加载速率对焊接接头断裂行为的影响

在不同温度、不同加载速率下，对典型建筑结构用钢及其焊缝进行拉伸试验，测试其基本力学性能。采用能综合考虑加载速率及高加载速率下材料温度变化的R参量，确定本构关系。通过断裂力学试验，测试不同温度及加载速率下供试钢材及其焊接接头的断裂韧度值。随加载速率的增大，断裂韧度降低，但存在有较大的分散性。不同加载速率下裂纹尖端应力场数值分析结果表明，裂纹尖端最大主应力随加载速率的增大而升高。最后基于局部法，研究不同加载速率下母材及接头的断裂行为。局部断裂参量－－威布尔应力不受温度、加载速率的影响，可有效地描述材料的断裂行为。     

应用局部法预测焊接接头动态断裂性能

在不同温度、不同加载速率下进行了典型钢结构用钢拉伸试验，采用能综合反映加载速率和高加载速率下材料温升的R参量来描述材料的本构关系。通过理论分析和试验研究，讨论了加载速率和温度对钢结构用钢及其焊接接头断裂行为的影响，采用基于概率断裂力学的局部法，由静载断裂试验结果对高加载速率下接头断裂行为进行了成功预测。     

非均质焊接接头断裂行为预测研究

基于局部法定量研究了焊接接头中强度匹配、试样几何形式对接头断裂行为的影响。首先由标准三点弯曲试样的断裂韧度值,得出反映材料脆性断裂的控制参量,再根据该参量对不同接头强度匹配下三点弯曲和双边裂纹拉伸试样的断裂行为进行了定量预测,当考虑由于延性裂纹扩展所造成的应力升高后,其结果与试验结果相当吻合。表明局部法能很好地描述材料的断裂行为。     

局部热处理对TA1钛合金-SPCC钢压印接头失效行为的影响

在自行搭建的局部热处理试验平台上将TA1钛合金-SPCC钢压印接头连接部位加热至900℃水淬,研究了局部热处理对此压印接头失效载荷和失效模式的影响。结果表明:局部热处理后该压印接头的失效载荷为5 371.9N,比未经热处理的(4 252.4N)提高了26.34%;未经热处理压印接头的失效模式为上下板拉脱失效,断裂方式为韧性断裂,局部热处理后该压印接头的失效模式为拉脱+颈部断裂混合失效,断裂方式为准解理断裂。     

焊接接头脆性断裂评定的局部法研究进展

介绍了几种焊接结构断裂行为预测和评定方法的局限性。从理论基础、微观理论基础、评定方法等方面详细论述了焊接接头脆性断裂评定的局部法，并介绍了国内外研究状况及最新进展。指出研究各种塑性损伤模型在焊接接头中的可行性，探讨符合焊接接头特点的塑性损伤模型及控制参量的必要性。分析塑性损伤对Beremin解理断裂模型局部断裂参量的影响，进而利用局部法对焊接接头的脆性断裂行为进行科学预测。     

飞机结构强度试验局部约束装置设计

采用加载夹具对中央翼接头加载过程中,由于中央翼发生航向变形,垂向和侧向载荷在航向产生载荷分量,容易对接头造成损伤。因此设计一种局部约束装置,通过卡板把该装置安装在中央翼上,限制夹具与接头之间的相对变形,使航向载荷分量通过约束装置传递至中央翼盒段,以保证接头的安全。     

应力复合型裂纹焊接接头裂端场及其断裂参量分析

针对含Ⅰ+Ⅱ应力复合型裂纹的焊接接头,应用弹塑性有限元方法分析了其裂端应力场的分布规律。并对不同组配焊接接头的裂纹张开位移(COD)断裂参量及其复合角进行了数值计算,讨论了加载角度和接头强度组配对焊接接头中应力复合型裂纹的断裂行为及其断裂参量的影响机制。研究结果表明,无论何种强度组配,焊接接头裂纹尖端应力场的分布是不对称的。裂端上部发生锐化现象,而裂端下部发生钝化现象。断裂参量COD值的大小受接头组配的影响,因此,不能简单地采用全母材的性能代替接头进行焊接接头的断裂分析。加载角度对焊接接头中复合型裂纹Ⅰ、Ⅱ型主导性存在很大的影响,而接头强度组配对其影响不明显;而裂纹复合角则会受到加载角度及材料组配因素的影响。因此,在进行含应力复合型裂纹的焊接接头的COD断裂参量的计算时,必须考虑这些因素的综合影响作用。     

