基于静力学分析与静扭试验的变速器壳体强度研究

以某轻型载货汽车变速器铸铝壳体为研究对象,应用有限元静力学方法分析其在1挡工况下的壳体强度,通过对ANSYS Workbench后处理数据进行分析,得出变速器壳体应力、变形的分布情况。并通过静态扭矩加载实验,测得铸铝壳体的应力、应变情况,由此可获得该铸铝壳体在实际工作状态下的应力应变状态。测试分析结果与静力学分析结果的比较,为有限元模型的修改及变速器壳体的进一步优化提供了依据。     

Oblique impact on a head-helmet system

The propagation of waves produced by pendulum impact both radially and obliquely on two different models simulating a head-helmet system was studied experimentally by means of strain gages attached to the surfaces of the components representing the skull and the helmet and by tourmaline crystals embedded in a gel representing the brain. The first model consisted of a set of nested aluminium and styrofoam full or partial spherical shells, while the second comprised an actual cadaver skull held in an army helmet by means of a polyurethane foam. The results were compared with theoretical and experimental information previously developed.     

基于高温铸坯黏弹塑性的坯壳动态鼓肚研究

基于高温铸坯材料黏弹塑性本构方程,建立了坯壳动态鼓肚数学模型。根据坯壳不同的初始状态与变形历史确定了两种边界条件。利用模型计算坯壳鼓肚变形,并与实测数据进行对比,验证了理论解的正确性以及模型的有效性。根据鞍钢工业板坯连铸机的设备工艺参数,分别计算了刚出结晶器的坯壳和远离结晶器的坯壳的鼓肚变形曲线,以及坯壳在固液交界面处的应变与应变速率。分析了铸坯坯壳在铸机扇形段内的鼓肚变形与应变变化规律,并讨论了辊间距、     

水压胀合高压釜衬里的力学模型及试验研究

探索一种新的液压胀合技术——水压胀合法，并评估其贴合效果。水压胀合法是利用高压釜整体水压试验时的压力来胀合衬里，使衬里产生塑性流动，达到全部或部分消除衬里与壳体之间的初始间隙。按照弹——塑性理论推导出力学模型，通过实测层间间隙、应力和应变来评估其贴合效果。结果表明：理论计算值与实测结果基本一致，最大误差为13．8％；尽管最大的初始间隙达16mm，但经胀舍处理后残余间隙仅在0．6～0．9mm之间；壳体材料在升压循环过程中处于弹性范围内，在内压大于3．1MPa时，衬里和壳体基本变为一体化材料，应力与内压力的线性相关系数大于0．99。     

基于等刚度条件的薄壁结构的一种材料替代轻量化设计分析方法

通过对板壳结构有限单元的弯曲应变能和膜应变能进行分析,得到一个采用不同材料的薄壁结构的刚度之间的近似解析关系式。将其与结构刚度的有限元计算分析过程相结合,提出一种不同材料但等刚度的薄壁结构的迭代设计方法和材料替代轻量化分析方法。分析得到的薄壁结构关于板壳的弯曲应变能占总的应变能的比例  的等刚度曲线,可用于直观地评价材料替代得到的等刚度结构的轻量化效果,可指导薄壁结构的轻量化设计。分析表明,材料替代对薄壁结构刚度的影响不仅与材料的弹性特性和板壳厚度相关,还与给定载荷下结构的  参数相关。对于铝板替代钢板的薄壁结构设计问题, 越高,则等刚度铝板结构的轻量化效果越明显。通过对一个悬臂薄壁钢板曲梁结构和一个典型车身接头结构的材料替代设计和轻量化分析,验证了提出的设计、分析方法的有效性和结论的正确性。     

