• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2002.02a
• /
• pp.245-252
• /
• 2002

Ultrasonic machining technology has been developed over recent years for the manufacture of cost-effective and quality-assured precision parts for several industrial application such as optics, semiconductors, aerospace, and automobile. Ultrasonic machining process is an efficient and economical means of precision machining of ceramic materials. The process is non-thermal, non-chemical and non-electric md hardly creates changes to the mechanical properties of the brittle materials machined. This paper describes the characteristics of the micro-hole of $Al_2O_3$ by ultrasonic machining with tungsten carbide tool. The effects of various parameters of ultrasonic machining, including abrasives, machining force and pressure, on the material removal rate, hole quality, and tool wear presented and discussed. The ultrasonic Machining of micro-holes in ceramics has been under taken and the machining mechanism in the ultrasonic machining of ceramics based on the fracture-mechanics concept has been analyzed.

• Structural Engineering and Mechanics
• /
• v.75 no.5
• /
• pp.559-569
• /
• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.13 no.5
• /
• pp.50-56
• /
• 2005

Aluminum member absorbs energy by stable plastic deformation under axial loading. While CFRP(Carbon Fiber Reinforced Plastics) member absorbs energy by unstable brittle failure but its specific strength and stiffness is higher than those of aluminum member. In this study, for complement of detects and synergy effect by combination with the advantages of each member, the axial collapse tests were performed for aluminum CFRP members which are composed of aluminum members wrapped with CFRP outside aluminum circular members. Based on the respective collapse characteristics of aluminum and CFRP members, crushing behavior and energy absorption characteristics were analyzed for aluminum CRRP members which have different CFRP fiber orientation angle and thickness Test results showed that aluminum CFRP members supplemented the unstable brittle failure of CFRP members due to ductile nature of inner aluminum members. It turned out that the CFRP fiber orientation angle and thickness influence energy absorption capability together with the collapse mode of the members.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1997.04a
• /
• pp.182-190
• /
• 1997

A new method to prevent reinforced concrete columns from brittle failure. The method is called transversely reinforcing method in which only the critical regions are confined in steel tube. The steel tubes can change the failure mode of the latter columns from the shear to the flexure. The steel tubes also increase the compressive strength, shear strength and deformation capacity of the infilled concrete. The following conclusions are reached on bases of the study on the seismic performance of the high-strength RC rectangualr short columns confined in steel tube with shear span tho depth ratio of 2.0 The brittle shear failure of high-strength reinforced concrete short columns with large amount of longitudinal bars, which cannot prevented by using the maximum amount of welded hoops, can be prevented by using the steel tube which confines all the maximum amount of welded hoops, can be prevented by using the steel tube which confines all the concrete inclusive of cover concrete. High-strength RC short columns confined in rectangular steel tube provided excellent enhancement of seismic performance but, found that plastic buckling of the steel tube in the hinge regions tended to occur when the columns were subjected to large cyclic lateral displacements. In order to prevent the plastic buckling when the columns lies on large on cyclic lateral displacements, the steel ribs were used for columns. Tests have established that the columns provide excellent enhancement of seismic performance of inadequately confined columns.

• Proceedings of the Safety Management and Science Conference
• /
• 2009.11a
• /
• pp.471-481
• /
• 2009

This study is deal with the high frequency induction hardening (HF at $850^{\circ}C$, 120kHz & 50kW condition) SM45C steel. (1) The HF specimen which was tempered at $150^{\circ}C$, did not appear any tempering effect. A brittle fracture occurred at rounded area of the tensile specimen. AE amplitude distribution showed between 45~60dB. (2) The HF specimen which was tempered at $300^{\circ}C$, slip and fracture occurred at the hole area of the tensile specimen. As it passes the yield point, the AE energy increased intermittently and AE amplitude distribution showed between 70~85dB. In addition, after the maximum tensile load, it showed high amplitude and energy distribution. The AE amplitude showed between 45~70dB. (3) The HF specimen which was tempered at $450^{\circ}C$, a brittle fracture occurred as if it is torn in the direction of $45^{\circ}$ on parallel area over the both sides of the tensile specimen, which led to several peak to be appeared in AE energy. It was found that the AE amplitude was relatively low and the AE energy was high.

