• Journal of the Korean Society of Safety
• /
• v.1 no.1
• /
• pp.41-49
• /
• 1986

Modern technological progress demands the use of materials at high temperature and high pressure. One of the most critical factors in considering such applications-perhaps the most critical one-is creep behavior. In this study the activation energy for the creep rupture (Qf) and the stress dependence of rupture time (n') have been determined during creep of Al 7075 alloy eve, the temporature range of $200^{\circ}C to 500^{\circ}C$ and stress range of 0.64 kgf/$\textrm{mm}^2$ to 9.55 kgf/$\textrm{mm}^2$, respectively, in order to investigate the creep-rupture property. Constant load creep tests were carried out in the enperiment At around the temperature $210^{\circ}C~390^{\circ}C$ and the stress level 1.53~9.55(kgf/$\textrm{mm}^2$), the stress dependence of rupture time(n') had the value of 6.6~6.78 but at 50$0^{\circ}C$, the value of 1.3. Besides at around the temperature of $200^{\circ}C~500^{\circ}C$ and under the stress level of 0.89~8.51 (kgf/$\textrm{mm}^2$), the activation energy for the creepprupture (Qf) was nearly equal to that of the volume self diffusion of pure aluminum (34Kca1/mo1e)

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.447-452
• /
• 2001

An automated system is developed to perform fatigue crack growth tests under constant effective stress intensity factor range ${\Delta}K_{eff}$. In the system, crack length and crack opening load are measured in real-time by using the unloading elastic compliance method. The system consists of two personal computers, an analogue electrical subtraction circuit, a stepping motor, a stepping motor driver, a PIO board, and the application software used to integrate the whole system. The performance of the developed system was tested and discussed performing constant ${\Delta}K_{eff}$ crack growth tests on a CT specimen of 7075-T6 aluminum alloy. The performance of the system is found to be strongly dependent on the accuracy of measurements of crack opening load. Besides constant ${\Delta}K_{eff}$ testing, the system is expected to be successfully applied for automation of various fatigue tests.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.12
• /
• pp.2090-2095
• /
• 1997

The plane stress fracture toughness for thin aluminum alloy(2024-T3 and 7075-T6) specimens are characterized by using compact-tension (CT) specimens. Anti-buckling plates were fabricated on both sides of the thin CT specimens to prevent the buckling phenomena which caused by the 45.deg. C plastic yielding at the crack tip under the plane stress condition. The plane stress fracture toughnesses determined by three different procedures are compared with each others. The plane stress fracture toughnesses are also compared with a few published values which were determined by using center-cracked panel specimens.

• Journal of the Korean Society for Precision Engineering
• /
• v.18 no.12
• /
• pp.124-129
• /
• 2001

Recently, life cycle and lead-time of products have been shortened with the demand of customers. Therefore, it is important to reduce time and cost at the step of manufacturing trial molds. High speed machining can be applied for this kind of purpose with a lot of practical advantages. In our research, several fundamental experiments are carried out to obtain machining parameters such as cutting force, machining time and surface characteristics for tool paths that are appropriate to high-speed machining. Moreover, a trial mold for an automatic transmission knob is fabricated with aluminum-7075 material. Using automatic set-up equipments, an ABS rapid prototype of a trial product of an AT knob is also manufactured with a filling process.

• Steel and Composite Structures
• /
• v.47 no.3
• /
• pp.395-403
• /
• 2023

The main objective of this article is to investigate the response of different fiber metal laminates subjected to low velocity impact experimentally and numerically via finite element method (FEM). Hence, two different fiber metal laminate (FML) samples (GLARE/CARALL) are made of 7075-T6 aluminum sheets and polymeric composites reinforced by E-glass/carbon fibers. In order to study the responses to the low velocity impacts, samples are tested by drop weight machine. The projectiles are released from 1- and 1.5-meters height were the speed reaches to 4.42 and5.42 meter per second and the impact energies are measured as 6.7 and 10 Joules. In addition to experimental study, finite element simulation is done and results are compared. Finally, a detailed study on the maximum deflection, delamination and damages in laminates and geometry's effect of projectiles on the laminate response is done. Results show that maximum deflection caused by spherical projectile for GLARE samples is more apparent in comparison with the CARALL samples. Moreover, the maximum deflection of GLARE samples subjected to spherical projectile with 6.7 Joules impact energy, 127% increases in comparison with the CARALL samples in spite of different total thickness.

• Transactions of Materials Processing
• /
• v.32 no.2
• /
• pp.92-99
• /
• 2023

In this study, shear fracture specimens are designed using finite element analyses for the characterization of ductile fracture criteria of metal sheets. Many recently suggested ductile fracture criteria require experimental fracture data at the shear stress states in the model parameter identification. However, it is challenging to maintain shear stress states in tension-based specimens from the initial yield to the final fracture, and the loading path can be different for the different materials even with the same shear specimen geometries. To account for this issue, two different shear fracture specimens for low ductility/high ductility metal sheets are designed using the sensitivity tests conducted by finite element simulations. Priorly mechanical properties including the Hosford-Coulomb fracture criterion of the aluminum alloy 7075-T6 and DP590 steel sheets are used in the simulations. The results show that shear stress states are well-maintained until the fracture at the fracture initiation points by optimizing the notch geometries of the shear fracture specimens.

• Journal of Practical Engineering Education
• /
• v.14 no.1
• /
• pp.119-125
• /
• 2022

Materials used for education are materials such as SM20C, Al6061, and acrylic. SM20C materials are carbon steel and are often used in certification tests and functional competitions, but are also widely used in industrial sites. The Al6061 material is said to be a material that has lower hardness and stronger flexibility than carbon steel, so it is a material that generates a lot of compositional selection of tools. If students are taught practical training using acrylic materials, vibration occurs due to excessive cutting in some parts and damage to the tool occurs. In this process, we examine to what extent the impact on the 2NC head, which is a five-axis equipment, can affect precision control. The weakest part of the five-axis equipment can be said to be the weakest part of the head that controls the AC axis. When the accuracy and cumulative tolerance of this part occur, the accuracy of all products decreases. Therefore, the core part of the 2NC head, the spindle housing, was carried out using an Al7075 T6 (Alcoa, USA) material. In the process of vibration and cutting applied to this material, the analysis was conducted to find out the value applied to the finite element analysis under extreme conditions. It is hoped that this analysis data will help students see and understand the structure of 5-axis machining rather than 5-axis cutting.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.3
• /
• pp.581-593
• /
• 1990

A semi-solid alloy in which solid and liquid phase are co-existing is obtained by strirring of Al7075 molten metal. A semi-solid alloy is dependent on the corresponding temperature within the solid-liquid range, and the process parameters should be controlled accurately to obtain the homogeneous semi-solid alloy. The possibility o homogeneous fiber-reinforce aluminum alloy by addition of $Al_{2}$O$_{3}$ short fibers with vigorous agitation was investigated. The billet of composite materials was fabricated by squeeze casting, and homogeneous dipersion state of fibers in billet of fabricated metal matrix composites was observed. A slurry of semi-solid short fiber metal matrix composites is used in the direct rolling process, and this process showed the fabrication possibility of metal matrix composite sheets. The fabricated sheet was tested regarding vickers hardness, elongation and micro-structure. It has become clear that mashy state processing and working are very useful to obtain parts of composites material closed to near net shape.