• Journal of Ocean Engineering and Technology
• /
• v.11 no.3
• /
• pp.20-28
• /
• 1997

The fatigue crack propagation properties and fatigue life of two kinds of Al body panel for automobile were examined experimentally by using the plate specimen and the single spot welding specimen. The fatigue limit of spot welding specimens was lower than that of a plate specimen. The fatigue limit was similar in two kinds of spot welding specimen. The shape and size of crack propagation were observed and measured on beach mark of fracture surface. The crack propagation of surface crack specimen showed almost same tendency to that of a thick plate as almost semi-elliptical. In spot welding specimen, the fatigue crack occurred in inside surface of nugget area was almost semi-elliptical. The crack growth rate can be explained using equation of stress intensity factors.

• Journal of the Korea Concrete Institute
• /
• v.16 no.3 s.81
• /
• pp.375-382
• /
• 2004

The compressive strength of concrete is used as the most basic and important material Property when reinforced concrete structures are designed. It has become a problem to use this value, however, because the control specimen sizes and shapes are different from every country. In this study, the effect of specimen sizes and shapes on compressive strength of concrete specimens was experimentally investigated based on fracture mechanics. Experiments for the Mode I failure was carried out by using cylinder, cube, and prism specimens. The test results are curve fitted using least square method(LSM) to obtain the new parameters for the modified size effect law(MSEL). The analysis results show that the effect of specimen sizes and shapes on ultimate strength is apparent. In addition, correlations between compressive strengths with size, shape, and casting direction of the specimen are investigated. For cubes and prisms the effect of placing direction on the compressive strength was investigated.

• Journal of Welding and Joining
• /
• v.1 no.2
• /
• pp.53-60
• /
• 1983

COD test based on fracture mechanics concept was used in this study to evaluate the fracture toughness quantitatively. Effects of specimen sizes on critical COD value for ABS EH 36 steel and its submerged arc weldments, and the variation of critical COD value depending on metallurgical/mechanical heterogeneities caused by weld thermal cycles were investigated. Experiment was performed by using specimens made from base metal and submerged arc weldments according to BS 5762. Obtained results are summarized as follows; 1) Critical COD value for base metal decreases with increasing thickness of specimen. On hand, as the reduction ratio of critical COD decreases with increasing specimen thickness, critical COD value becomes constant above a thickness of specimen. 2) Critical COD value for weldment decreases with increasing thickness of specimen and was also affected by metallurgical states of base metal. 3) Size effects for weldment was greater at the hardened region. 4) Critical COD value was affected by microstructural change due to weld thermal cycles in weldments; that is, accicular ferrite formation is favorable for increasing of COD value.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.132-137
• /
• 2001

Miniaturized specimen technology is useful to characterize the mechanical behavior using a minimum volume of material, because it is almost impossible to sample the conventional specimen for the fracture toughness test without damage to equipment. Test material was 1Cr-1Mo-0.25V steel which was widely used for turbine rotor material. Two kinds of miniaturized impact specimens were prepared, i.e., miniaturized specimen with side groove and without side groove. The correlation between ductile brittle transition temperature(DBTT) of full size impact specimen and that of miniaturized impact specimen was made. The characteristics of miniaturized impact specimens technique as well as fracture stress were discussed. Finally, we concluded that the characteristics of fracture stress change on aging time were similar to that of DBTT.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.47 no.4
• /
• pp.43-52
• /
• 2005

It is known in some literatures that the B value is not equal to unity in saturated soil when effective stress is given, in which the B Value is the ratio of measured excess pore water pressure and isometric loading pressure. In this study the B value was measured on various effective stresses and on various incremental loading stresses in various grain size of specimens with saturated sand. The test results showed that the B value was affected largely by grain size of sand in specimen and the amount of effective stress. There was the semi-logarithmic relationship between B value and effective stress, and also there was the linear relationship between the gradient of the former semi-logarithmic relationship and grain size of specimen.