• Transactions of Materials Processing
• /
• v.12 no.6
• /
• pp.588-596
• /
• 2003

The relationships between evolution of microstructure and mechanical properties of porous Al-3Si-2Mg-2Cu alloy after the foaming and various heat treating were investigated. The foamed alloy having various densities were manufactured by powder compact foaming and heat treated. Then compression test was performed with deformation rate of 0.5/s. The ultimate compression strength was not changed after solution heat treatment but the flow curve after ultimate strength showed very smooth and uniform plateau region. This change of flow curve means that the deformation mechanism is altered from brittle fracture to ductile deformation and the energy absorption property of Al foam is dramatically improved. The improvement of energy absorption without any detriment of mechanical properties is due to that the very brittle precipitation like Al-Cu and Al-Mg was uniformly dissolved in Al matrix after solution heat treatment. And various mechanical properties of Al alloy porous material were improved by 40% with aging of $200^{\circ}C$ and 50min. These improvements are ascribe to the various fine precipitates like $\Omega$ and $\theta$'.

• Journal of Welding and Joining
• /
• v.3 no.1
• /
• pp.11-21
• /
• 1985

The line heating is a thermoplastic working technique which is used in bending work of steel plate and in correcting the distortion of welded structure. This method is considerably effective when the water-cooling is followed. In this study, an investigation was accomplished to find the effects on the change of material properties when the line heating was applied on the high tensile steel plate of 50kg/mm^2$ grade. Some steel plates were heated to various temperatures and then cooled with water or in the air. In this study, the author measured the angular distortion continuously during line heating to find out the relation between the bending efficiency and heating or water-cooling temperature. Furthermore, its material properties were examined by the V-notch Charpy impact test, the microscope observation and the Vickers hardness test. As results, the followings were clarified. (1) The amount of angular distortion increases as the heating temperature or the water-cooling temperature rises. (2) When the steel plate is heated between 700.deg. C and 900.deg. C, and then is water-cooled over 700.deg. C, some brittle structure is observed. But if the temperature of water-cooling is below 700.deg. C, no brittle one is found. (3) When the steel plate is heated over 800.deg. C and is cooled in the air, there is no unfavrable effect.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1161-1162
• /
• 2006

In order to overcome the recrystallization embrittlement and irradiation embrittlement of Mo, which are major problems for its fusion applications, internally nitrided Mo alloys were prepared by a novel multi-step internal nitriding. Neutron irradiation was performed in the Japan Material Testing Reactor (JMTR). After irradiation, nitrided Mo alloys exhibited $\iota$ ower ductile-brittle transition temperature than irradiated TZM. These results suggested that multi-step internal nitriding was effective to the improvement in the embrittlement by irradiation. Transmission electron microscope observation revealed that TiN particles precipitated by nitriding acted as a sink for irradiation-induced defects.

• Journal of the Society of Naval Architects of Korea
• /
• v.30 no.4
• /
• pp.102-111
• /
• 1993

One of the most important design procedures for large sized structures is the evaluation of fracture strength against fatigue and brittle fractures threatening to occur in their steel members. In this paper, the safety assessment based upon the knowledge about the fracturing characteristics of such ship structures was discussed, which can be estimated from such phenomena as fatigue crack propagation and brittle fractures, as obtained by employing fracture mechanics at the basic design stage. Model tests with a partial structure specimen of full size was carried out to authenticate a question as to whether or not the fracturing characteristics of such sophisticated structures could be estimated with precision from ordinary scale specimen tests, It was shown that the behviour of fatigue crack growth of large sized structures in this study could be predicted from the results of ordinary scale specimen test.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05a
• /
• pp.111-114
• /
• 2005

While the existing reinforced concrete flat plate(RC flat plate) has a lot of advantages including reduced building height, it has some weak points such as many steel bars and the brittle rupture by punching shear. Compared with the RC flat plate, the post-tensioned flat plate (PT flat plate) has not only the same merits, but it also makes longer span possible and induces slab-column connections to be failed with the ductile behavior rather than with the brittle behavior by means of post-tensioning. However, it is difficult to define the joint behavior of PT flat plate under vertical and lateral loads since there are limit experimental results. For this reason, the experimental study is undertaken to investigate the comparison of behavior of PT flat plate and RC flat plate, and how flat plate(Gravity Load Resisting System) is displaced as lateral loads, like the wind and the earthquake, are occur. The result of this experiment shows that PT flat plate is generally superior to RC flat plate in terms of controlling crack, postponing stiffness deterioration, energy dissipation, etc.