TiFe_xM_y氢化物形成焓的数学模型与计算预报

研究了 TiFe_xM_y 合金氢化物(M 代表 Mn,Ni,Co,Zr,Nb,V,Cr 和 Al,x≥0.5,y≤0.3)分解自由能变化△G 与形成热△H 和元素原子参数间的关系。结果表明;氢化物分解时的△G可以用合金组成元素的原子尺寸因素、元素的平均电负性差和平均外层电子数的半经验方程式来表示,并由此可推出氢化物分解热△H,计算预报值与实际值相符,相差在5kJ(mol H_2)~(-1)以内。比较三参数对△H 的贡献大小表明,TiFe_xM_y 合金的△H 主要受电负性差或电子因素控制。     

一个新的接触疲劳寿命预测模型的研究

本文给出了一个新的针对应力控制接触疲劳问题的寿命预测模型。在该模型中，选用Ｍｉｓｅｓ等效应力作为接触疲劳应力控制参量；引进了非零的接触疲劳应力强度值，根据损伤力学理论，分析了接触疲劳应力强度值与基体材料性质，第二相夹杂之间的关系，同时考虑了表面起裂和亚表面起裂两种失效形式，并将对这两种失效形式的寿命预测统一到一个公式中，引进一个与油膜系数Λ有关的系数ｆ（Λ），来表征润滑程度对接触疲劳寿命的影响。应用该模型来预测一些实验的接触疲劳寿命，计算值与实测值吻合很好。     

A STOCHASTIC MODEL FOR THE SIMULATION OF DRAFTING

Drafting is an important process taking place at several stages of yarn manufacturing. We present a stochastic model which describes the interactions of individual fibres and is inspired by the spin flip process used in statistical mechanics. Simulating on the basis of such a model amounts to seeking an approximate solution of a minimal cut problem which is the formulation of a deterministic approach in term of friction forces.     

金属材料高温持久强度的预测模型

在Larson-Miller方程基础上，利用全微分和状态函数特征，建立了金属材料在给定温度条件下持久强度与高温瞬时强度之间关系的数学模型，并成功用于T91耐热钢和GH2871高温合金持久强度的预测。     

A PROBABILISTIC MODEL FOR PREDICTION OF LCF SURFACE CRACK INITIATION IN PM ALLOYS

The Low Cycle Fatigue (LCF) life of PM Ni-base superalloys is commonly reduced by surface crack initiation at ceramic inclusions. For this reason, a probabilistic model has been developed that predicts the size of surface crack initiation sites from the inclusion size distribution. For the experimental correlation of the model two sets of alloys were examined: a “standard” (i.e. as-received) alloy, and a second material of identical composition to which a known distribution of ceramic inclusions was incorporated (or seeded). Model predictions were found to be in excellent agreement with the results obtained from the seeded materials in which the defect size distribution is larger and better characterized, and were satisfactory for the unseeded material in which two types of surface defects (pores and ceramic inclusions) initiate LCF cracks. The results of these experiments were employed in LCF simulations of both test specimens and full scale components. These indicated that differences exist between the site preference for LCF crack initiation in small test specimens and large scale components due to a scale effect. Such results demonstrate the utility of seeding experiments for generation of LCF test data used in component design.     

基于极限分析的三叶墙抗压强度预测模型研究

该文以极限分析法为基础,将有限元塑性极限分析下限法运用于砌体结构三叶墙的抗压强度预测。结合常见受压三叶墙破坏模式,基于材料试验和小型砌体试件试验赋予了本构模型参数。在此基础上,考虑了不均匀压应力边界条件,提出了三叶墙抗压强度预测模型。根据文献的试验数据,利用该模型预测了多个三叶墙的抗压强度,并与试验结果和抗压强度预测公式的结果进行了对比,说明了该模型的准确性。     

用弹道理论模型和Weibull模型预测台阶爆破的爆堆形态

介绍了预测爆堆形态的弹道理论模型和Ｗｅｉｂｕｌ模型，提出了弹道理论的分条方法及抛掷轨道的计算公式。同时将Ｗｅｉｂｕｌ概率分布函数成功地引入爆堆形态的分布计算中，根据实测值提出了爆堆初始高度的修正方法。并以南芬露天铁矿为例进行了验证。     