Micro-strain distribution around a crack tip by electron beam moiré methods

The microscopic deformation around a crack tip in a small tensile specimen of aluminum was measured by using electron beam moiré methods. The tensile test was carried out in a scanning electron microscope(SEM) by using specially designed small tensile testing apparatus for an SEM. A line grating with a pitch of 87 nm was written at the crack tip by electron beam lithography. SEM images of the grating contained(original) moiré fringes at certain magnifications without loadings on the specimen. The displacement and strain in the region 10 to 50 μ m from the crack tip were evaluated by analyzing the (mismatch) moiré fringes. Measured strains normal to loadings(longitudinal strains) near the crack tip were found to be comparable to those estimated using linear elastic fracture mechanics(LEFM), for the lowest load, and elastic-plastic fracture mechanics, at effective crack tip position located within the actual crack tip. The exponent of the strain singularity in the vicinity of the actual crack tip changed with applied stress, ranging between ?0.64 and ?1.0. The measured crack tip opening displacement(CTOD) values disagreed with CTODs based on the Hutchinson-Rice-Rosengren(HRR) field, the Dugdale model, and LEFM. The experimental plastic zones spread from the line of crack extension up to an angle of about 60°, as expected from LEFM theory.     

Development and experimental validation of a three-dimensional finite element model of the human scapula

A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.     

铝硅基精铸材料薄壁壳体成型多尺度分析

针对铝合金薄壁壳体铸造成型高质量要求,通过向ZL101A铝合金中增添Al-10Sr变质剂以及微量Ni元素,制备铝硅基精铸材料坯件,借助加热设备与SCC-44500电子万能试验机对铝硅基精铸材料进行高温压缩试验,得到不同应变率与不同温度下材料的应力-应变曲线,发现铝硅基精铸材料在各应变率及温度下的屈服强度相对ZL101A铝合金均提高。以铝硅基精铸材料进行液压泵薄壁壳体铸造工艺设计分析,基于ProCAST铸造模拟软件,采用低压铸造工艺方案对铝合金薄壁壳体低压铸造过程进行多尺度模拟,分析预测得到了温度场和流动场对铸件充型和凝固过程中缩孔缩松形成的影响,并对壳体铸件的显微组织特征进行了分析,观察得到内部二次枝晶臂间距和共晶层片间距分布状态,综合分析宏微观结果可知,适合的铸造工艺可以制备出完整高性能的铝硅基合金薄壁壳体铸件。     

Dry Sliding Wear Behavior of Palmyra Shell Ash–Reinforced Aluminum Matrix (AlSi10Mg) Composites

High strength, light weight, ease of fabrication, excellent castability, and good wear resistance make aluminum alloy composites suitable for commercial applications. In this work, a silica-rich ash particle (palmyra shell ash) was reinforced with aluminum alloy (AlSi10Mg) composites and its mechanical and tribological properties were studied. The aluminum alloy was reinforced with 3, 6, and 9 wt% of palmyra shell ash particles, and its dry sliding wear behavior was studied using a pin-on-disc machine under different loading conditions. The result shows that the dry sliding wear resistance of Al–palmyra shell ash composites was almost similar to that of fly ash– and rice husk ash–reinforced Al-alloy composites and these composites exhibit better wear resistance compared to unreinforced alloy. The palmyra shell ash particle weight fraction significantly affects the wear and friction properties of the composites. Scanning electron microscopic examination of the worn surface reveals that at various loads palmyra shell ash particles act as load-bearing constituents and the wear resistance of the reinforced palmyra shell ash with a size range of 1–50 µm was superior to that of unreinforced alloy. Mechanical properties (hardness and tensile strength) were also studied and it was observed that the reinforced Al-alloy showed a significant increase in mechanical properties.     

盾构机盾尾变形检测与有限元分析

为研究盾构机施工过程中盾尾的实时变形,提出一种有限元分析与应变检测相结合的方法,研发一种盾尾变形检测系统。建立了盾构机简化的三维模型,并依据盾构机在施工过程中,其壳体的受力与变形情况,通过有限元仿真得到盾尾应力与变形之间的本构关系,结合现场具体情况,确定了应变花的粘贴位置和数量。利用变形检测系统测量了盾尾 2 个截面上共 12 个区域的变形数据,并与现场全站仪测量数据进行了对比,两者之间的差别平均为 2.6 mm 。     

热带钢连轧多场耦合演变过程有限元分析

根据物理冶金组织演变规律和经验公式，开发了金属热变形过程耦合组织演变的计算模块。结合某厂2050热带钢连轧工艺过程，利用非线性刚塑性有限元法，建立热连轧过程热、力、组织的多参量耦合仿真模型。运用该模型对2050现场实际轧制过程进行模拟计算，分析了轧制过程轧件变形场、温度场及显微组织的演变规律。模拟得到的轧制力能参数、温度、组织分布与实测数据基本一致。     