力学性能不均匀性对焊接接头断裂和疲劳的影响以及焊接接头可靠性的评估

总结近年来我国对力学性能不均匀焊接及钎焊接头断裂和疲劳行为所进行的研究,重点介绍力学不均匀性对夹层含平行于交界面裂纹和夹层含垂直于交界面裂纹的焊接接头断裂行为的影响以及在循环载荷或腐蚀环境下力学不均匀性对其裂纹扩展速率的影响。同时介绍EPRI工程估算方法中有关COD和J积分的修正。     

139.7mm加重钻杆外螺纹接头断裂原因分析

为查明某井139.7 mm加重钻杆外螺纹接头的断裂原因,对断口进行了宏观和微观分析,对材料进行了化学成分分析、力学性能试验和金相分析,并进行了有限元分析等。结果表明:加重钻杆断裂属于腐蚀疲劳断裂;断裂主要原因是加重钻杆接头内径大于标准规定值,降低了加重钻杆外螺纹接头断裂扭矩和抗拉载荷,在疲劳载荷与腐蚀介质作用下,腐蚀疲劳裂纹首先在加重钻杆外螺纹接头危险截面部位螺纹牙底萌生,随后在载荷作用下裂纹不断扩展,进一步降低了接头的强度,最终发生了断裂事故。     

应力脉冲对CCCD-SHPB试验系统测试结果影响的数值分析

3维动态有限元分析结果表明,脉冲上升沿时间、幅值及试件直径对CCCD-SHPB(central cracked circular disk-split Hopkinson pressure bar)动态断裂试验系统的试验结果有较大影响,改变脉冲上升沿时间或脉冲幅值可以得到不同加载速率下材料的动态断裂韧度.进一步计算结果表明,在动态加载的初期阶段,由于试件两边载荷不平衡,导致CCCD-SHPB动态断裂试验系统中存在与试件尺寸相关的特征时间ΔT,且ΔT近似等于应力波在试件中来回往返两次的时间;动态断裂试验时,试件从加载至断裂的时间应大于特征时间ΔT,否则试验结果不可靠.     

EFFECT OF DYNAMIC LOADING ON FRACTURE BEHAVIOR OF WELDED JOINTS OF STRUCTURAL STEEL

To investigate the effect of dynamic loading on fracture behavior of welded joints of structural steel Q23SB and 16Mn in common use and compare the earthquake resistances of the two kinds of materials, dynamic tension and fracture toughness tests are carried out at room temperature. On the basis of the tests, the stress-strain fields near the crack tip of the compact specimens are analyzed by three-dimensional finite element model. The test results and finite element analysis results show that, the fracture toughness of welds and base metal of 16Mn steel increases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is more sensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low under static loading and dynamic loading at room temperature. Compared with the static loading, the fracture toughness of Q235B parent metal under dynamic loading decreases by about four times. Therefore, it can be concluded that compared with 16Mn steel, the earthquake re     

TRANSFERABILITY OF TOUGHNESS RESULT TO FRACTURE PERFORMANCE EVALUATION OF WELDED JOINTS CONSIDERING STABLE CRACK GROWTH

0INTRODUCTIONAttemptsarebeingmadebymany.,.areh..[I~41toaPPlyfracturemechanicstestresultstofractureperformanceevaluationofstmctundcomponents.Thelinkbetweenthefmeturemechanicstestresultsandthefmeturebehaviorofrealisticstructuralcomponentsiscalledfoetransferability.Recently,acProgressivemathalshavebeenp~edtoaddressthetransferability.OneistheJ--TandJ-Qtheori.,L51,wheretheT-stressandQ-p~terhavebeendevelopedtOqUantifythedifferencebetWeenthefull-fieldsolutionforthenearcracktipstressdistribu…     

Dynamic fracture characteristics of highly brittle materials by using Instrumented Charpy Impact Test

