• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.265-270
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• 2002

In this paper, structural behaviors of anchor systems subjected to shear loads are analyzed by using fracture analysis and experiments. Two dimensional finite element analyses of concrete anchor systems to predict breakout failure of concrete through progressive fracture are carried out by utilizing the so-called embedded crack model. Three dimensional finite element analyses are also carried out to investigate the fracture behavior of anchor systems having different effective lengths, edge distances, spacings between anchors, and direction of loads. Results of analyses are compared with both experimental results and design values of ACI code on anchor, and then applicability of finite element method for predicting fracture behavior of concrete anchor systems is verified.

• 대한기계학회논문집A
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• 제29권4호
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• pp.606-613
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• 2005

Effects of circumferentially local wall thinning on the fracture behavior of pipes were investigated by monotonic four-point bending. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area included an eroded ratio of d/t= 0.2, 0.5, 0.6, and 0.8, and an eroded length of ${\ell}\;=10mm,$ 25mm, and 120mm. Fracture type could be classified into ovalization, local buckling, and crack initiation depending on the eroded length and eroded ratio. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors excepting failure due to cracking. It was possible to predict the crack initiation point by estimating true fracture ductility under multi-axial stress conditions at the center of the thinned area.

• 대한기계학회논문집
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• 제13권1호
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• pp.96-104
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• 1989

본 연구에서는 AE법에 의해 J$_{IC}$를 결정하는 것은 Takahashi등의 방법을 따르되 AE 실험결과를 토대로 이론을 전개하여 재료의 물성 곡선인 J-R곡선의 실험식과 재료 찢어짐 계수를 계산할 수 있는 실험식을 유도하며, 이렇게 구한 실험식을 불안정 파괴 조건에 적용하여 그 타당성을 검토한다.다.

• 대한기계학회논문집
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• 제10권2호
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• pp.198-207
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• 1986

본 연구에서는 Fig.1과 같이 시편 부위에 균일응력분포가 작용하도록 M.Arcan 등에 의해 제시된 비대칭형상의 시편고정물에 층간균열을 가진 시편을 부착한 다음 하중각도를 바꾸어가며 모우드 II뿐 아니라 혼합모우드 및 모우드 I까지도 실험 할 수 있는 실험장치를 사용하여 균열면에서의 섬유방향이 〔0/0〕이고 초기균열길이비가 0.4, 0.5, 0.6인 시편의 모우드I, 혼합모우드 및 모우드II 층간파괴인 성치들을 실험 적으로 구해 혼합모우드 파괴결정조건식들에 적용시켜 보았다. 또한 균열면에서의 섬유방향이 〔0/0〕, 〔0/30〕, 〔0/45〕및 〔0/60〕인 경우의 층간파괴인성치와 이때 의 파괴현상에 대해 관찰하였다.

• 대한기계학회논문집A
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• 제31권2호
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• pp.166-173
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• 2007

Fatigue fracture behavior of a hybrid bolted joint was evaluated in comparison to the case of static fracture. Two kinds of specimens were fabricated for the mechanical tests; a hybrid bolted joint specimen for the shear test and a hybrid joint part specimen applied in the real tilting car body for the bending test. Characteristic fracture behaviors of those specimens under cyclic toads were obviously different from the case under static loads. For the hybrid bolted joint specimen, static shear loading caused the fracture of the bolt body itself in a pure shear mode, whereas cyclic shear loading brought about the fracture at the site of local tensile stress concentration. For the hybrid joint part specimen, static bend loading caused the shear deformation and fracture in the honeycomb core region, while cyclic bend loading did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.784-789
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• 2001

In order to investigate the fracture behaviors(penetration modes) and the resistance to penetration during ballistic impact of cold-rolled Al 5052 H34 alloy laminates, anodized Al 5052 H34 alloy laminates, and Al 5052 H34 alloy after cold-rolling, ballistic testing was conducted. In general, superior armor material is brittle materials which have a high hardness. Ballistic resistance of these materials was measured by protection ballistic limit(V50), a statical velocity with 50% probability for incomplete penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, are observed respectfully, resulting from V50 test and Projectile Through Plate(PTP) test at velocities greater than V50. PTP tests were conducted with 0$^{\circ}$obliquity at room temperature using 5.56mm ball projectile. V50 tests with 0$^{\circ}$obliquity at room temperature were also conducted with projectiles that were able to achieve near or complete penetration during PTP tests. Surface Hardness, resistance to penetration, and penetration modes of Al 5052 H34 alloy laminates compared to those of cold-rolled Al 5052 H34 alloy laminates and anodized Al 5052 H34 alloy laminates anodized Al 5052 H34 alloy after cold-rolling.

