关于瞬态应力强度因子和裂纹扩展加速度之间的关系探讨

将动态焦散线法与高速摄影技术相结合,本文记录了高分子材料悬臂梁内裂纹扩展加速、减速过程。一方面,利用动态焦散线可确定扩展裂尖的瞬态应力强度因子;另一方面,利用最小二乘法将裂纹扩展的水平、垂直位移分量拟合成时间(t)的四次多项式,描述了裂纹扩展方向、裂纹扩展加速度以及裂纹扩展加速度与动态应力强度因子的关系。结果表明:裂纹扩展加速度与动态应力强度因子之间存在一定的依赖关系;利用最小二乘法将裂纹扩展的水平、垂直分量拟合成时间(t)的四次多项式,可以对裂纹的扩展方向、加速度进行定量分析。     

ON THE EQUIVALENCE OF STRESS INTENSITY AND ENERGY APPROACHES IN BRIDGING ANALYSIS

Abstract— Through-thickness reinforcement is effective in suppressing delamination in composite laminates. It provides bridging in the crack wake during delamination crack growth. The closure traction behind the crack tip due to this bridging increases the delamination toughness significantly. The effect of bridging may be analysed using the stress intensity approach or the Griffith energetic approach. In this paper, delamination crack growth resistance K _R,(Δa) of a double-cantilever-beam specimen, with through-thickness reinforcement, under Mode I delamination is determined using these two approaches. Additionally, the J-integral analysis is also employed. A comparison between the theoretical results predicted by these three methods is provided using the example of stitched CFRP.     

THE STRESS INTENSITY FACTOR OF SMALL CRACKS AT NOTCHES

Abstract— It was found in a previous publication that stress fields around notches are quantitatively very similar, if the peak stress at the notch root (σ_peak) and the notch root radius ( ρ ) are the same. As a consequence, small cracks (length l ) should have the same stress intensity factor, if σ_peak and ρ are similar. This implies that the geometry factor C in
should primarily depend on l/ρ only, and not on other dimensions. Available data on calculated K values was analysed, which confirmed the similarity concept. An equation for C as a function of l/ρ was obtained. It was shown that K -values calculated with this equation are an accurate approximation for the stress intensity factor of small cracks at notches.     

应力强度因子的误差评估

该文根据裂纹尖端位移的计算公式,导出了一个用于评估应力强度因子计算误差的指标参数。在已知裂纹尖端位移场的情况下,该参数可以有效的说明应力强度因子的计算精度。最后通过算例分析说明该参数是一个有工程应用价值和计算简便的参数。     

PC合金相容性与制品冲击强度关系研究

用TEM、DSC、FT－IR等方法对PC（聚碳酸酯）／PBT（聚苯并噻唑）、PC／PA（聚酰胺）合金的相容性和冲击强度的关系进行了研究。结果表明，分散相在连续相中分散均匀，相畴尺寸适中，共混树脂之间无明显酯交换的合金，只存在1个玻璃化转变温度Tg合，其值低于作为连续相PC的Tg而高于作为分散相的PBT和PA的Tg值，该合金的耐溶剂性能好，冲击强度也高。     

复合材料纤维内含圆盘状裂纹的应力强度因子

复合材料的纤维内含裂纹是造成纤维断裂的一个重要因素。本文采用轴对称多介质问题的边界元方法来分析纤维内含圆盘状裂纹的应力强度因子,以及基体和纤维的模量比、体积比和泊松比等参数对应力强度因子的影响。其分析结果为复合材料纤维断裂形式的破坏机理提供了参考依据。     

两种材料界面裂纹的应力强度因子

选用复变函数的幂级数作为应力函数,分析在两种材料界面上存在裂纹的情况。利用裂纹自由表面力的边界条件及材料界面上的连续条件求得特征值及待定系数之间的关系式,从而求得应力、位移及应力强度因子表达式。本文修改了Lin[1]和Mar[2]的应力函数表达式,使所得应力、位移表达式与Williams[6]及Sih—Rice[3,4]结果一致。基于上述解析解建立了裂纹尖端的奇异元。并以含有界面中心裂纹平板拉伸情况作为计算实例。      

CALCULATION OF THE STRESS INTENSITY FACTOR AND ESTIMATION OF ITS ERROR BY A SHAPE SENSITIVITY ANALYSIS

Abstract— The precision with which the stress intensity factor (SIF) can be calculated from a finite element solution depends essentially on the extraction method and on the discretization error. In this paper, the influence of the discretization error in the SIF calculation was studied and a method for estimating the resulting error was developed. The SIF calculation method used is based on a shape design sensitivity analysis; this assures that the resulting error in the extracted SIF depends solely on the global discretization error present in the finite element solution. Moreover, this method allows us to extend the Zienkiewicz-Zhu discretization error estimator to the SIF calculation. The reliability of the proposed method was analysed solving a two-dimensional problem using an h -adaptive process. Also the convergence of the error with the h -adaptive refinement was studied.     

A NOTCH INTENSITY FACTOR APPROACH TO THE STRESS ANALYSIS OF WELDS

In the context of linear elastic stress gradients that are present in welded joints, a stress field approach based on notch stress intensity factors is presented with the aim of describing stress distributions in the neighbourhood of weld toes, since fatigue strength is dependent on such distributions. This paper summarizes the analytical fundamentals and gives an appropriate definition of the parameters for stress components under opening and sliding modes. Then, by comparing the expected results with those obtained by numerical analysis, the contributions of the symmetric and skew-symmetric loading modes are quantified for different geometries, and summarized into concise expressions which also take into account the influence of the main geometrical parameters of the welded joint. The range of validity and the application limits of this field approach in the presence of weld toe radii are discussed. Finally, a synthesis of experimental fatigue strength data based on the new field parameters is reported.     