A continuum plasticity model for the constitutive and indentation behaviour of foamed metals

A yield surface is proposed that can be fitted to the plastic flow properties of a broad class of solids exhibiting plastic compressibility and different yield points in tension and compression. The yield surface is proposed to describe cellular solids, including foamed metals, and designed to be fitted to three experimental results: (1) the compressive stress–strain response (including densification), (2) the difference between the tensile and compressive yield points and (3) the degree of compressibility of the foam, as measured by the lateral expansion during a uniaxial stress compression test. The model is implemented using finite elements and used to study the effects of plastic compressibility on two problems: the compression of a doubly notched specimen and indentation by a spherical indenter. The model is then fitted to the properties of a typical closed cell aluminum foam and used to study indentation into a dense aluminum face sheet on a foam foundation. The dependence of the indentation load–displacement curve on the relevant material and geometric parameters is determined, and a single load–displacement relation is presented which approximates the behaviour of a wide range of practical designs. These results can be used to design against indentation failure of sandwich panels.     

“1+4”铝热连轧轧制力自学习

在铝热连轧精轧生产过程中,轧制力的预报精度直接影响板厚和板凸度控制精度。针对河南某1+4铝热连轧机现场轧制力预报精度较低的问题,根据现场采集的大量轧制数据,建立了轧制力模型自学习算法,并用细菌觅食优化算法对自学习中的增益系数进行了优化,提高了轧制力预报精度。     

Effects of acetabular resurfacing component material and fixation on the strain distribution in the pelvis

A 3D finite element (FE) model of an implanted pelvis was developed as part of a project investigating an all-polymer hip resurfacing design. The model was used to compare this novel design with a metal-on-metal design in current use and a metal-on-polymer design typical of early resurfacing implants. The model included forces representing the actions of 22 muscles as well as variable cancellous bone stiffness and variable cortical shell thickness. The hip joint reaction force was applied via contact modelled between the femoral and acetabular components of the resurfacing prosthesis. Five load cases representing time points through the gait cycle were analysed. The effect of varying fixation conditions was also investigated. The highest cancellous bone strain levels were found at mid-stance, not heel-strike. Remote from the acetabulum there was little effect of prosthesis material and fixation upon the von Mises stresses and maximum principal strains. Implant material appeared to have little effect upon cancellous bone strain failure with both bended and unbonded bone-implant interfaces. The unbonded implants increased stresses in the subchondral bone at the centre of the acetabulum and increased cancellous bone loading, resembling behaviour obtained previously for the intact acetabulum.     

Different degree of reduction and sliding phenomenon study for three-dimensional hot rolling with sandwich flat strip

Symmetric rolling of 3D sandwich flat strips with thermal-elastic–plastic coupled model was studied under the assumption of an elastic roller and the condideration of heat transfer. Aluminum–copper sandwich flat strips were used in this study.The numerical model of symmetric rolling for 3D sandwich flat strip with thermal-elastic–plastic coupled model was developed based on the large deformation–large strain theory, the update Lagrangian formulation and the incremental principle. Besides, flow stress was considered as the function of strain, strain rate and temperature. The theoretical model of finite element method containing the two-order strain rate formulation acted as the basis for determining the convergence of simulation results.The contact surface between the aluminum and copper for the sandwich flat strip was also discussed. First of all, the contact face between the aluminum and copper was assumed that it would be fixed without sliding. Symmetric hot rolling of the aluminum and copper sandwich flat strip was analyzed. A slide criterion was then introduced to study the shear stress states of the contact face between aluminum and copper of sandwich strip, which was used to compare the relation between the maximum shear stress and the yielding shear stress on the contact face. If the maximum shear stress of aluminum or copper is smaller than the yielding stress of aluminum or copper respectively, sliding does not occur on the contact face. On the contrary, the sliding may occur on the contact face between aluminum and copper.Three different degrees of reduction were simulated in this study to analyze the states of shear stress on the upper aluminum strip and lower copper strip close to the contact face. Finally, it finds that the sliding on the contact face between aluminum and copper may occur around certain degree of reduction. The average rolling force of the simulation result was compared with experimental data [8] to verify the simulation results.     

