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Study on Thickness Effect of Three-Point-Bend Specimen 三点弯曲试件的厚度效应研究
M. Kikuchi, Takehito Ishihara
The thickness effect of a three-point-bend (3PB) specimen on dimple fracture behavior is studied experimentally and numerically. At first, fracture toughness tests were conducted using 3PB specimens of different thicknesses. Fracture toughness values and R-curves are obtained, and the thickness effect is discussed. Using scanning electron microscopy (SEM), dimple fracture surfaces are observed precisely. It is found that the thickness effect appears clearly in the void growth process. Finite element (FEM) analyses are conducted based on these experimental data. Using Gurson’s constitutive equation, the nucleation and growth of voids during the dimple fracture process are simulated. The distribution patterns of stress triaxiality and the crack growth process are obtained. The results show a good agreement with experimental ones qualitatively. The effects of specimen thickness on R-curves are explained well on the basis of these numerical simulations.
研究了三点弯曲(3PB)试样厚度对韧窝断裂行为的影响。首先,采用不同厚度的3PB试样进行断裂韧性试验。得到了断裂韧性值和r曲线,并讨论了厚度效应。利用扫描电子显微镜(SEM)对韧窝断口表面进行了精确观察。结果表明,在孔洞生长过程中,厚度效应明显。基于这些实验数据进行了有限元分析。利用Gurson本构方程,模拟了韧窝断裂过程中空洞的形核和扩展。得到了应力三轴性分布规律和裂纹扩展过程。定性分析结果与实验结果吻合较好。在此基础上,较好地解释了试样厚度对r曲线的影响。
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引用次数: 1
Finite Deformation Analysis Using Natural Strain 利用自然应变的有限变形分析
Y. Kato
The effectiveness of the Natural Strain theory for describing a large deformation is mentioned in this paper. The Natural Strain is obtained by integrating infinitesimal strain increment on an identical line element over the whole process of the deformation path. Consequently, the shearing strain becomes pure angular strain, which is obtained by removing the rigid body rotation from the rotating angle of a line element. Since the expression of the Natural Strain is different from the strain expression of ordinary rate type, the additive low of strain on an identical line element can be satisfied. In this paper, the finite deformation analyses of a pure elastic body concerning the three different types of deformation paths are discussed on the combined deformation of uni-axial tension and simple shear, and the Natural Strain proposed in this paper is compared with other strain expressions and the rationality of this strain expression is confirmed.
本文讨论了自然应变理论在描述大变形时的有效性。自然应变是通过在变形路径的整个过程中对同一线元上的无穷小应变增量进行积分得到的。因此,剪切应变变为纯角应变,该角应变是通过从线素的旋转角度去除刚体旋转而得到的。由于自然应变的表达式与普通速率型的应变表达式不同,同一线元上的应变可以满足加性低。本文讨论了纯弹性体在单轴拉伸和单纯剪切组合变形下三种不同变形路径下的有限变形分析,并将本文提出的自然应变与其他应变表达式进行了比较,证实了该应变表达式的合理性。
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引用次数: 3
Experimental Study on Applicability of Passive Electric Potential CT Method for Identification of Three-Dimensional Surface Crack 被动电位CT法识别三维表面裂纹适用性的实验研究
D. Shiozawa, S. Kubo, T. Sakagami
In this paper, we examine the applicability of the passive electric potential CT (computed tomography) method to the quantitative identification of three-dimensional cracks in structures. In this method, a piezoelectric film is glued on the surface of structures. The electric potential values on the piezoelectric film change due to the strain distribution on the surface of the structures, when the structures are subjected to an external load. The strain distribution induces an electric potential distribution on the piezoelectric film. Then, this method does not require electric current application, and passively observed electric potential values on piezoelectric film can be used for crack identification. The electric potential distribution on piezoelectric film was investigated numerically and experimentally. It was found that the electric potential distribution shows a characteristic change corresponding to the shape of the surface crack. An inverse method based on the least residual method was applied to crack identification from the electric potential distribution. In this inverse method, the square sum of residuals is evaluated between the measured electric potential distributions and those computed from the electric potential distribution of the piezoelectric film. Three-dimensional surface cracks were identified from the measured electric potential distribution. It was found that the location and size of the crack can be quantitatively estimated using a two-dimensional distribution of electric potential.
