• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.1-8
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• 2015

In this paper, computational evaluation method for fatigue crack growth rate(FCGR) based on material viscoplastic-damage model is proposed. Viscoplastic-damage model expressing material constitutive behavior of 7% nickel steel is introduced and is implemented into commercial finite element analysis(FEA) code, ABAQUS, as a user defined material subroutine(UMAT) for application in the FEA environments. Verification of developed UMAT and material parameters of material model are carried out by uniaxial tensile test simulations of 7% nickel steel. Moreover, jump-in-cycles procedure and rearrangement of critical damage are employed and also implemented to the ABAQUS UMAT for fatigue damage analysis. Typical FCGR test results such as relationship between crack length and number of cycles and relationship between da/dN and ${\Delta}K$ could be obtained from FCGR test simulation using developed UMAT and these results are compared with experimental results in order to verify of proposed computational method.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.1
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• pp.52-60
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• 2015

In the present study, an evaluation method for progressive failure of composite laminates has been proposed based on Puck's failure criterion and damage mechanics. The initial failure (or initiation of crack/delamination) has been assessed using Puck's failure criterion, and the progressive failure (or growth of crack/delamination) has been evaluated using fiber- and matrix-dependent damage variables. Based on Puck's failure criterion-damage mechanics coupling theories, the ABAQUS user-defined subroutine UMAT has been developed in order to analyze the progressive failure of glass/carbon fiber-reinforced composite laminates efficiently. In addition, the developed subroutine has been applied to progressive failure problem of industrial composite laminates, and the analysis results has been compared to experimental results which have been already reported in publications. It was confirmed that the simulation results were coincided well with the reported composite failure results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.491-496
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• 2013

Finite element simulations of tensile tests were performed to determine the equivalent stress - equivalent plastic strain curves, critical equivalent stresses, and critical equivalent plastic strains. Then, the curves were used as inputs to finite element simulations of fracture toughness tests to determine the plane strain fracture toughness. The critical COD was taken as the COD when the equivalent plastic strain at the crack tip reached a critical value, and it was used as a crack growth criterion. The relationship between the critical COD and the critical equivalent plastic strain or the reduction of area was found. The relationship between the plane strain fracture toughness and the product of the critical equivalent stress and the critical equivalent plastic strain was also found.

• Steel and Composite Structures
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• v.48 no.1
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• pp.103-111
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• 2023

The caving property of top coal is a key factor to the success of top coal caving mining. The influence law of cyclic loading and unloading of hydraulic support on top coal caving is of great significance to improve the recovery rate of top coal. The similar simulation methods were used to study the dynamic evolution of the top coal cracks under the multi-cycle action of the support, and the parameters of top coal cracks were analyzed quantitatively in this paper. The results show that the top coal cracks can be divided into horizontal cracks and vertical cracks under the cyclic loading and unloading of the support. With the increase of the times of the support cycles loading and unloading, the load on the support decreases, the fractal dimension of the cracks increases, the number and total length of the top coal cracks increases, and the top coal caving is getting better. With the increase of the times of multi-cycle loading and unloading, the fractal dimension, total crack length and crack rate of top coal show a trend of rapid increase first and then increase slowly. Both the total length of the top coal cracks and the crack rate basically show linear growth with the change of the fractal dimension. The top coal caving can be well improved and the coal resource recovery rate increased through the multi-cycle loading and unloading.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1435-1439
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• 2002

This paper presents a form of the cohesive surface separation potential, which can produce potential curves by varying a single dimensionless parameter. Results show that a partial modification of Xu and Needleman's (1994) cohesive surface separation potential makes it possible to present the other potential corves as a special case as long as the normal separation is concerned. The proposed potential may describe interfacial debonding-crack initiation and growth-character of materials and, through numerical simulation, provide an insight for the effect of different cohesive surface separation potentials on the interfacial debonding.

• Geomechanics and Engineering
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• v.20 no.6
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• pp.485-495
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• 2020

Based on the movement characteristics of overlying strata with gangue backfilling, the compression test of gangue is designed. The deformation characterristics of gangue is obtained based on the different Talbot index. The deformation has a logarithmic growth trend, including sharp deformation stage, linear deformation stage, rheological stage, and the resistance to deformation changes in different stages. The more advantageous Talbot gradation index is obtained to control the surface subsidence. On the basis of similarity simulation test with gangue backfilling, the characteristics of roof failure and the evolution of the supporting force are analyzed. In the early stage of gangue backfilling, beam structure damage directly occurs at the roof, and the layer is separated from the overlying rock. As the working face advances, the crack arch of the basic roof is generated, and the separation layer is closed. Due to the supporting effect of filling gangue, the stress concentration in gangue backfilling stope is relatively mild. Based on the equivalent mining height model of gangue backfilling stope, the relationship between full ratio and mining height is obtained. It is necessary to ensure that the gradation of filling gangue meets the Talbot distribution of n=0.5, and the full ratio meets the protection grade requirements of surface buildings.

