• Advanced Composite Materials
• /
• v.18 no.4
• /
• pp.395-413
• /
• 2009

Impact tests on high-strength membrane materials under biaxial loads were experimentally conducted in order to evaluate influence of biaxial loads on impact fracture of the membrane materials for the inflated applications. Cruciform specimens of the membrane materials were fabricated for applying biaxial loadings during the impact test. A steel ball was shot using a compressed nitrogen gas gun, and struck the membrane specimen. Impact tests on uniaxial strip specimens were also conducted to obtain the effect of specimen configuration and boundary condition on the impact fracture. The results of the measured crack length and the ultra-high speed photographs indicate the impact fracture properties of the membrane fabrics under biaxial loadings. Crack length due to the impact increased with applied tensile load, and the impact damages of the cruciform membrane materials under biaxial loadings were smaller than those of under uniaxial loadings. Impact fracture of the strip specimen was more severe than that of the cruciform specimen due to the difference of boundary conditions.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.12 no.1
• /
• pp.62-69
• /
• 2016

Current guidance considers that uniaxially loaded specimen with a deep crack is used for the determination of the ductile-to-brittle transition temperature. However, reactor pressure vessel is under biaxial loading in real and the existence of deep crack is not probable through periodic in-service-inspection. The elastic stress intensity factor and the elastic-plastic J-integral which were used for crack-tip stress field and fracture mechanics assessment parameters. The difference of the loading condition and crack geometry can significantly influence on these parameters. Thus, a constraint effect caused by differences between standard specimens and a real structure can over/underestimate the fracture toughness, and it affects the results of the structural integrity assessment, consequentially. The present paper investigates the constraint effects by evaluating the master curve $T_0$ reference temperature of PCVN (Pre-cracked Charpy V-Notch) and small scale cruciform specimens which was designed to simulate biaxial loading condition with shallow crack through the fracture toughness tests and 3-dimensional elastic-plastic finite element analyses. Based on the finite element analysis results, the fracture toughness values of a small scale cruciform specimen were estimated, and the geometry-dependent factors of the cruciform specimen considered in the present study were determined. Finally, the transferability of the test results of these specimens was discussed.

• Proceedings of the KSME Conference
• /
• 2000.04a
• /
• pp.200-205
• /
• 2000

Fatigue failure modes of load-carrying cruciform weld joints are dependent on the characteristics of the fatigue crack initiation and propagation from the weld toe or the weld root. In this study, constant amplitude fatigue tests on load-carrying fillet welded specimen carried out, and fatigue strengths were evaluated. Also, an attempt is made to develop a new analytical model with more accuracy to predict the fatigue crack propagation life of fillet welded cruciform joints of SWS 490B steels containing lack of penetration defects. From the result of this study, fatigue crack growth characteristics of load-carrying fillet welded cruciform joints, containing lack of penetration defects are found to be affected by the weld geometry, stress range and microstructures of the weld zone.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.1
• /
• pp.38-44
• /
• 2003

In this study, endurance limit and fatigue behavior of load carrying fillet welded cruciform joints depending on commonly used welding methods such as SMAW, SAW, MIG and FCAW are investigated. In respect of endurance limit SMAW specimen showes highest result, and then MIG, SAW, FCAW in descending order. However, SMAW specimen showes lowest crack growth rate and it followed by MIG, FCAW, SAW. By these results, it is needed to use SMAW or MIG welding methods for welding structures with small welding capacity and SAW or FCAW methods for large welding structures with respect to economic benefits and operation efficiency of welding. It was also shown fatigue crack growth rate was more influenced by the strenght of welding materials than the endurance limit of welding materials.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.6 no.1
• /
• pp.20-26
• /
• 2007

In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

• Structural Engineering and Mechanics
• /
• v.52 no.5
• /
• pp.889-901
• /
• 2014