在本文中,我们研究了被动电位CT(计算机断层扫描)方法在结构三维裂缝定量识别中的适用性。在这种方法中,压电薄膜被粘在结构的表面。当结构受到外部载荷作用时,由于结构表面的应变分布,使得压电膜上的电势值发生变化。应变分布导致压电薄膜上的电位分布。其次,该方法不需要施加电流,可以通过被动观察压电膜上的电势值进行裂纹识别。对压电薄膜上的电势分布进行了数值和实验研究。结果表明,电势分布随表面裂纹形状的变化呈特征性变化。将基于最小残差法的逆方法应用于电势分布的裂纹识别。该方法利用实测电势分布与压电薄膜电势分布计算结果的差值平方和进行计算。根据测得的电势分布,确定了三维表面裂纹。研究发现,利用二维电势分布可以定量估计裂纹的位置和大小。
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引用次数: 9
Effect of Temperature on the Microscopic Appearance of the Fracture Surface of Alloy 690TT under SSRT Testing 温度对690TT合金断口显微形貌的影响
Yuzuru Ito, Zhanpeng Lu, H. Miura, T. Yonezawa, T. Shoji
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引用次数: 3
Analytical Modeling of Stress-Strain Behaviors under Static and Cyclic Conditions from a Microstructural Viewpoint 静力和循环条件下应力-应变行为的微观分析模型
Tomonori Watanabe
In order to understand nonlinear behaviors of stress-strain responses of metallic materials under static and cyclic conditions from the viewpoint of their microscopic structures, we theoretically investigate an analytical model by applying some mathematical techniques such as the soliton theory and the theory of nonlinear systems which develop greatly in recent years. The analytical model is based on the typical atomic chain model which includes topological defects and consists of the thermal effect, the interactions of atoms, the friction from the environment and the external force. In addition, the analytical model is developed from the typical atomic chain model by including the effects which can relate with work hardening and internal friction. In the static case, we show that inelastic behavior is displayed by the analytical model. In the cyclic case, by using the analytical model, we obtain the nonlinear behavior of the hysteresis loop which qualitatively corresponds to well-known experimental data better than that of the typical model.
为了从微观结构的角度理解金属材料在静循环条件下的应力应变响应的非线性行为,本文运用近年来发展迅速的数学技术,如孤子理论和非线性系统理论,从理论上研究了一种解析模型。解析模型是基于典型的包含拓扑缺陷的原子链模型,由热效应、原子间相互作用、环境摩擦和外力等因素组成。此外,在典型的原子链模型的基础上,考虑了加工硬化和内摩擦的影响,建立了解析模型。在静态情况下,我们证明了解析模型显示了非弹性行为。在循环情况下,用解析模型得到的滞回线的非线性特性比典型模型的特性更能定性地符合已知的实验数据。
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引用次数: 0
Thermo-Mechanical and Low Cycle Fatigues of Single Crystal Ni-Base Superalloys; Importance of Microstructure for Life Prediction 单晶ni基高温合金的热-机械疲劳和低周疲劳微观结构对寿命预测的重要性
M. Sakaguchi, M. Okazaki
Behavior of thermo-mechanical fatigue (TMF) of a single crystal Ni-base superalloy, CMSX-4, was studied, compared with that of isothermal low-cycle fatigue (LCF). Strain-controlled TMF and LCF tests of CMSX-4 were carried out under various test conditions, where the experimental variables were strain rates, strain ratio, temperature range, and strain/temperature phase angle. At first it was shown experimentally that the TMF and LCF failures took places, associated with some noteworthy characteristics which were rarely seen in the traditional polycrystalline heat resistant alloys. They could not be explained reasonably, based on the historical approaches. A new micromechanics model was proposed to predict the TMF and LCF lives, applying the Eshelby’s theory and the Mori-Tanaka’s averaging approximation. The model presented in this paper enabled us to successfully estimate not only the unique characteristics in the TMF and LCF failures but also the effect of γ’ geometry on the LCF lives.