• Journal of the Semiconductor & Display Technology
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• v.14 no.1
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• pp.19-25
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• 2015

Strengthened glass is widely used in the display industry for the smart phone and the tablet PC's, the market of which shows steady growth. The strengthened glass is prone to the fracture due to the machined surface defects such as crack and notch. The surface defects are caused mostly by the vibrations of the laser cutter. In this study, the vibrations of the laser cutter were investigated through the frequency response experiment and the computer simulation. The main reasons of the structural vibrations were analyzed, and further the design alterations were deduced and applied to the machine to check the effects of those alterations and to eventually improve the structural stability. The result shows that simple design modifications without major structural change can substantially suppress the vibrations, and improve the quality of the machined surface.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.2
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• pp.101-108
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• 2007

This paper presents an efficient meshless method for analyzing cracked piezoelectric structures subjected to mechanical and electrical loading. The method employs an element free Galerkin (EFG) formulation and an enriched basic function as well as special shape functions that contain discontinuous derivatives. Based on the moving least squares (MLS) interpolation approach, The EFG method is one of the promising methods for dealing with problems involving progressive crack growth. Since the method is meshless and no element connectivity data are needed, the burdensome remeshing procedure required in the conventional finite element method (FEM) is avoided. The numerical results show that the proposed method yields an accurate near-tip stress field in an infinite piezoelectric plate containing an interior hole. Another example is to study a ceramic multilayer actuator. The proposed model was found to be accurate in the simulation of stress and electric field concentrations due to the abrupt end of an internal electrode.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.32-39
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• 2011

The present investigation was performed on the die compaction and sintering behavior of Fe micro-nano mixed powder with a mixed binder for powder injection molding. Warm die compaction of the feedstock for simulation of the static injection molding process was conducted using a cylindrical mold of 10 mm diameter at $100^{\circ}C$ under 4MPa. The die compaction of the micro-nanopowder feedstock underwent a uniform molding behavior showing a homogeneous distribution of nanopowders among the micropowders without porosity and distortion. After debinding, the powder compact maintained a uniform structure without crack and distortion, leading to a high green density of 64.2% corresponding to the initial powder loading of 65%. The sintering experiment showed that the micro-nanopowder compact underwent a near full and isotropic densification process during sintering. It was observed that the nanopowders effectively suppressed the growth of micropowder grains during densification process. Conclusively, the use of nanopowder for PIM feedstock might provide a new concept for processing a full density PIM parts with fine microstructure.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.361-370
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• 2017

Through the use of finite element analysis and acoustic emission techniques we have evaluated the interfacial failure of a carbon fiber reinforced polymer (CFRP) repair patch on a notched aluminum substrate. The repair of cracks is a very common and widely used practice in the aeronautics field to extend the life of cracked sheet metal panels. The process consists of adhesively bonding a patch that encompasses the notched site to provide additional strength, thereby increasing life and avoiding costly replacements. The mechanical strength of the bonded joint relies mainly on the bonding of the adhesive to the plate and patch stiffness. Stress concentrations at crack tips promote disbonding of the composite patch from the substrate, consequently reducing the bonded area, which makes this a critical aspect of repair effectiveness. In this paper we examine patch disbonding by calculating the influence of notch tip stress on disbond area and verify computational results with acoustic emission (AE) measurements obtained from specimens subjected to uniaxial tension. The FE results showed that disbonding first occurs between the patch and the substrate close to free edge of the patch followed by failure around the tip of the notch, both highest stress regions. Experimental results revealed that cement adhesion at the aluminum interface was the limiting factor in patch performance. The patch did not appear to strengthen the aluminum substrate when measured by stress-strain due to early stage disbonding. Analysis of the AE signals provided insight to the disbond locations and progression at the metal-adhesive interface. Crack growth from the notch in the aluminum was not observed until the stress reached a critical level, an instant before final fracture, which was unaffected by the patch due to early stage disbonding. The FE model was further utilized to study the effects of patch fiber orientation and increased adhesive strength. The model revealed that the effectiveness of patch repairs is strongly dependent upon the combined interactions of adhesive bond strength and fiber orientation.