• Structural Engineering and Mechanics
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• 제34권2호
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• pp.143-157
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• 2010

This paper presents theoretical solutions for the three-dimensional (3D) stress field in an infinite isotropic elastic plate containing a through-the-thickness circular hole subjected to far-field in-plane loads by using Kane and Mindlin's assumption. The dangerous position, where the premature fracture or failure of the plate will take place, the expressions of the tangential stress at the surface of the hole and the out-of-plane stress constraint factor are found in a concise, explicit form. Based on the present theoretical solutions, a comprehensive analysis is performed on the deviated degree of the in-plane stresses from the related plane stress solutions, stress concentration and out-of-plane constraint, and the emphasis has been placed on the effects of the plate thickness, Poisson's ratio and the far-field in-plane loads on the stress field. The analytical solution shows that the effects of the plate thickness and Poisson's ratio on the deviation of the 3D in-plane stress components is obvious and could not be ignored, although their effects on distributions of the in-plane stress components are slight, and that the effect of the far-field in-plane loads is just on the contrary of that of the above two. When only the shear stress is loaded at far field, the stress concentration factor reach its peak value about 8.9% higher than that of the plane stress solutions, and the out-of-plane stress constraint factor can reach 1 at the surface of the hole and is the biggest among all cases considered.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1531-1538
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• 2003

This paper compiles solutions of plastic $\eta$ factors and crack tip stress triaxialites for standard and nonstandard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament-to-thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental J estimation than that of the LLD, for all cases considered in the present work. Moreover, the J estimation based on the load-CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing specimen with any thickness. The effects of in-plane and out-of-plane constraint on the crack tip stress triaxiality are also quantified, so that when experimental J value is estimated according to the procedure recommended in this paper, the corresponding crack tip stress triaxiality can be estimated. Moreover, it is found that the out-of-plane constraint effect is related to the in-plane constraint effect.

• 한국압력기기공학회 논문집
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• 제15권1호
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• pp.71-76
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• 2019

Actual stress distributions in the nozzle of a pressure vessel may not be in plane strain condition, implying that the crack-tip constraint condition may be relaxed in the nozzle. In this paper, a methodology for evaluating the fracture toughness of the ASME Code is presented considering the relaxation of the constraint effect in the nozzle of the reactor pressure vessel. The crack-tip constraint effect is quantified by the T-stress. The equation, which represent the relation between the fracture toughness in the lower constraint condition and the plane strain fracture toughness, is derived using the T-stress. This equation is similar to the method for evaluating the fracture toughness of the Master Curve for low constraint conditions. As a result of evaluating the fracture toughness considering the constraint effect in the reactor inlet, outlet and direct injection nozzles using the proposed equation, it was confirmed that the fracture toughness in the nozzles is higher than the plane strain fracture toughness. Applying the proposed evaluation methodology, it is possible to reflect the relaxation of the constraint effect in the nozzles of the reactor pressure vessel, therefore, the safe operation area on the pressure-temperature limit curve can be prevented from being excessively limited.

• 대한기계학회논문집A
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• 제24권12호
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• pp.2963-2971
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• 2000

In order to obtain more realistic fracture resistance curve, research is currently underway to introduce new parameter and to quantify the constraint effect. The objective of this study is to investigate the relationship between the constraint effect of a size(plane size and thickness) and the fracture resistance curve. In this paper fracture toughness tests were performed with various plane size and various thickness of specimens in two materials. The test results showed that the effects of plane size in th4 J-R curve were significant and the curve was risen with an increase in plane size. However, relatively weak influence was observed form the change of the specimen thickness and size. The stress fields near the crack tip of th specimen is close to the HRR field according to increasing the plane size and Q stress appears different value according to material properties and the plane size.

