• Journal of Welding and Joining
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• v.31 no.1
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• pp.58-64
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• 2013

The following results were obtained, microstructures and tensile properties in arc brazed joints of DP(dual phase) steel using Cu-5.3wt%Sn insert metal was investigated as function of brazing current. 1) The Fusion Zone was composed of ${\alpha}Fe+{\gamma}Cu$ and Cu23Sn2. The reason for the formation of these solid solutions. Despite, Fe & Cu were impossible to solid solution at room temperature. It's melting & reaction to something of insert metal & Base Metal (DP Steel) by Arc. Brazing Process has faster cooling rate then Cast Process, Supersaturated solid solution at room temperature. 2) The increase Hardness of Fusion Zone was directly proportional to the rise of welding current. Because, ${\alpha}Fe+{\gamma}Cu$ phase (higher hardness than the Cu23Sn2.(104.1Hv < 271.9Hv)) Volume fraction was Growth, due to increasing the amount of base metal melting by High current. 3) The results of tensile shear test by Brazing, All specimens happen to fracture in Fusion Zone. On the other hand, when Brazing Current increasing tend to rise tensile load. but it was very small, about 26-30% of the base metal. 4) The result of fracture analysis, The crack initiate at Triple Point for meet to Upper B.M/Under B.M/Fusion Zone. This Crack propagated to Fusion zone. So ruptured by tensile strength. The Reason to in the fusion zone fracture, Fusion zone by Brazing of hardness (strength) was very lower then the base metal (DP steel). In addition the Fusion Zone's thickness in triple point was thin than the base metal's thickness in triple point.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.5
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• pp.653-659
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• 2010

Friction stir welding results in low distortion and high joint strength compared with other welding procedures, and is able to join all aluminium alloys that are not considered as virtually weldable with classical liquid state techniques. The comparative study on high cycle fatigue properties between A16005-T6 friction stir welds and MIG weld joints have been performed and fracture mechanisms for the fatigue specimens were investigated. Although mechanical properties are lower than the corresponding base material, FSW joints of A16005-T6 become higher at tensile and fatigue strength in comparison with the traditional fusion weld(MIG). The fracture surfaces of FSW and MIG fatigue specimens cleary show different aspects of the fracture morphology. MIG weldments were characterized by voids and cleavage(brittle fracture) but FSW specimens showed the presence of ductile fracture surface.

• 연구논문집
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• s.24
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• pp.119-128
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• 1994

A special steels have been developed for the possible applications of turbine blade in nuclear power plant. The compositions of developed alloy were selected by the reference of imported alloy. The various properties such as tensile property, impact energy, hardness, and microstructures were investigated. All the properties of optimum heat treated materials were satisfied with the present specifications of turbine blade materials in unclear power plant. Furthermore, FATT(Fracture appearance transition temperature), high temperature tensile properties, and transformation temperatures of developed alloy also have been studied.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.231-236
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• 2001

A newly developed Advanced Indentation System (AIS), which is a portable and nondestructive system for evaluating tensile properties, was used to measure mechanical behavior of materials used under high temperature and pressure conditions. This test measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation and fracture. Aging effects of Cr-Mo and Cr-Mo-V steel at high temperature were simulated. Tensile properties including yield strength and tensile strength at various temperature are obtained from the test. For all test materials and conditions, the AIS-derived results were in good agreement with those from conventional standard test method. Examples of the test results ate given and potential applications of the AIS to assess the integrity of aging structures are briefly discussed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.11a
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• pp.87-88
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• 2018

In this study, the tensile properties of single and hybrid fiber reinforced cement composite according to strain rate was evaluated. Experimental results, in the strain rate 10^-6/s, fiber reinforced cement composite showed improved of tensile strength and decrease of strain at peak stress as SSF volume content increased. In the strain rate 101/s, the single and hybrid reinforced cement composite's tensile properties are improved, because of the improved bond strength between the fiber and matrix. And hybrid fiber reinforced cement composite showed high energy absorption capacity, because the SSF prevented the cracking and fracture of the surrounding matrix when during the HSF pull-out.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.57-67
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• 2019