建筑结构钢超低周疲劳断裂破坏的损伤预测模型

针对地震作用下建筑结构钢的超低周疲劳断裂问题,在单调加载损伤模型的基础上,提出了一种适用于超低周循环加载情况下的损伤预测模型,并借助ABAQUS软件的用户自定义材料子程序模块,将建立的损伤预测模型引入到有限元分析程序中。然后分别依据建筑钢结构母材、热影响区和焊缝金属缺口试样的单调加载和超低周循环加载试验,标定了材料的损伤模型参数,并对比分析了缺口圆棒试样在不同加载方式下的损伤演化规律,损伤分析结果表明缺口圆棒试样的裂纹都产生于试样截面中心处,这与试验结果一致。最后,以钢框架梁柱焊接节点为研究对象,应用损伤模型分析了节点危险部位的损伤演化规律,数值模拟了节点的超低周疲劳断裂破坏过程,最终得到节点的疲劳寿命与试验结果吻合良好。     

A CHANCE-CONSTRAINED MODEL FOR THE OPERATION OF THE ASWAN HIGH DAM

This paper analyzes the problem of the operation of Aswan High Dam. A chance-Constrained Model (CCM) is developed for the operation of the Dam. The model optimizes total benefits from the discharged water while incorporating all physical and operational constraints. Zero-order decision rules are used to obtain the model deterministic equivalent. The model operating policy is compared with the current operation policy derived from a heuristic rule and an alternative policy derived from a dynamic programming model developed earlier for the operation of the Aswan High Dam. The chance-constrained approach provides a natural and more flexible model for the operation of the Dam.     

考虑细观组分影响的混凝土宏观力学性能理论预测模型

混凝土宏观力学性能与其内部细观结构构造密切相关。该文建立了一类能够考虑细观组分影响的混凝土宏观力学性能理论预测模型。首先,采用细观力学数值试验法对理论模型中的参数进行了标定;进而,基于该模型对混凝土断裂能和单轴抗拉强度在材料层次的尺寸效应行为进行了分析。结果表明：混凝土断裂能和单轴抗拉强度均随骨料级配（即最大骨料粒径）发生变化,且受到界面特性的影响。当界面过渡区力学性能相对薄弱时,混凝土强度较低,断裂能和单轴抗拉强度随骨料级配增大而呈现减小的趋势;当界面过渡区力学性能较强时,混凝土强度较高,断裂能和单轴抗拉强度随骨料级配增大亦呈现增大的趋势。计算结果与试验结果吻合良好,验证了该文建立的理论预测模型的准确性和合理性。     

有限元网格图自动生成算法

本文在有限元网格图拓扑分析的基础上,讨论了单元节点拓扑阵自动生成方法和整体节点拓扑阵自动组集方法,并给出了算法。这种方法实现了2D和3D有限元网格图完全自动生成过程,并为单元及节点的相关性分析提供了依据。     

含空孔直眼掏槽爆破效果分析模型

直眼掏槽是隧道掘进深孔爆破中的关键技术 ,炮孔深度对掏槽爆破效果有重要影响。本研究通过建立槽腔内抛体运动的二相流力学模型 ,揭示了炮孔深度影响掏槽效果的物理本质 ,阐述了炮孔深度对掏槽效果的影响规律 ;为含空孔直眼掏槽爆破参数设计提供了依据。理论分析结果与工程实践相吻合。     

BMI树脂化学流变模型及RTM工艺窗口预报研究

研究用于航空结构复合材料的RTM工艺专用双马来酰亚胺树脂(BMI)体系化学流变特性,并建立其双阿累尼乌斯流变模型。模型对树脂粘度的模拟结果与实验结果具有良好的一致性。所建立的粘度模型可有效模拟该树脂在不同工艺条件下的粘度行为,准确预报树脂体系的低粘度工艺窗口,为优化RTM工艺参数和保证产品质量提供必要的科学依据。      

预测低合金钢试样破坏的弹塑性断裂模型

该文建立了预测低合金钢结构断裂破坏的弹塑性断裂理论与模型。将两个独立判据——强度及韧度准则联系起来,搭起结构特性与材料参数间的纽带桥梁：可由处于弹塑性断裂控制的小尺寸低合金钢试样的结构特性确定其材料参数;基于确定的材料参数,可建立起预测低合金钢结构破坏的全过程曲线。该文进行了多组相同尺寸而不同裂缝长度的Q345B钢的单边拉伸试验,基于所提模型及试验结果,确定出无尺寸效应的断裂韧度、屈服与极限强度等材料参数;进而构建了可涵盖所有试验点的Q345B钢的安全设计曲线（±10%界限）。研究成果可为确定金属材料参数及预测金属结构破坏提供新思路。     