• 대한기계학회논문집
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• 제19권8호
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• pp.1799-1809
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• 1995

The applicability of the field-consistency paradigm, which was originally employed for analysis of locking due to constrained energy having the second power of a strain, is extended to the constrained energy having a quadratic form of strain. For the extension, nearly-incompressible plane strain problem is considered by introducing the concept of reduced minimization. The field-consistent analysis of the plane strain problem leads to a clear and systematic understanding on the relation amongst constraints imposed on element, spurious constraint -free optimal points, and integration order used.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.23-31
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• 2003

This paper introduces a constraint operator for the kinematic calibration of a parallel mechanism. By adopting the concept of a constraint operator, the movement between two poses is constrained. When the constrained movements are satisfied, the active joint displacements are taken and inputted into the kinematic model to compute the theoretical movements. A cost function is derived by the errors between the theoretical movement and the actual movement. The parameters that minimize the cost function are estimated and substituted into the kinematic model for a kinematic calibration. A single constraint plane is employed as a mechanical fixture to constrain the movement, and three digital indicators are used as the sensing devices to determine whether the constrained movement is satisfied. This calibration system represents an effective, low cost and feasible technique for a parallel mechanism. A calibration algorithm is developed with a constraint operator and implemented on a parallel manipulator constructed for a machining center tool.

• 대한기계학회논문집A
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• 제38권12호
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• pp.1441-1446
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• 2014

본 논문에서는 휜 광폭평판의 두께와 폭, 균열길이 그리고 가공경화지수의 변화가 휜 광폭평판의 균열부 구속상태에 미치는 영향을 평가하였다. 이를 위해 5가지의 휜 광폭평판 두께, 3가지의 균열길이, 3가지의 휜 광폭평판 폭 그리고 3가지의 가공경화지수를 고려한 3차원 탄소성 유한요소해석을 수행하였다. Ramberg-Osgood 관계식을 만족하는 비선형 재료로 가정하였으며 균열부 구속상태를 정량화하기 위해서 Q-응력을 이용하였다. 3차원 유한요소해석 결과를 바탕으로 기하학적 형상 및 재료특성에 따른 휜 광폭평판의 Q-응력 변화를 평가하였다. 평가 결과 면외 구속조건에 의한 영향은 면내 구속조건과 밀접한 관계가 있었으며, 면외 구속조건이 면내 구속조건 보다 균열부 구속상태에 더 큰 영향을 미쳤다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.2393-2396
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• 2005

We present a method to detect on-road vehicle using geometric invariant of feature points on side planes of the vehicle. The vehicles are assumed into a set of planes and the invariant from motion information of features on the plane segments the plane from the theory that a geometric invariant value defined by five points on a plane is preserved under a projective transform. Harris corners as a salient image point are used to give motion information with the normalized correlation centered at these points. We define a probabilistic criterion to test the similarity of invariant values between sequential frames. Experimental results using images of real road scenes are presented.

• Journal of Welding and Joining
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• 제10권1호
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• pp.35-42
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• 1992

In this study, the stress concentration phenomenon for the dissimilar joints(ceramic-metal) bonded by thermal treating using a soft-insert metal(copper) was investigated with the aid of FEM(finite element method) under the load condition of uniform tension. The analysis was carried out by the supposing that stress states are plane stress or plane strain and elastic or elastic-plastic. And the Von Mises yield criterion and the incremental theory as plastic flow were adopted in this analysis. As the summarized results obtained, the stress concentration phenomenon was severer as the soft insert metal was thicker, in plane strain than in plane stress and in elastic-plastic state than in elastic state. Furthermore, the inducing mechanism of stress concentration was well expressed by the constraint forces(Fc) generated between the soft and the hard material.

• Steel and Composite Structures
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• 제2권4호
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• pp.237-246
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• 2002

In this paper, the solution of a semi-infinite plane with one circular hole is presented. This solution is induced by repeatedly superposing the solution of an infinite plane with one circular hole and that of a semi-infinite plane without holes to cancel out the stresses arising on both boundaries. This procedure is carried out until the stresses arising on both boundaries converge. This method does not require complicated calculation procedures as does the method using stress functions defined in a bipolar coordinate system. Some numerical results are shown by graphical representations.