卡诺制冷机的火用损率与制冷系数间的关系

在文献[4-7]的基础上，本文导出了卡诺制冷机的Yong损率与制冷系统间的关系，并且分析了各种因素对该关系的影响。     

THRESHOLD STRESS INTENSITY BEHAVIOUR OF CRACKED STEEL STRUCTURAL COMPONENTS

Abstract— The effects of stress variables on the fatigue design of steel structural components (SAE 1010 steel) in the threshold region are investigated. The threshold and the closure threshold stress intensity ranges both decreased linearly as the stress ratio is increased. The threshold and opening threshold stress intensities also decreased linearly as the magnitude of compressive peak stress is increased. Crack opening stress measurements using a mechanical extensometer showed that the crack is not fully closed throughout the stress cycle at the threshold level. The crack opening stress is found to be independent of the crack length up to a certain crack length depending on the loading conditions. It is also found that the threshold stress intensity consists of two components: opening or closure stress intensity required to overcome crack closure, and intrinsic stress intensity range required to grow the crack. Linear relationships are obtained for the intrinsic stress intensity range as a function of stress ratio or compressive peak stress.     

有限变形理论能量释放率增率形式

基于有限变形理论中的能量原理和变分原理,考虑以有裂纹的瞬时位形为参考,建立增量变形引起的裂纹扩展方程能够更真实的描述裂纹尖端的扩展机制,在含有裂纹物体的瞬时变形的基础上,推导了裂纹体的能量释放率和增率的形式,提出了裂纹扩展判据.该判据反映了单位时间内裂纹扩展单位面积可以提供的能量与单位时间内裂纹扩展单位面积所需要的能量...     

EFFECTS OF CRACK CLOSURE AND MEAN STRESS ON THE THRESHOLD STRESS INTENSITY FACTOR FOR FATIGUE OF AN ALUMINIUM CASTING ALLOY,

Abstract— Observations have been made of the threshold fatigue properties of an Al-Mg-Si casting alloy. First, it has been shown that there exists a critical value of the stress ratio, R , below which the threshold stress intensity factor decreases with increasing R but above which it is constant. Second, measurements of the cyclic crack opening displacement have been used to examine crack closure effects and to deduce the effective cyclic stress intensity factor. The two sets of data are compared with existing models for threshold phenomena.     

熔体流动速率与温度关系的初步探讨

利用熔体流动速率仪研究了PP、LDPE、PS、ABS的流变性能，讨论了温度(T)对熔体流动速率(MFR)的影响。结果发现，温度升高，MFR随之增大，且MFR与1／T成指数关系。     

受限空间中固体可燃物的热释放速率

采用基于耗氧原理的燃烧热释放速率测量方法和锥型量热计系统。在不同的外加辐射热作用下测量了PMMA和松木两种典型固体可燃物的热释放速率，分析了PMMA与松木燃烧过程以及外加辐射热对固体可燃物热释放速率的影响，发现固体可燃物的燃烧放热过程与它们本身的结构特性密切相关，外加辐射热对固体可燃物的热释放速率有很大的影响。     

纤维—基体界面脱粘能量释放率

研究一个纤维拔出界面脱粘断裂能量释放率分析的简单模型，给出纤维－基体界面断裂能ＧⅡ工程计算公式的推导过程，用有限元法检查了该公式的可靠性与适用范围，并提出一个修正表达式。     

纤维─基体界面脱粘能量释放率

研究一个纤维拔出界面脱粘断裂能量释放率分析的简单模型，给出纤维－基体界面断裂能ＧⅡ工程计算公式的推导过程．用有限元法检查了该公式的可靠性与适用范围．并提出一个修正表达式     

THE EFFECT OF SPECIMEN SIZE ON THE CTOD R-CURVE BEHAVIOUR OF A TITANIUM ALLOY

Abstract— —This paper presents preliminary results from a large experimental programme to study geometry and size effects in CTOD R-curves. The results presented were obtained from unloading compliance R-curve tests performed at room temperature on different sized single-edge-notch bend specimens made from Ti–3Al–2V alloy. The crack growth resistance was measured in terms of both the conventional CTOD, δ₀, (i.e. as defined in BS 5762) and CTOD corrected for crack growth, δ_R . It was found that the δ₀ and δ_R R-curves were independent of specimen size up to crack extensions corresponding to approximately 10–15% of the original uncracked ligament. Also, after crack extensions of 30–40% of the initial ligament the δ₀ and δ_R R-curves exhibited well defined upswings. The upswing in the CTOD R-curves is thought to be a result of a reduction in crack tip constraint.     

焊接技术与聚氯乙烯薄膜塑化度的关系EI

聚氯乙烯组分和薄膜厚度的改变将使焊接点最大强度和热合参数发生变化,并且可用方程来进行说明。本文用不同量的邻苯二甲酸二辛酯(DOP)进行实验,结果表明:焊接参数与具有不同塑化度的高频热合聚氯乙烯薄膜的最大接缝强度相对应。