学模型 ,并提出了相应的金属表面切应力的算法 ,作为球铁磨球斜轧中防止贴皮现象的设计准则之一。从力学角度建立起解决贴皮现象的理论基础 ,一方面 ,充实了球墨铸铁轧制工艺的理论基础 ,另一方面 ,也为工程人员提供了理论设计依据。     

On the mechanics and material removal mechanisms of vibration-assisted cutting of unidirectional fibre-reinforced polymer composites

This paper aims to reveal the material removal mechanisms and the mechanics behind the vibration-assisted cutting (VAC) of unidirectional fibre reinforced polymer (FRP) composites. Through a comprehensive analysis by integrating the core factors of the VAC, including fibre orientation and deformation, fibre–matrix interface, tool–fibre contact and tool–workpiece contact, a reliable mechanics model was successfully developed for predicting the cutting forces of the process. Relevant experiments conducted showed that the model has captured the mechanics and the major deformation mechanisms in cutting FRP composites, and that the application of ultrasonic vibration in either the cutting or normal direction can significantly decrease cutting forces, minimise fibre deformation, facilitate favourable fibre fracture at the cutting interface, and largely improve the quality of a machined surface. When the vibrations are applied to both the cutting and normal directions, the elliptic vibration trajectory of the tool tip can bring about an optimal cutting process. There exists a critical depth of cut, beyond which the fibre–matrix debonding depth is no longer influenced by the vibration applied on the tool tip.