• Journal of the Korean Ceramic Society
• /
• v.47 no.2
• /
• pp.157-162
• /
• 2010

Effect of starting SiC particle size on nitridation rate and flexural strength of $Si_3N_4$-bonded-SiC (SNBSC) ceramics was investigated by using SiC particles of different size (${\sim}200\;{\mu}m$, ${\sim}100\;{\mu}m$ and ${\sim}45\;{\mu}m$). The specimen prepared from smaller SiC particles resulted in higher nitridation rate after nitridation at $1450^{\circ}C$, owing to the lower packing density in green body. The flexural strength showed maxima after 1-h nitridation for all specimens and then decreased with prolonged nitridation because of local densification-induced pore coarsening. The specimen prepared from smaller SiC particles showed better flexural strength because of smaller pore size and partly higher nitridation rate in the specimen. A maximal flexural strength of 29 MPa was obtained in the specimen with a density of $2.04\;g{\cdot}cm^3$, which was prepared from $45\;{\mu}m$-SiC particles.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.12
• /
• pp.1047-1054
• /
• 2008

In this paper, the molecular dynamics (MD) simulations are performed with single-crystal copper blocks under simple shear and simple tension to investigate the effect of size and crystal orientation. There are many variances to give influences such as deformation path, temperature, specimen size and crystal orientation. Among them, the crystal orientation has a primary influence on the volume averaged stress. The numerical results show that the volume averaged shear stress decreases as the specimen size increases and as the crystal orientation changes from single to octal. Furthermore, the Schmid factor and yield stress for crystal orientation are evaluated by using the MD simulation on the standard triangle of stereographic projection.

• Applied Microscopy
• /
• v.32 no.4
• /
• pp.311-317
• /
• 2002

There is great requirement on the TEM specimen preparation method with particle size selectivity as a prerequisite for the quantitative structure analysis on the materials such as gibbsite powder, which generally forms a large agglomerate and shows a variation of transition process depending on their sizes. In this experiment, we made an attempt to give a methodology for the TEM specimen preparation of powder with the size selectivity. After mixing 1 wt% gibbsite powder with ethanol solvent, gibbsite suspension was prepared by application of ball-milling and ultrasonification with addition of 0.25 vol% dispersion agent, Darvan C, which was diluted into distilled water by the ratio 1:19. Appling the static sedimentation method to gibbsite suspension after estimation of the sedimentation time by the measurement of accumulative concentration variation, we acquired TEM specimens with well-dispersed and size selected gibbsite particles in nm scale. Overall picture of each sample was taken by SEM and morphology of each dispersed particle was imaged by TEM. Raw and processed gibbsite powders were also examined by XRD to investigate whether they were suffered from phase change during the process or not.

• Korean Journal of Materials Research
• /
• v.3 no.2
• /
• pp.197-204
• /
• 1993

Abstract The effects of the hole size and the specimen width on the fracture behavior of several fabric composite plates are experimentally investigated in tension. Tests are performed on plain woven glass/ epoxy, plain woven carbon/epoxy and satin woven glass/polyester specimens with a circular hole. It is shown in this paper that the characteristic length according to the point stress criterion depends on the hole size and the specimen width. An excellent agreement is found between the experimental results and the analytical predictions of the modified failure criterion. The notched strength increase with an increase in the damage ratio, which is explained by a stress relaxation due to the formation of damage zone. When the unstable fracture occurred, the critical crack length equivalent for the damage zone is about twice the characteristic length. The critical energy release rate $G_c$ is independent of hole size for the same specimen width. The variation of $G_c$ according to the material system, fiber volume fraction and specimen width relates to the notch sensitivity factor. $G_c$ increases with a decrease in the notch sensitivity factor, which can be explained by a stress relaxation due to the increase of damage zone.

• Journal of the Korean Ceramic Society
• /
• v.36 no.7
• /
• pp.718-724
• /
• 1999

Densification and grain growth behavior of bimodal size distributed alumina powder mixtures were investigated as a function of amount of coarse alumina powder. The specimens which contained coarse alumina powder for 60to 80wt% showed the highest green density. The amount of shrinkage of sintered specimen lineraly decreased with the increase of coarse alumina powder up to the content that showed the highest green density and then further addition of coarse alumina powder led to drastic decrease of shrinkage of specimen. Especially crack-like void were concurrently revealed in the sintered body with addition of coarse alumina powder above 60wt% When the sintering temperature increased up to 1650$^{\circ}C$ the amount of shrinkage of specimen linearly decreased and the grain growth were also retarded with increase of coarse lauminia powder.