Very long life fatigue tests were carried out on 16Mn steel base metal and its welded joint by using the ultrasonic fatigue testing technique. Specimen shapes (round and plate) were considered for both the base metal and welded joint. The results show that the specimens present different S-N curve characteristics in the region of $10^5-10^9$ cycles. The round specimens showed continuously decreasing tendency while plate specimens showed a steep decreasing step and an asymptotic horizontal one. The fatigue strength of round specimen was found higher than plate specimen. The fatigue strength of as-welded joint was 45.0% of the base material for butt joint and 40% for cruciform as-welded joint. It was found that fracture can still occur in butt joint beyond $5{\times}10^6$ cycles. The cruciform joint has a fatigue limit in the very long life fatigue regime ($10^7-10^9$ cycles). Fatigue strength of butt as-welded joint was much higher as compared to cruciform as-welded joint. Improvement in fatigue strength of welded joint was found due to UPT. The observation of fracture surface showed crack mainly initiated from welded toe at fusion areas or geometric discontinuity sites at the surface in butt joint and from welded toe in cruciform joint.

• Journal of the Korean Society of Safety
• /
• v.15 no.1
• /
• pp.140-145
• /
• 2000

This paper was composed with fatigue test of the cruciform specimens, as load carrying and non-load carrying type. It also has performed computational analyses for geometric condition of the fillet welding bead. As test results, the effect of stress ratio in the specimen was insignificant. Stress ranges were varied with R=0.1~0.2. The fatigue cracks that were found in the load carrying type specimens and most specimens welded with contact were developed at the end of welds. The fatigue strength of specimen that have fractured in maternal plate was found about ${\Delta}\sigma_c$=63.5MPa. It's about 24% less than that of the non-load carrying type specimens having about ${\Delta}\sigma_c$=83.8MPa. A category of the Fatigue design specifications which provide for cruciform details was defined grade C as a stress of the maternal member. And then, the fatigue strength to be transformed into the maternal stress was found about 78.27 MPa, it tends to be less than that of allowable fatigue strength.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.10
• /
• pp.1549-1557
• /
• 2004

Fatigue life of welded joints is governed by the propagation of multiple collinear surface cracks distributed randomly along weld toe. These cracks propagate under the mechanisms of mutual interaction and coalescence of the adjacent two cracks. To estimate the fatigue life, its influences on the above two mechanisms should be taken into account, which appear through the stress intensity factors disturbed mutually. However, it is difficult to calculate the stress intensity factors of the multiple surface cracks located in vicinity of weld toe due to its geometrical complexity. They are calculated normally by using the Μk-factors, but such Mk-factors are very rare in literature. In this study, the Μ$textsc{k}$-factors were obtained from a parametric study on crack length and depth, for which a finite element method is used. A fatigue test for a cruciform welded Joint was conducted and the fatigue life of the tested specimen was estimated using the present method with the informations obtained from the test, such as the number, size, and locations of the cracks. The estimated and measured fatigue life showed a good agreement.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.120-125
• /
• 2004

Fatigue life of welded joints are governed by the propagation of multiple collinear surface cracks distributed randomly along weld bead. These cracks propagate in mutual interaction and coalescence of them. To estimate the fatigue life, the influences of above two mechanisms on the fatigue life should be taken into account. These two mechanisms appear through the stress intensity factors disturbed mutually. However, it is difficult to calculate the stress intensity factors of multiple surface cracks located in vicinity of weld toe. The stress intensity factors are calculated normally by using the Mk-factors, but such Mk-factors are very rare in literature. In this study, the Mk-factors were obtained from a parametric study on crack length and depth, in which a finite element method is used. A fatigue test for a cruciform welded joint was conducted. The fatigue life of the tested specimen was estimated through present method with the informations obtained from the test, e.g. the number, size and locations of the cracks. The estimated and measured fatigue life showed a good agreement.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1774-1779
• /
• 2005

Most of materials receive force in using, therefore, the characteristics of materials must be considered in system design not to occur deformation or destruction. Mechanical properties about materials can be expressed as responsible level of material itself under the exterior operation. Main mechanical properties is strength, hardness, ductility and stiffness etc. Currently, among major measure facilities to measure such mechanical properties, advanced indentation technique has focused in industrial areas as reason of nondestructive and easy applications for mechanical tensile properties and evaluation of residual stress of materials. This study is to find the optimum experimental condition about residual stress advanced indentation technique for accurate analysis of the welded joint of steel materials through indentation load-depth curve obtained from cruciform specimen experiment. Optimum selection was applied to the welded joint of real steel materials to give non-equi-biaxial stress state and compared with general residual stress analyzing method for verification.