• 한국자동차공학회논문집
• /
• 제4권4호
• /
• pp.171-178
• /
• 1996

DCB(pure mode I) and CLS(mixed mode) tests were performed to investigate the effect of fracture mode on the interlaminar fracture of composite laminate. Mode I critical strain energy release rate was found to be $133J/m^2$ from the DCB test and total strain energy release rate decreased from $1, 270J/m^2$ as thickness ratio(tl/t) varied from 0.333 to 0.667 from the crease from the CLS test. Crack length had no effect on the total strain energy release rate and load was almost constant during the crack growth of the specimen which had the specific thickness ratio. Crack initiated when the stress of the strap ply reached constant stress $42kgf/mm^2$ which was found to be independent of the thickness ratio.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.837-840
• /
• 2002

An analysis method for rubber toughened PVC is suggested to evaluate critical dynamic strain energy release rates($G_c$) from the Charpy impact energy measurements. An instrumented Charpy impact tester was used to extract ancillary information concerning fracture parameters in addition to total fracture energies and maximum critical loads. The dynamic stress intensity factor $K_{Id}$ was computed for varying amounts of rubber contents from the obtained maximum critical loads and also toughening effects were investigated as well. The fracture surfaces produced under low velocity impact fur PVC/MBS composites were investigated by SEM. The results show that MBS rubber is very effective reinforcement material for toughening PVC.C.

• 터널과지하공간
• /
• 제4권1호
• /
• pp.55-62
• /
• 1994

The hydraulic fracturing in a field site was performed for the measurement of in-situ stresses. For the estimation of the effect of a preexisting inclined fracture, the test on a preexisting fracture zone was also conducted. From the measurements at three shallow depths, the ratios of max. to min. horizontal stress showed the range of 1.19-1.56 and the K values showed the range of 2.62-3.86. In case of a preexisting fracture with the inclination of 15 degrees, the stresses calculated as upper bound values by considering it. It seemed from this that the inclination less than 15 degrees had small effect on the stress calculation.

• 소성∙가공
• /
• 제19권4호
• /
• pp.217-223
• /
• 2010

The objective of this study is to propose the FE model for mechanical clinched joint using cohesive zone model to analyze its failure behavior under impact loading. Cohesive zone model (CZM) is two-parameter failure criteria approach, which could describe the failure behavior of joint using critical stress and fracture toughness. In this study, the relationship between failure behavior of mechanical clinched joint and fracture parameters is investigated by FE analysis with CZM. Using this relationship, the critical stress and fracture toughness for tensile and shear mode are determined by H-type tensile test and lap shear test, which were made of 5052 aluminum alloy. The fracture parameters were applied to the tophat impact test to evaluate the crashworthiness. Compared penetration depth and energy absorption at the point where 50% of total displacement in result of FE analysis and experiment test for impact test, those has shown similar crashworthiness.

• 한국농공학회지
• /
• 제37권3_4호
• /
• pp.90-98
• /
• 1995

The recycled concrete, average compressive strength of which was 2l0kg/cm$^2$ or higher with slump range of 14~18cm, was prepared by replacing 25% and 50% by weight of coarse aggregate with recycled aggregate from waste concrete. Mix design method for crushed aggregates was used and all specimens were cured by normal moisture curing method. A plasticiser and a fly ash were added to the mix to improve performance of recycled concrete. Flexural strength, stress- strain relationship and fracture toughness were evaluated by comparing with those of normal concretes. Recycled concrete showed, in general, lower flexural strength and fracture toughness, and higher strain under the same stress level. Fly ash in the concrete had an effect of reducing the strength and fracture toughness on both normal and recycled concretes. Since fly ash is known to improve many properties of concrete, while reducing strength properties, decision for using fly ash should be made carefully depending on the intended usage of the recycled concrete.

• Advanced Composite Materials
• /
• 제17권3호
• /
• pp.301-317
• /
• 2008

The energy release rate associated with crack growth in adhesive double cantilever beam (DCB) specimens, including the effect of residual stresses, was formulated using beam theory. Because of the rotation of the asymmetric arms in the adhesive DCB specimens due to temperature change, it is necessary to correct the evaluated fracture toughness of the DCB specimens, specifically in the case of a large temperature change. This study shows that the difference between the true toughness and an apparent toughness due to the consequence of ignoring residual stresses can be calculated for a given specimen geometry and thermo-mechanical properties (e.g. coefficient of thermal expansion). The calculated difference in the energy release rates based on the present correction method is compared with that from FEM in order to verify the present correction method. The residual stress effects on the evaluation of the adhesive fracture toughness are discussed.

• Structural Engineering and Mechanics
• /
• 제52권5호
• /
• pp.957-969
• /
• 2014

Among severe plastic deformation methods, groove pressing is one of the prominent techniques for producing ultra-fine grained sheet materials. This process consists of imposing repetitive severe plastic deformation on the plate or sheet metals through alternate pressing. In the current study, a 2 mm pure Cu sheet has been subjected to repetitive shear deformation up to two passes. Hardness and tensile yield and ultimate stress were obtained after groove pressing. Fracture toughness tests have been performed and compared for three conditions of sheet material namely as received (initial annealed state), after one and two passes of groove pressing. Results of experiments indicate that a decrease in the values of fracture toughness attains as the number of constrained groove pressing (CGP) passes increase.

• 한국안전학회지
• /
• 제18권3호
• /
• pp.46-53
• /
• 2003

For the tensile tests of the F.E.M., microvoids are created by the boundary separation process at the martensite boundary or neighborhood and at inclusions within the fracture. to grow to the ductile dimple fracture. For the case of the M.E.F., microvoids created at the discontinuities of the martensite phase which exists at the grain boundary of the primary ferrite are grown to coalescence with the cleavage cracks induced at the interior of the ferrite, which as a result show the discontinuous brittle fracture behavior. In spite of their similar tensile strengths, the fatigue limit and the notch sensitivity of the M. E.F. is superior to those of the F.E.M., The M.E.F. is much more insensitive to notch than F.E.M. from the stress concentration factor($\alpha$).

• Journal of Welding and Joining
• /
• 제17권2호
• /
• pp.76-83
• /
• 1999

Fracture toughness({TEX}$J_{IC}${/TEX}) on 304 austenitic stainless steel weldments artificially degraded for long period under SCC environments were evaluated to investigate its reliability and environmental characteristics. Electro-chemical polarization tests were previously carried out to evaluate corrosion susceptiblility of weldment, and stress corrosion cracking was tested under various conditions of 3.5wt.% NaCl solution, the temperature of $25^{\circ}$C and $95^{\circ}$C, and oxygen concentration during 3000hours. From the results obtained, it was found that 304 stainless steel weldment was so susceptible under high temperature and high oxygen concentration of 3.5wt.% NaCl solution, and fracture toughness({TEX}$J_{IC}${/TEX}) was also considerably reduced by material degradation.

• 사상체질의학회지
• /
• 제13권3호
• /
• pp.140-144
• /
• 2001

Severe chronic coughing infrequently causes rib fractures and these fractures belong to Stress fracture and these rib fractures are given the term of "cough fractur". Cough fracture usually occurs in one rib and in the middle of the rib between the costochondral junction and the costal angle. The case is a report about a young woman with multiple rib fractures which were caused by severe coughing. The Chest PA and Rib series test were normal but Rib fractures were founded by Bone scan test. Treatment was Herb-medication, rest and restriction of work and symptoms were reduced.