Pulse transmission in elastic exponential and conical shells

A theoretical and experimental investigation was conducted to ascertain the response of an axisymmetric exponential shell and of a hollow cone with identical terminal dimensions and lengths, both composed of aluminum, to central longitudinal impact by steel spheres. The principal tests were concerned with loading at the small end and an open distal section; in a few cases, the large end was covered by a relatively thin aluminum plate and subjected to central impact by the various strikers. The range of initial velocities for the 3.175, 6.35 and 12.7 mm diameter pneumatically-fired steel spheres was from 7.6 to 60 m/s, while 23.7 and 50.8 mm steel balls were propelled in a pendulum arrangement at about 1.2 m/s. The input was monitored by a quartz crystal, while the waves were detected by a set of foil gages. A one- and a two-dimensional numerical analysis were executed for a typical set of experimental conditions of the first wave transit in both systems when struck at the small end: the results were in good correspondence with experimental data. The exponential shell exhibited the theoretically predicted cut-off behavior beyond a certain pulse duration which was also found previously in the case of a geometrically similar solid exponential rod. Correspondingly, the conical shell evidenced enormous attenuation, but not complete cut-off beyond such critical impact duration when the wave process was initiated at the small end. The much greater dispersion and attenuation relative to that of the solid bars is primarily due to wall bending of the specimens.     

The Role of Aluminum Segregation in the Wear of Aluminum/Bronze-Steel Interfaces Under Conditions of Boundary Lubrication

An interest in the wear of steel nonsteel systems, currently in use in aircraft fuel systems, has led to a study of aluminum bronze sliding on KE961 steel in the presence of kerosene with, and without, the addition of a commercial boundary lubricant. Experiments were conducted to determine wear rates with change of load together with an extensive investigation of the contacting surfaces using physical techniques such as EPMA, SEM and Auger spectroscopy.

It was found that the additive had an initial pro-wear effect on the bronze followed by a sharp reduction in wear. The results of the measurements, and of the surface analysis, indicate that the mechanism responsible for this wear is due to preferential segregation of the aluminum to the surface. In the absence of the additive, aluminum is transferred to the steel and forms a solid solution which can cause seizure to occur.     

基于生死单元法的双辊铸轧过程热-力耦合数值模拟

以二辊160mm×150mm立式铝带实验铸轧机为对象,基于MSC.Marc商用有限元软件及其二次开发接口,引入纯铝固-液两相材料本构模型和界面压力热阻数学模型,建立了双辊铸轧过程热-力耦合非线性有限元模型。采用生死单元法模拟铝液的连续浇入,解决了辊套和铸轧区铝带材间的连续耦合传热问题。通过数值模拟,给出了铸轧速度、浇铸温度、熔池高度等因素对KISS点位置和辊面温度时间历程的影响规律,并对典型工况温度模拟结果进行了实验验证。     

Three-dimensional finite element stress and strain analysis of a transfemoral osseointegration implant

The percutaneous transfemoral osseointegration implant is an alternative technique for direct prosthetic limb attachment. In order to investigate the stress and strain in the transfemoral osseointegration implant system, finite element (FE) analyses were carried out using three-dimensional femur-implant models and the commercial FE software ABAQUS. The three-dimensional femoral model was reconstructed from presurgery CT scans of an above-knee amputee. The implant was then inserted into the femoral model using Boolean operations in CAD software. Under a typical walking load, stress and strain from the femur-implant FE model were investigated. Stress concentrations were found near to the distal and proximal regions of the femur. To study the effect of different contact ratios between femur and implant, FE analyses were carried out using different implant diameters. The results showed that there were local stress variations near the contact discontinuity areas. A comparison was also made between the results of this study and a previous study using axisymmetric FE models. The results of the two studies revealed different stress levels, but good correlation was found in the overall stress distribution.     

仿真与实测多信息融合的机械结构外载荷反演技术

针对机械结构在复杂工况下载荷边界条件难以确定的问题,提出一种仿真与实测多信息融合的外载荷反演技术.首先建立待研究结构的有限元模型,在结构外载荷作用位置施加单位载荷,计算构件全场应变响应;然后基于D-最优设计原则得到应变测试的测点最佳布置方案和最优载荷系数矩阵,据此建立外载荷与应变间的动态响应关系;根据得到的测点布置方案...