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基于ZSGH4169合金的蠕变试验数据,采用16参数的θ-映射法模型对蠕变曲线进行分析,获得本构方程参数,并以净截面应力作为参考标准,对不同缺口试样的蠕变行为及应力松弛现象进行了模拟分析。结果表明:θ-映射法模型通过获得的参数能够较为准确地描述ZSGH4169合金的蠕变行为;应力集中程度越高,试样缺口根部的蠕变变形越明显,应力松弛程度越高;应力集中系数较小时,缺口试样的蠕变变形向无缺口试样的趋近;引入应力集中系数(或最大应力)、应力梯度影响因子对传统蠕变模型进行修正,给出了缺口试样蠕变变形计算的一般表达式。 相似文献
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本文提出平封头与筒体连接圆角区的应力集中 系数可以用三个无量纲参量,即λ≡h/dt~(1/2),η≡t/d和ρ≡r/t的函数来表示,并根据有限单元法计算结果给出应力集中系数的近似表达式。 相似文献
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机车轮对压装过程弹塑性模拟 总被引:4,自引:0,他引:4
过盈联接存在应力集中,应力集中对联接的可靠性和配合零件的疲劳寿命有着直接的影响,因此,为了保证联接的可靠性和配合零件的疲劳寿命,在设计与制造中必须尽可能地考虑各种因素的影响。用有限元方法对机车轮对压装过程进行了弹性和弹塑性有限元模拟,有限元分析结果表明,弹塑性模拟分析比弹性模拟更加真实,不但能够模拟车轮与车轴中的应力分布,反映轮毂间的接触边缘应力集中等,而且能够比较准确地计算出轮对的塑性变形及其影响,因此,弹塑性有限元分析对安全性要求很高的机车轮对过盈配合的设计和制造就更有指导意义。 相似文献
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有限域中高精度应力集中系数和应力强度因子表达式 总被引:10,自引:1,他引:9
在近似解析的基础上,采用渐近(极限)修正的方法,推出有限域中3个典型的孔、洞和裂纹模型的应力集中系数和应力强度因子的高精度表达式。 相似文献
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链板零件的疲劳强度是研究整链疲劳可靠性的基础,本文通过内、外链板的成组疲劳试验,得到其R-S-N曲线,并就影响链板疲劳可靠性的理论应力集中系数进行了深入系统地研究。本文的研究结果,可作为滚子链疲劳可靠性设计的重要基础资料。 相似文献
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在桥式起重机金属结构的定期检查中,经常在主梁端部过渡圆弧区域的焊缝位置发现裂纹,故在主梁的轻量化设计中需要考虑这一部位的疲劳特性。提出了一种基于热点应力评定主梁端部过渡圆弧区域疲劳特性的优化设计方法,通过有限元仿真计算获得了相应的热点应力集中系数表达式。以结构质量最小为设计目标,在静强度、静刚度、稳定性等常规约束基础上,加入了主梁端部圆弧区段疲劳强度的约束,建立了箱形主梁结构的优化模型。基于Matlab的比较实验证明,在轻量化优化设计中综合考虑端部疲劳特性,其结果具有更高的可靠性。 相似文献
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基于有限元法的桁架节点搭接接头应力集中分析 总被引:1,自引:0,他引:1
应力集中对桁架节点处疲劳寿命影响显著,焊缝处几何形状不规则,易产生应力集中,可能导致结构破坏。为了研究结构的几何尺寸和焊缝的几何形状对焊缝处应力集中系数的影响,将总应力集中系数分解为焊缝几何应力集中系数和热点应力集中系数的乘积形式。用有限元方法分析焊缝长度、焊缝熔深、弦杆厚度和焊脚尺寸对几何应力集中系数和热点应力集中系数的影响,并拟合经验公式。结果表明:弦杆厚度对应力集中影响不大,焊缝截面形状和焊缝长度对应力集中有一定影响。 相似文献
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Zheng Yang Chang-Boo Kim Chongdu Cho 《International Journal of Mechanical Sciences》2010,52(6):836-846
The elastic stress and strain fields of a finite thickness plate containing a circular hole subjected to out-of-plane bending are systematically investigated using the finite element method. It is found that the stress and strain concentration factors of the finite thickness plate are different except at the notch root of the free surface even if the plate is in elasticity state. The through-thickness distributions of strain components are not linear with the distance from the mid-plane in the stress concentration region. The nonlinearity of these distributions is very severe near the free surface especially in thick plate. The Euler-Bernoulli hypothesis and Kane-Mindlin's plate theory may not be reasonable to be used in the stress concentration region especially near the free surface. The maximum stress and strain do not always occur on the free surface and their locations depend on the moment ratio and the plate thickness. The maximum stress and strain concentration factors occur on the free surface only in thin plates of small moment ratio. The differences between the maximum value and surface value of stress concentration factor increase with the plate thickness and the moment ratio. This relation of strain concentration factor is similar to the one of stress concentration factor. But the difference magnitude of stress concentration factor is larger than that of strain concentration factor in same plate. 相似文献
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Abstract A neural network (NN) based adaptive interaction technique is proposed for controlling highly nonlinear neutralization processes. In this approach, the controller is decomposed into interconnected subsystems and adaptation occurs during the interactions. This approach is adaptive in structure and doesn't use an explicit model of the process in the design. The NN is used to establish the adaptive interaction technique for the development of a nonlinear pH controller, which calculates the necessary change in a manipulated variable to drive the system to the desired value. By applying this adaptive algorithm, the same adaptation as the