Water-induced strength reduction is one of the most critical causes for rock deformation and failure. Understanding the effects of water on the strength, toughness and deformability of rocks are of a great importance in rock fracture mechanics and design of structures in rock. However, only a few studies have been conducted to understand the effects of water on fracture properties such as fracture toughness, crack propagation velocity, consumed energy, and microstructural damage. Thus, in this study, we focused on the understanding of how microscale damages induced by water saturation affect mesoscale mechanical and fracture properties compared with oven dried specimens along three notch orientations-divider, arrester, and short transverse. The mechanical properties of calcite-cemented sandstone were examined using standard uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests. In addition, fracture properties such as fracture toughness, consumed energy and crack propagation velocity were examined with cracked chevron notched Brazilian disk (CCNBD) tests. Digital Image Correlation (DIC), a non-contact optical measurement technique, was used for both strain and crack propagation velocity measurements along the bedding plane orientations. Finally, environmental scanning electron microscope (ESEM) was employed to investigate the microstructural damages produced in calcite-cemented sandstone specimens before and after CCNBD tests. As results, both mechanical and fracture properties reduced significantly when specimens were saturated. The effects of water on fracture properties (fracture toughness and consumed energy) were predominant in divider specimens when compared with arrester and short transverse specimens. Whereas crack propagation velocity was faster in short transverse and slower in arrester, and intermediate in divider specimens. Based on ESEM data, water in the calcite-cemented sandstone induced microstructural damages (microcracks and voids) and increased the strength disparity between cement/matrix and rock forming mineral grains, which in turn reduced the crack propagation resistance of the rock, leading to lower both consumed energy and fracture toughness ($K_{IC}$).

• Carbon letters
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• v.6 no.1
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• pp.6-14
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• 2005

The study of mechanical properties and fracture behaviour of carbon/carbon composites is significant to its application and development. These are dependent on microstructure and properties of reinforcing fibers and matrix, fiber/matrix interface and porosity/cracks present in the composites. In the present studies high-density carbon/carbon composites have been prepared using PAN and various pitch based carbon fibers as reinforcements and pitch as matrix with repeated densification cycles using high-pressure impregnation and carbonization technique. Scanning electron microscopy has been used to study the fracture behaviour of the highly dense composites and correlated with structure of the composites. The geometry of reinforcement and presence of unfilled voids/cracks was found to influence the path of crack propagation and thereby the strength of composites. The type of stresses (tensile or compressive) accumulated also plays an important role in fracture of composites.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.42-51
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• 1985

The dynamic fracture toughness, fracture characteristics, impact tension and tensile properties of Al-Mg-Si T5 alloy and Al-Zn-Mg T6 alloy respectively welded with filler metal of Alcan 4043 were investigated. The dynamic fracture toughness values were obtained rapidly and simply for the specimen of small size by using instrumented Chirpy impact testing machine. the testing temperatures of the specimen were a range of room temperature and-196.deg. C. The results obtained in this experiment are summarized as follows. With decreasing the testing temperatures, dynamic tensile stress and fracture load were increased, on the other hand the deflection and impact value showed decreasing tendency in order of base metal>HAZ>weld. Changes of total absorbed energy were more influenced by the crack propagation energy than the crack initiation energy. At the low temperatures, the unstable rapid fracture representing the crack propagation appeared for the specimens of Charpy press side notched in Al-Zn-Mg alloy, but it was difficult to obtain the unstable rapid fracture in Al-Mg-Si alloy. Because of the development of plastic zone at the notch root, it was difficult to obtain thevalid $K_{1d}$ value in Al-Mg-Si alloy. Therefore the fatigue cracked specimens were effective in both Al-Mg-Si and Al-Zn-Mg alloys. With decreasing the impact testing temperatures, specimens underwent a transition from dimple-type transgranular fracture to lamella surface-type intergranular fracture because of the precipitate at the grain boundaries, impurities and crystal structure of the precipitates.s.

• Journal of Korea Foundry Society
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• v.11 no.1
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• pp.63-70
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• 1991

Aluminium alloy castings, which can be not only manufactured in larger geometrically complex shapes, but also show good mechanical properties in addition to light weight, have kept their potential use as structures in the field of automotives, industrial machines and aircrafts. The variations of eutectic Si size a great effect on the elongation, impact value, fracture toughness and fatigue crack propagation rate without changes in the tensile strength or yield strength. The cooling curves with the solidification rate between $1.4^{\circ}C\;/min$ and $19.1^{\circ}C\;/min$ were obtained. With the increase of solidification rate, DAS, eutectic Si size and grain size were all decreased, which enhanced the mechanical properties. The tensile strength and yield strength were the most greatly influenced by DAS, and the elongation and impact value by eutectic Si size.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.273-278
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• 1998

In this paper, basic micro-mechanical properties of unidirectional CFRP composite shell such as bonding strength, fiber volume fraction and void fraction are measured and tensile strength test is performed with a fixture. And then fracture surfaces are observed by SEM. In case of basic micro-mechanical properties, bonding strength is reduce with decreasing of radius of each ply in a shell for the effect of residual stress, fiber volume fraction is smaller than plate, and void fraction is vise versa. For these reason, tensile strength of shell is smaller than plate fabricated with same prepreg. For failure mode shell has many splitted part along its length, and it is assumed that this phenomenon is caused by the difference of bonding strength for residual stress.