• 한국정밀공학회지
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• 제20권3호
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• pp.178-186
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• 2003

In order to investigate the fracture behaviors (penetration modes) and the resistance to penetration during ballistic impact of Al 5052-H34 alloy laminates, cold-rolled Al 5052-H34 alloy laminates, anodized Al 5052-H34 alloy laminates, and anodized Al 5052-H34 alloy after cold-rolling, a ballistic testing was conducted. In general, superior armor materials are brittle materials which have a high hardness. Ballistic resistance of these materials was measured by a protection ballistic limit (V$_{50}$), a statistical velocity with 50% probability fur incompletete penetration. Fracture begaviors and ballistic tolerance, described by penetration modes, ate observed from the results from the results of V$_{50}$ test and Projectile Through Plates (PTP) test at velocities greater than V$_{50}$, respectively. PTP tests were conducted with 0$_{\circ}$obliquity at room temperature using 5.56mm ball projectile. V$_{50}$ tests with 0$_{\circ}$obliquity at room temperature were concucted with projectiles that could achieve neat or complete penetration during PTP tests. Surface hardness, resistance to penetration, and penetration modes of Al 5052-H34 alloy laminates are compared to those of cold-rolled Al 5052-H34 alloy laminates and anodized Al 5052-H34 alloy laminates and anodized Al 5052-H34 cold-rolled alloy.

• 대한금속재료학회지
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• 제48권7호
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• pp.683-689
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• 2010

In this study, FeAl based intermetallic matrix composites reinforced with in-situ synthesized TiC particles were fabricated by an in-situ liquid mixing process. The microstructures, mechanical properties and fracture behaviors of the in-situ liquid mixing processed composite were investigated and compared with the vacuum suction casting processed composite. The results showed that the in-situ formed TiC particles exhibited fine and uniform dispersion in the liquid mixing processed composite, while significant grain boundary clustering and coarsening of TiC particles were obtained by the vacuum suction process. It was also shown in both types of composites that the hardness and bending strength were increased with the increase of the TiC volume fractions. Through the study of fractography in the bending test, it was considered that the TiC particles prohibited brittle intergranular fracture of FeAl intermetallic matrix by crack deflections. Because of the uniformly distributed fine TiC particles, the bending strength of the liquid mixing processed composite was superior to that of the casting processed composite.

• 한국해양공학회지
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• 제25권2호
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• pp.134-144
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• 2011

In this paper, the global study trends for material behaviors are investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after reviewing all of the papers published at the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized, explicitly presenting the material properties. Although some studies have attempted to employ new plasticity and fracture models, it is obvious that most still employed an ideal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency of material strain hardening at various levels of temperature, but did not show strain rate hardening at intermediate or high strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. The main goal of this paper is to provide the theoretical background for strain and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for the dynamic hardening constitutive equations of power from Cowper-Symonds and Johnson-Cook.

• 대한기계학회논문집A
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• 제34권1호
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• pp.55-60
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• 2010

틸팅형 고속열차의 차체에 적용되는 하니컴 복합재 조인트 구조물의 경우 운행중 외팔보형 굽힘하중을 받게된다. 하이브리드 복합재 조인트 구조물에 대한 굽힘시험평가를 수행하기 위해 실제 틸팅열차 차체 구조물에서 조인트부를 절단 채취하여 시험편으로 제작하였다. 굽힘시험결과 시험편의 파괴거동은 정적하중과 피로하중하에서 확연히 달라짐을 보였다. 정적굽힘하중 하에서는 하니컴 코어 영역에서 전단변형과 파괴가 발생하였으며, 피로굽힘하중 하에서는 복합재 표피층과 하니컴 코어층 사이에서 계면분리가 발생하거나, 또는 금속재 언더프레임과의 용접부에서 파괴가 발생하였다. 이러한 파괴거동은 다른 산업분야에서 사용되는 유사한 구조의 하니컴 복합재 조인트 구조물에서도 발생할 수 있기 때문에, 본 실험 결과를 하니컴 복합재 조인트 구조물의 설계변수를 개선하기 위해 이용될 수 있다.