研究了单晶镍基高温合金CMSX-4的热机械疲劳(TMF)行为,并与等温低周疲劳(LCF)进行比较。在应变率、应变比、温度范围、应变/温度相角等试验条件下,对CMSX-4进行应变控制TMF和LCF试验。首先,实验证明了TMF和LCF的失效,并伴有一些传统多晶耐热合金中很少出现的值得注意的特性。根据历史的方法,它们无法得到合理的解释。应用Eshelby理论和Mori-Tanaka平均近似,提出了一种新的预测TMF和LCF寿命的细观力学模型。本文提出的模型使我们不仅能够成功地估计TMF和LCF失效的独特特征,而且还可以估计γ′几何形状对LCF寿命的影响。
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引用次数: 13
Mechanical Evaluation of the Skeletal Structure and Tissue of the Woodpecker and Its Shock Absorbing System 啄木鸟骨骼结构和组织及其减震系统的力学评价
J. Oda, J. Sakamoto, K. Sakano
A woodpecker strikes its beak toward a tree repeatedly. But, the damage of brain or the brain concussion doesn’t occur by this action. Human cannot strike strongly the head without the damage of a brain. Therefore, it is predicted that the brain of a woodpecker is protected from the shock by some methods and that the woodpecker has the original mechanism to absorb a shock. In this study, the endoskeltal structure, especially head part structure of woodpecker is dissected and the impact-proof system is analyzed by FEM and model experiment. From the results, it is obvious that the woodpecker has the original impact-proof system as the unique states of hyoid bone, skull, tissue and brain. Moreover it is considered that woodpecker has the advanced impact-proof system relating with not only the head part but also with the whole body.
啄木鸟不停地用嘴啄树。但是,大脑的损伤或脑震荡并不是由这个动作引起的。人类不可能在不损伤大脑的情况下猛烈撞击头部。因此,可以预测,啄木鸟的大脑有一定的保护措施,并且具有原始的吸收冲击的机制。本文对啄木鸟的内骨骼结构,特别是头部结构进行了解剖,并采用有限元法和模型实验对其抗冲击系统进行了分析。从结果可以看出,啄木鸟的舌骨、颅骨、组织和大脑具有原始的抗冲击系统的独特状态。而且认为啄木鸟不仅头部而且全身都有先进的抗冲击系统。
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引用次数: 52
Effects of Frequency on the Crack-Healing Behavior of Si3N4/SiC Composite under Cyclic Stress 频率对循环应力下Si3N4/SiC复合材料裂纹愈合行为的影响
Koji Takahashi, Yuuta Mizobe, K. Ando, S. Saito
Si3N4/SiC ceramics were hot-pressed to investigate the effect of stress frequency on the crack-healing behavior under cyclic stress. The specimens having pre-crack of 100µ m were subjected to crack-healing under constant or cyclic bending stresses of 300MPa at temperatures between 800 and 1200°C. The resultant bending strength of the crack-healed specimen was investigated. At a healing temperature of 900°C, the pre-cracks had been completely healed both under constant stress and cyclic stress of 0.5Hz. However, the pre-cracks had not completely healed under a cyclic stress of 5 and 10Hz. Thus, the stress frequency affects crack-healing behaviors at 900°C. On the other hand, when the healing temperature was higher than 1000°C, the pre-cracks were healed completely under both constant stress and cyclic stress up to 10Hz. The effects of stress frequency were dependent on the healing temperature. The reasons for this were discussed from the viewpoint of competitive mechanism of fatigue crack growth and crack-healing.