back‐propagation algorithm is achieved without the need of backward propagating the error throughout a feedback network. This important property makes it possible to adapt the NN controller directly without a process model. This advantage reduces the computational complexity drastically in comparison to the well known back‐propagation algorithm based adaptive NN system and a model based system. The designed model‐free online adaptive controller was implemented to a laboratory scaled pH process in real time by use of a dSPACE 1104 interfacing card. The responses of pH and acid flow rate show good tracking for both the set point and load changes over the entire nonlinear region. 相似文献
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基于支持矢量机的疲劳应力集中系数预测模型研究 总被引:1,自引:1,他引:1
疲劳应力集中系数作为材料疲劳抗力指标的疲劳极限,不仅反映了疲劳应力集中的程度,还反映了材料对缺口的敏感程度,将近年来飞速发展的支持矢量机(Support vector machine,SVM)应用于疲劳应力集中系数的研究。介绍支持矢量机的基本原理,利用LIBSVM,选择高斯型径向基函数(Radial basis function,RBF)作为核函数,建立以材料的抗拉强度、屈服强度、光棒疲劳强度、理论应力集中系数、缺口根部半径、试样尺寸及缺口疲劳极限作为输入值,疲劳应力集中系数为输出值的模型,从而对疲劳应力集中系数进行分析和预测。同时,SVM模型与经验公式Neuber式和Peterson式的计算值进行比较。结果表明,在小样本条件下,应用SVM技术构建的数学模型,模型的拟合相对误差小于7.4%,从而证明该SVM模型的准确性和适用性。 相似文献
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变宽度板承受拉伸和弯曲时的三维应力集中 总被引:1,自引:1,他引:0
根据Hellinger Reissner原理 ,建立了具有一个无外力圆柱面的三维杂交应力元 ,元内假定应力场满足以柱坐标表示的三维平衡方程及无外力圆柱面上外力边界条件 ,当元退化为二维时也满足协调条件。单元位移场与相邻元协调。数值算例表明 ,现在的特殊杂交应力元 ,在相当粗的网格下即能高效地分析变宽度厚 (薄 )板的三维及二维应力集中。 相似文献
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以Euler梁为波导耦合的超声发射换能器与接收换能器输入—输出理论分析 总被引:4,自引:0,他引:4
刘铁让 《振动、测试与诊断》1997,17(3):37-42
应力波因子技术是近几年发展起来的评估复合材料损伤的新技术,本文讨论了该技术应用于梁类构件时超声发射换能器与超声接收换能器输入-输出的理论分析问题。通过引入简化假设首先建立起问题的方程,然后借助于多重积分变换方法获得了发射换能器与接收换能器输入-输出关系的频域显式表达式。以此为基础进一步应用解析方法和快速傅里叶变换(FFT)数值方法对接收换能器的时域输出特征进行了理论分析和数值计算。根据本文的分析与计算,最后得出了一些有益的结论 相似文献
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腐蚀坑应力集中系数影响分析 总被引:1,自引:0,他引:1
利用KH-7700型三维显微镜对经过预腐蚀的6151/T6铝合金材料的腐蚀坑三维形貌进行测量分析,发现可以将腐蚀坑近似为规则的半椭球体。对不同加速腐蚀时间的腐蚀坑测量数据统计分析,得到腐蚀坑的三维尺寸比值一般不超过4,极少达到10。基于ABAQUS6.10有限元软件,对含不同形貌、不同位置腐蚀坑的试验件进行应力集中系数分析发现,不同形貌的腐蚀坑随着b/c的增大,应力集中系数逐渐变小,而a/c增大,应力集中系数逐渐变大;对于同一腐蚀坑,试验件在不同位置引起的应力集中,其影响变化不大,大约在5%以内。 相似文献
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Neuber rule and Arola-Ramulu model are widely used to predict the stress concentration factor of rough specimens. However, the height parameters and effective valley radius used in these two models depend strongly on the resolution of the roughness-measuring instruments and are easily introduce measuring errors. Besides, it is difficult to find a suitable parameter to characterize surface topography to quantitatively describe its effect on stress concentration factor. In order to overcome these disadvantages, profile moments are carried out to characterize surface topography, surface topography is simulated by superposing series of cosine components, the stress concentration factors of different micro cosine-shaped surface topographies are investigated by finite element analysis. In terms of micro cosine-shaped surface topography, an equation using the second profile moment to estimate the stress concentration factor is proposed, predictions for the stress concentration factor using the proposed expression are within 10% error compared with the results of finite element analysis, which are more accurate than other models. Moreover, the proposed equation is applied to the real surface topography machined by turning. Predictions for the stress concentration factor using the proposed expression are within 10% of the maximum stress concentration factors and about 5% of the effective stress concentration factors estimated from the finite element analysis for three levels of turning surface topographies under different simulated scales. The proposed model is feasible in predicting the stress concentration factors of real machined surface topographies. 相似文献
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根据1种修正的余能原理,建立了具有1个无外力圆柱表面的12结点三维杂交应力元,其单元内的应力场满足三维柱坐标平衡方程及无外力圆柱面边界条件;当元退化为二维时,也满足协调条件。数值算例表明用这种特殊杂交应力元能十分有效地分析具有偏心圆孔厚(薄)板的三维及二维应力集中。 相似文献