Fracture and Strength of Solids VI

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Authors: Chyan Bin Hwu
Abstract: The crack problems are important not only in macromechanics but also in micromechanics. Because of its importance a lot of analytical, numerical and experimental studies have been published in journals and books. Among them, the study of Green’s function attracts many researchers’ attention because analytically it may provide solutions for arbitrary loading through superposition and numerically it can be employed as the fundamental solutions for boundary element method and as the kernel functions of integral equations to consider crack interaction problems. Although a lot of Green’s functions have been presented in the literature, due to mathematical infeasibility most of them are restricted to two-dimensional problems and very few of them consider possible coupled stretching-bending analysis which may occur for general unsymmetric composite laminates subjected inplane and/or out-of-plane forces and moments. In this paper we consider an infinite composite laminate containing a traction-free crack subjected to concentrated forces and moments at an arbitrary point of the laminate. By employing Stroh-like formalism for the coupled stretching-bending analysis, recently the Green’s functions for the infinite laminates (without holes) were obtained in closed-form. Based upon the non-hole Green’s functions, through the use of analytical continuation method the Green’s functions for cracks are now obtained in explicit closed-form and are valid for the full fields. By proper differentiation, the associated stress intensity factors are also solved explicitly.
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Authors: You Tang Li, Chang Feng Yan
Abstract: The fracture designs of metallic matrix crack for bi-materials were studied. The stress field and displacement field of plane matrix crack was setup at first. Then the finite element method is used to analyses the stress singularity of matrix cracks between different materials. The solutions of stress singularity of a cracked bi-materials beam under uniform tension, and the three-point bending of bi-materials specimen were computed. The result lays a theoretic and applied foundation for the practical engineering application of metallic matrix crack for bi-materials.
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Authors: Shu Cai Li, Wei Shen Zhu, Yu Yong Jiao, H. Jian
Abstract: By using the real-time CT (computerized tomography) unit with specially developed water-injection loading apparatus, several failure tests of single-crack concrete specimens with interstitial water pressures under triaxial compression were conducted. The complete failure process: the closure, the initiation of new damage area, the secondary closure, as well as the crack propagation of the specimens were simulated. The CT images at each stage, the CT numbers and the comparison among different sections in the specimens were obtained. Based on the observed results, the role of compressive pressure in damage and propagation of hydrous crack can be intuitively revealed, and the characteristics of damage-evolution of cracks in brittle material can be better understood at meso-level.
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Authors: Sung Choong Woo, Dae Joon Kim, Nak Sam Choi
Abstract: Acoustic emission (AE) characteristics have been studied for single-edge-notched monolithic thin aluminum (Al) plates and glass fiber/Al hybrid laminates. Traveling microscope was used for observing the plastic deformation and damage zone around the initial notch tip. Frequency characteristics of AE signals processed by fast Fourier transform (FFT) from monolithic Al could be classified into two different types. Type I signal had a relatively low frequency band of 96~260kHz, while Type II signal had broad band frequencies of 192~408kHz. In case of glass fiber/Al hybrid laminates, AE signals with high amplitude (>80dB) and long duration (>2msec) were additionally confirmed on FFT frequency analysis, which corresponded to macro-crack propagation and/or delamination between aluminum layer and glass fiber layer. Also, distributions of the first and the second peaks in frequency spectrum were related with local fracture behaviors of the hybrid laminates. AE source location determined by signal arrival time showed the extent of fracture zones. On the basis of the above AE analysis, characteristic features of fracture processes of single-edge-notched glass fiber/aluminum laminates were elucidated according to different fiber orientations.
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Authors: Yun Jae Kim, Chang Gyun Oh
Abstract: This paper proposes slip line fields for bending of unequally grooved specimens that has a sharp crack in one side and a sharp V-notch in the other side. Depending on the back angle, two slip line fields are proposed, from which the limit moment and crack tip stress fields are obtained as a function of the back angle. Excellent agreements between slip line field solutions with those from detailed finite element limit analysis based on non-hardening plasticity provide confidence in the proposed slip line fields. Based on these results, possibility of designing a new toughness testing specimen with varying crack tip constraint is discussed.
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Authors: Zheng Yang, Wanlin Guo, Quan Liang Liu
Abstract: Stress and strain singularity at crack-tip is the characteristic of Linear Elastic Fracture Mechanics (LEFM). However, the stress, strain and strain energy at crack-tip may be infinite promoting conflicts with linear elastic hypothesis. It is indicated that the geometrical nonlinear near the crack-tip should not be neglected for linear elastic materials. In fact, the crack-tip blunts under high stress and strain, and the singularity vanishes due to the deformation of crack surface when loading. The stress at crack-tip may still be very high even though the singularity vanishes. The low bound of maximum crack-tip stress is the modulus of elastic in plane stress state, while in plain strain state, it is greater than the modulus of elastic, and will increase with the Poisson’s ratio.
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Authors: Zhi Jie Zhang, Qun-Liang Han, Shao Wei Liu, Ying Ming Li
Abstract: Since the broken phenomenon is always appeared in the roof of mine roadway, it largely affects the roadway’s roof stability. With Material Mechanics theory, the authors expound bolt tail subjected to no center load action and roof bolt broken mechanism while roadway is supported with bolts. By theoretical analysis and Lab test, the paper puts forward a kind of new type bolts which may prevent bolt tails from being broken, bolt construction structure’s pattern, and bolt made technology. It is illustrated that the reasonable grading relationship between bolt body’s iameter and bolt tail’s screw diameter. At same time, the authors compare disturbed values of the thick tail metal bolt and common bolt under the load action. It is verified that roof bolt broken problem may be solved with new type’s thick tail bolt. Therefore, the new type bolts have a wide application in the future.
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Authors: M. Ridha, V.P.W. Shim, L.M. Yang
Abstract: A fracture criterion for rigid polyurethane foam is developed based on idealization of constituent cells by elongated tetrakaidecahedra. The ability of the proposed geometrical model to mimic the fracture characteristics of actual rigid polyurethane foam is examined and a fracture criterion derived analytically. In tandem, the fracture properties of an actual rigid polyurethane foam are obtained from mechanical tests. The fracture criterion based on the model exhibits correspondence with the behavior of actual foam. Consequently, this model constitutes a suitable basis for further investigation into the mechanical properties of actual polymeric foams.
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Authors: T. Dirgantara, I.S. Putra, A.A. Sucipto, A. Jusuf
Abstract: The presence of cracks or similar imperfections can considerably reduce the buckling load of a shell structure. In this paper, buckling analysis of cylindrical shells with a longitudinal crack is presented. Numerical buckling analyses of cylindrical shells were performed using FEM, and verified by experiment. The numerical analyses and experiments were conducted for several crack lengths and radius of curvature, and two different boundary conditions were applied, i.e. simply support and clamp in all sides. The results show the effect of the presence of crack to the critical buckling load of the shells. There are good agreements between experimental and numerical results.
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Authors: I.S. Putra, T. Dirgantara, Firmansyah, M. Mora
Abstract: In this paper, buckling analysis of cylindrical shells with a circumferential crack is presented. The analyses were performed both numerically using FEM and experimentally. The numerical analyses and experiments were conducted for several crack lengths and radius of curvature, and two different boundary conditions were applied, i.e. simply support and clamp in all sides. The results show the effect of the presence of crack to the critical buckling load of the shells. There are good agreements between experimental and numerical results.
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