In This study we investigate the dynamic fracture characteristics of a tungsten carbide cobalt (WC-6wt%Co) composite material. The dynamic fracture initiation toughness and some of the dynamic fracturing characteristics are evaluated by using the Instrumented Charpy Impact Testing (ICIT) procedure. The dependence of measured time-to-fracture on the tup impact velocity and the dynamic fracture toughness for the WC-6wt%Co composite material are obtained by using ICIT. The effect of the loading rate on fracture initiation toughness is found to be negligible when the time-to-fracture is on the order of 50μsec. At significantly higher rates of loading it is impossible to determine the apparent dynamic fracture initiation toughness because of the influence of the inertia force on fracture loading. It is found that the impact velocities affect the time-to-fracture significantly at lower impact velocities for various engineering materials. It is shown that with the decrease of tup impact velocities the time-to-fracture is increased and the dynamic fracture initiation toughness converges to static fracture toughness.     

Analysis of a composite double cantilever beam with stitched reinforcements under mixed mode loading: Formulation (I)

Several methods for improving the lnterlaminar strength and fracture toughness of composite materials are developed Through-the-thickness stitching is considered one of the most common ways to prevent delamination Stitching significantly increases the Mode I fracture toughness and moderately improves the Mode II fracture toughness An analytical model has been developed for simulating the behavior of stitched double cantilever beam specimen under various loading conditions For z-directional load and moment about the y-axis the numerical solutions are compared with the exact solutions The derived formulation shows good accuracy when the relative error of displacement and rotation between numerical and exact solution were calculated Thus we can use the present model with confidence in analyzing other problems involving stitched beams     

基于局部法定量表征面外拘束效应对转变区间断裂韧度的影响

拘束效应制约了主曲线法表征转变区间的断裂韧度,局部法作为一种细观解理断裂力学方法有望用来解决这个问题。利用两种不同拘束配置的三点弯曲试样,通过交点法标定了国产压力容器用钢Q345R的局部法参量,借助于韧性换算思想将低拘束的试样断裂韧度结果换算成高拘束的结果。通过对比高拘束实测参考温度T 0值,验证了模型的正确性。基于此提出了一种预测不同面外拘束试样参考温度的方法,通过改变厚度的大小,研究了三点弯曲试样厚度对T 0的影响。结果表明,试样厚度越大,韧脆转变温度越高,断裂韧性下降,当厚度大于25.4 mm后会出现一个韧性平台,接近平面应变状态;厚度低于该值会造成严重的拘束缺失,T 0值远大于真实值会造成危险评估,尤其对于低硬化材料,这种现象更为明显。     

预测钛合金超塑成形－扩散连接(SPF/DB)界面层的断裂韧度

提出根据超塑成形－扩散连接(SPF/DB)的工艺技术参数预测扩散连接界面层断裂韧度的计算方法,并对TC4/TA2连接件,开发了相应的界面层断裂韧度的分析和预测软件系统。该计算方法首先在理论分析和试验的基础上,建立扩散连接界面层成长模型,获得扩散连接件界面层厚度的计算公式,确定材料过渡参数m的计算方法;其次对已有的混合型外载的界面断裂准则进行修正,使其适用于扩散连接件界面层断裂时能量释放率曲线的函数模型。计算结果与试验结果吻合良好。分析结果表明：在允许工艺参数范围内,扩散连接件界面断裂韧度随成形温度、成形压力和保压时间的提高而提高。其中,成形压力影响最大,然后依次为保压时间和成形温度。为了提高扩散连接界面层的断裂韧度,必须通过界面层设计来提高其界面裂尖断裂混合度,而上述各工艺技术参数,正与其裂尖断裂混合度的大小密切相关。     

A probabilistic model for the scale effect on fracture toughness of structural ceramics

The fracture toughness of polycrystalline ceramics used to present the scale effect as well as statistical distribution. It is believed that both (scale effect and scatter) must be associated with the heterogeneity of materials. However, no generally accepted theory has been established so far. Using statistical approach, a probabilistic modelling for the fracture toughness which describes the scale effect was attempted in this paper. Weibull distribution of specific fracture energy (SFE) at local area and Griffith criterion are jointly applied to the model. Finally, the fracture toughness scale dependence of ASTM E399 standard specimens was investigated by the newly developed model.