钢筋粘结滑移弯矩-转角计算模型

纵筋在梁-柱或基础-柱界面处滑移将使侧向变形出现显著的增加。该文在现有二折线型钢筋粘结滑移弯矩-转角骨架曲线基础上,提出了屈服点以及破坏点滑移转角计算方法,可以用于预测滑移造成的侧向变形。根据与相互独立的五批共24个圆柱试验结果对比,其计算结果具有较高的精度。在OpenSees软件中用基于力的纤维单元与粘结滑移弯矩-转角模型,对不同圆柱低周反复试验进行数值模拟,发现该模型计算结果与试验结果吻合很好。进一步,对圆柱在地震波作用下的振动台试验进行时程分析,柱顶位移和柱底滑移变形都能得到很好的预测。进行参数分析,结果表明极限点滑移量在总变形中的占比约为30%~40%,该占比随轴压比增加而减小,随体积配箍率减小而减小。     

风雪绕流数值模拟的积雪预测模型研究

为研究钝体风雪绕流效应下的地表积雪现象,根据壁面剪切机制及空间混合理论共同确立了积雪预测模型,采用欧拉框架单流体方法对1 m高度立方体模型周边的风雪两相流动情况及空间雪相浓度进行了求解。通过对比不同积雪模型下沉积预测指标在绕流区域的分布情况,及以此得到的积雪预测形态与实测结果的差异发现：该文采用的积雪模型不完全依赖于当地摩阻风速与临界起动风速的相对关系,一定程度上避免了模型参数的取值局限,对沉积现象的反映更为直观;由于综合了两套理论并引入沉积量估计的双重动态指标,该文对于雪面侵蚀及沉积区域的界定划分较为清晰,对积雪形态的预测包括雪面极值位置的捕捉、坡面起伏规律的再现,都较已有数值计算结果更为合理。模型方法可用于其他外形地物绕流下的地表积雪现象模拟。     

A MECHANISTIC-BASED THERMOMECHANICAL FATIGUE LIFE PREDICTION MODEL FOR METAL MATRIX COMPOSITES

The framework for developing a mechanistic-based life prediction model for metal matrix composites is described. For a composite consisting of unidirectional silicon carbide fibers in a titanium aluminide matrix, SCS-6/Ti-24A1-1INb (at%) [0]₈, three dominant damage mechanisms were identified: (1) matrix fatigue damage, (2) surface-initiated environmental damage, and (3) fiber-dominated damage. Damage expressions were developed for each mechanism along with a method for determining the constants. The damage is summed to obtain the total life. The model is capable of making predictions for a wide range of histories, including isothermal fatigue at different frequencies and stress-ratios, thermomechanical fatigue (TMF) under in-phase and out-of-phase cycling conditions, thermal cycling at constant stress, and stress holds at either maximum or minimum stress. Considering the wide range of cyclic conditions, the predictions compare favorably with experiments. In addition, the controlling damage mechanism for each history is predicted.     

THEORY OF THE FRACTIONAL COLLECTION EFFICIENCY FOR THE AXIAL FLOW CYCLONE DUST COLLECTOR

A cyclone dust collector is a simple device with no moving parts, so it is applied in many industrial fields. However there is still no satisfied theory to estimate the collection efficiency for a given cyclone with high reliability since it is very difficult to predict the movement of the fine solid particles in the three dimensional turbulent rotational flows in the cyclone. A new model of the fractional collection efficiency including the diffusion effect of the solid particles and the decay effect of the tangential velocity of gas flow along the concave wall surface has been derived. In order to confirm this model, a simplified axial flow cyclone of body diameter D₁ = 99 mm has been constructed and fly-ash particles were used as a test dust. The experimental results of collection efficiency were compared those predicted by the Ogawa model and the Fuchs model.     

PREDICTION OF THE FATIGUE THRESHOLD FOR A CRACKED BODY USING SHAKEDOWN THEORY

Abstract— In this paper, the fatigue threshold Δ K _th of a cracked body is studied. Unlike other approaches given in the literature, the shakedown theory is used for predicting Δ K _th. A crack is considered as a sharp notch, the radius of which, at the threshold stress level, is a material constant. The threshold of crack propagation is explained as being due to shakedown of the cracked body, and a simple but reasonable model is derived. The value of Δ K _th is found to be proportional to the yield stress multiplied by the square root of the effective crack tip radius. Using this model, Δ K _th is calculated for some materials. Comparison of the predicted fatigue thresholds with those obtained by experiments, or by using other approaches, indicates that our model provides satisfying results.