• Steel and Composite Structures
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• v.15 no.2
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• pp.203-220
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• 2013

The study of the tensile strength of composite materials is far more complex than analysis of the properties of elasticity and plasticity. Indeed, during mechanical loading, micro-cracks in the matrix, the fibers break, debonding of the interfaces are created. The failure process of composites is of great diversity and cannot be described if even we know: the strength criterion of each individual component, the state of stress and strain in the material, the propagation phenomena cracks in the structure and nature of the interface between the matrix and the reinforcement. This information is only partially known and the obtained by the analysis of a stress limit beyond which there is destruction of the material is almost impossible. To partially process the issue, a solution lies in a mesoscopic approach of seeking a law to locate the ultimate strength of the material for a plane stress state. Tests on rectangular plates in bending PEEK/APC2 and T300/914 three were made and this in order to validate our approach, the calculation has been implemented in a nonlinear finite element code (Castem 2000), in order to make comparison with the numerical results. The results show good agreement between numerical simulation and the two materials; however, it would be interesting to consider other phenomena in the criterion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.139-146
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• 2002

This paper provides validations of the reference stress based J and $C^{*}$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^{*}$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^{*}$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.front.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.310-315
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• 2001

This paper provides validations of the reference stress based J and $C^*$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^*$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^*$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2313-2318
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• 2000

The method of photoelasticity allows one to obtain principal stress differences and principal stress directions in a photoelastic model. In the classical approach, the photoelastic parameters are measured manually point by point. This is time consuming and requires skill in the identification and measurement of photoelastic data. Fringe phase shifting method has been recently developed and widely used to measure and analyze fringe data in photo-mechanics. This paper presents the test results of photoelastic fringe phase shifting method for the stress analysis of a curved beam plate. The technique used here requires four phase stepped photoelastic images obtained from a circular polariscope by rotating the analyzer at 0˚, 45˚, 90˚ and 135˚. Experimental results are compared with those of ANSYS and calculated by the simple beam theory. Good agreement among the results can be observed.

• Steel and Composite Structures
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• v.27 no.1
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• pp.13-25
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• 2018

The main objective of this study is to develop a dual approach for geometrically nonlinear finite element analysis of plane truss structures. The geometric nonlinearity is considered using the Total Lagrangian formulation. The nonlinear solution is obtained by introducing and minimizing an objective function subjected to displacement-type constraints. The proposed method can fully trace the whole equilibrium path of geometrically nonlinear plane truss structures not only before the limit point but also after it. No stiffness matrix is used in the main approach and the solution is acquired only based on the direct classical stress-strain formulations. As a result, produced errors caused by linearization and approximation of the main equilibrium equation will be eliminated. The suggested algorithm can predict both pre- and post-buckling behavior of the steel plane truss structures as well as any arbitrary point of equilibrium path. In addition, an equilibrium path with multiple limit points and snap-back phenomenon can be followed in this approach. To demonstrate the accuracy, efficiency and robustness of the proposed procedure, numerical results of the suggested approach are compared with theoretical solution, modified arc-length method, and those of reported in the literature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1127-1134
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• 2002

The present paper provides an engineering J estimation equation for surface cracked plates under combined bending and tension. The proposed equation is based on the reference stress approach, and the most relevant normalising loads to define the reference stress for accurate J estimations are given for surface cracked plates under combined bending and tension. Comparisons with J results from extensive 3-D FE analyses, covering a wide range of crack geometry, plate geometry and loading combination, show overall good agreement not only at the deepest point but also at arbitrary points along the crack front. for pure tension, agreement between the estimated J and the FE results is excellent, even at the surface point. On the other hand, for pure bending and combined bending and tension, the estimated J values become less accurate for locations close to the surface point. Thus the results in this paper will be useful to assess short-term fracture or low cycle fatigue of surface defects in plates under combined bending and tension.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.89-94
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• 2008

This paper deals with the method of self-equilibrium stress mode analysis of cable dome structures. From the point of view of analysis, cable dome structure is a kind of unstable truss structure which is stabilized by means of introduction of prestressing. The prestress must be introduced according to a specific proportion among different structural member and it is determined by an analysis called self-equilibrium stress mode analysis. The mathematical equation involved in the self-equilibrium stress mode analysis is a system of linear equations which can be solved numerically by adopting the concept of Moore-Penrose generalized inverse. The calculation of the generalized inverse is carried out by rank factorization method. This method involves a parameter called epsilon which plays a critical role in self-equilibrium stress mode analysis. It is thus of interest to investigate the range of epsilon which produces consistent solution during the analysis of self-equilibrium stress mode.

• Structural Engineering and Mechanics
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• v.18 no.1
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• pp.113-124
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• 2004

The information on local stress acting in a bridge is required in many occasions such as fatigue assessment. The analysis by beam elements cannot yield this class of information adequately, while the finite element modeling of an entire long-span bridge by shell elements is impractical. In the present study, the hybrid modeling is tried out: only part of a bridge in which the point of interest is located is discretized by shell elements and the remaining part is modeled by beam elements. By solving a simple box girder problem, the effectiveness of this approach is discussed. This technique is then applied to the Rama IX Bridge for local stress evaluation. The numerical results compare very well with the results of a full-scale static loading test. The present research thus offers a practical yet accurate technique for the stress analysis of a long-span cable-stayed bridge.

• Korea-Australia Rheology Journal
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• v.20 no.4
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• pp.253-260
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• 2008

A method based on transient shear flow dynamics of red cell aggregates was developed to investigate reversible re-aggregation processes with decreasing shear flow. In the microchannel-flow aggregometry, the aggregated red blood cells that are subjected to continuously decreasing shear stress in microchannel flow were measured with the use of a laser-scattering technique. Both the laser-backscattered intensity and pressure were simultaneously measured with respect to time, resulting in shear stress ranging from $0{\sim}35\;Pa$ for a time period of less than 30 seconds. The time dependent recording of the backscattered light intensity (syllectogram) yielded an upward convex curve with a peak point, which reflected the transition threshold of aggregation in the RBC suspensions. Critical-time and critical-shear stress corresponding to the peak point were examined by varying the initial pressure-differential and the micro channel depth, and these results showed good potential for being used as new aggregation indices. In the present study, these newly proposed indices were also validated by differentiating the effect of fibrinogen on RBC aggregation and then these indices were compared to the conventional indices that were measured by a rotational aggregometer.

• Journal of Theoretical and Applied Mechanics
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• v.2 no.1
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• pp.31-50
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• 1996

In this paper, a finite element analysis based on the local approach concept to fracture in the continuum damage mechanics is performed to analyze ductile fracture in two dimensional quasi-static state. First an isotropic damage model based on the generalized concept of effective stress is proposed for structural materials in the context of large deformation. In this model, the stiffness degradation is taken as a measure of damage and so, the fracture phenomenon can be explained as the critical deterioration of stiffness at a material point. The modified Riks' continuation technique is used to solve incremental iterative equations. Crack propagation is achieved by removing critically damaged elements. The mesh size sensitivity analysis and the simulation of the well known shearing mode failure in plane strain state are carried out to verify the present formulation. As numerical examples, an edge cracked plate and the specimen with a circular hole under plane stress are taken. Load-displacement curves and successively fractured shapes are shown. From the results, it can be concluded that the proposed model based on the local approach concept in the continuum damage mechanics may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.