采用热压法制备Si3N4/SiC陶瓷,研究应力频率对循环应力下裂纹愈合行为的影响。预裂纹为100µm的试件在800 ~ 1200℃的温度下,在300MPa的恒定或循环弯曲应力下进行裂纹修复。研究了裂纹愈合试件的综合抗弯强度。在900℃的修复温度下,在恒应力和0.5Hz的循环应力下,预裂纹均完全愈合。然而,在5和10Hz的循环应力下,预裂缝没有完全愈合。因此,应力频率影响900℃时的裂纹愈合行为。另一方面,当愈合温度高于1000℃时,在恒应力和高达10Hz的循环应力下,预裂纹都能完全愈合。应力频率的影响与愈合温度有关。从疲劳裂纹扩展和裂纹愈合的竞争机制的角度探讨了造成这一现象的原因。
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引用次数: 4
Molecular Dynamics Simulations of Shape-Memory Behavior Based on Martensite Transformation and Shear Deformation 基于马氏体相变和剪切变形的形状记忆行为分子动力学模拟
T. Uehara, Takato Tamai, N. Ohno
Molecular dynamics simulations of the shape-memory effect are carried out to investigate the atomistic behavior during deformation and shape-recovery processes. The embedded-atom-method potential function and parameters for Ni-Al alloy are applied. The initial configurations of atoms are set on the lattice points of the martensite structure, in which the distribution of the variant orientation is limited to the two-dimensional direction for simplicity. When the shear load is imposed toward the x direction, parallel to the variant interface, the deformation of the variants occurs, and finally, all variants settle into the uniform orientation. The deformed state is maintained after the load is released, and the original shape is recovered through heating and cooling processes because of phase transformation to bcc and martensite. In the loading process, the stress-strain curve exhibits a zigzag shape consisting of repeated stress increase and abrupt release. The interval of the stress peaks is revealed to be smaller as the model size becomes larger. Deformation observed in variant layers seems to occur at the same time at every points in the layer for a small model. However, the simulation with a large model indicates a nucleation and propagation behavior in each layer.
对形状记忆效应进行了分子动力学模拟,研究了变形和形状恢复过程中的原子行为。采用嵌入原子法对镍铝合金进行势函数和参数分析。原子的初始构型设置在马氏体结构的晶格点上,为简单起见,其中变取向的分布仅限于二维方向。当剪切荷载沿x方向平行于变异体界面施加时,变异体发生变形,最终所有变异体都趋于均匀方向。释放载荷后,合金保持变形状态,由于相变为bcc和马氏体,通过加热和冷却过程恢复到原来的形状。在加载过程中,应力-应变曲线呈反复应力增加和突然释放的锯齿形。应力峰值的间隔随着模型尺寸的增大而减小。对于一个小模型,在不同层中观测到的变形似乎在层中的每一点同时发生。然而,在大模型下的模拟表明,每一层都有形核和扩展行为。
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引用次数: 10
Characterization of Fracture Process in Ceramic-Metal Functionally Graded Material under Three-Point-Bending 陶瓷-金属功能梯度材料三点弯曲断裂过程表征
K. Tohgo, A. Hadano
This paper deals with fracture process of a ceramic-metal functionally graded material (FGM) under three-point-bending. The used material was fabricated by powder metallurgy using partially stabilized zirconia (PSZ) and stainless steel (SUS 304), and has a functionally graded surface layer (FGM layer) on a SUS 304 substrate. In order to investigate the fracture process of the FGM, three-point-bending tests of rectangular specimens and numerical analysis are carried out. During the three-point-bending tests, crack initiation and unstable crack growth occur in the FGM layer, and the crack is arrested at the interface between the FGM layer and the substrate. Then, the crack branches and both crack tips grow stably along the interface with increasing deformation. After some amount of crack growth, both crack tips are arrested, and a new crack is initiated and grows into the SUS 304 substrate ahead of the initial cracking of the FGM layer. The finite element analysis taking account of gradation of material composition and plasticity of SUS 304 phase is carried out for each stage of fracture process. Based on the numerical results of the stress intensity factor, plastic zone and stress distribution, the fracture behavior of the FGM is discussed in detail.
研究了陶瓷-金属功能梯度材料在三点弯曲作用下的断裂过程。所使用的材料是用部分稳定的氧化锆(PSZ)和不锈钢(sus304)通过粉末冶金制成的,并在sus304衬底上具有功能梯度的表面层(FGM层)。为了研究FGM的断裂过程,进行了矩形试件的三点弯曲试验和数值分析。在三点弯曲试验中,FGM层发生裂纹萌生和不稳定裂纹扩展,裂纹止裂于FGM层与基体的界面处。随着变形的增大,裂纹分支和两个裂纹尖端沿界面稳定生长。经过一定程度的裂纹扩展后,两个裂纹尖端都被阻止,并且在FGM层发生初始裂纹之前产生一个新的裂纹并扩展到SUS 304基体中。对断裂过程的各个阶段进行了考虑材料成分梯度和sus304相塑性的有限元分析。基于应力强度因子、塑性区和应力分布的数值计算结果,详细讨论了FGM的断裂行为。
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引用次数: 10
期刊
Jsme International Journal Series A-solid Mechanics and Material Engineering
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