Jae Mean Koo

Fatigue Damage Evaluation of Woven Carbon-Fiber-Reinforced Composite Materials by Using Fatigue Damage Model

. 하여 피로손상 누적곡선을 획득하고 해석하였다. Abstract: Owing to the high specific strength and stiffness of composite materials, they are extensively used in mechanical systems and in vehicle industries. However, most mechanical structures experience repeated load and fatigue. Therefore, it is important to perform fatigue analysis of fiber-reinforced composites. The properties of composite laminates vary depending upon the stacking sequence and stacking direction. Fatigue damage of composite laminates occurs according to the following sequence: matrix cracking, delamination, and fiber breakage. In this study, fatigue tests were performed for damage analysis. Fatigue damages, which have to be considered in fatigue analysis, are determined by using the stiffness values calculated from hysteresis loops, and the obtained fatigue damage curve is examined using Maos equation and Abdelals equation.

Prediction of Fracture Strength of Woven CFRP Laminates According to Fiber Orientation

CFRP composite materials have been widely used in various fields of engineering because of their excellent properties. They show high specific stiffness and specific strength compared with metallic materiasl. Woven CFRP composite materials are fabricated from carbon fibers with two orientation angles (0°/90°), which influences the mechanical properties. Therefore, woven CFRP composite materials show different types of fracture behavior according to the load direction. Therefore, the fracture behavior of these materials needs to be evaluated according to the load direction when designing structures using these materials. In this study, we evaluate the fracture strength of plain-woven CFRP composite materials according to the load direction. We performed tests for six different angles (load direction: 0°/90°, 30°/-60°, +45°/-45°) and estimated the fracture strength for an arbitrary fiber angle by using the modified Tans theory and harmonic function.

Study of Failure Criterion of Hole-Notched Plain-Weave Carbon Fiber Reinforced Plastic (CFRP) Composites

초록:CarbonFiberReinforcedPlastic(CFRP)복합재료는높은비강성및우수한화학적특성등으로인하여여러분야에서점점사용이증가하고있다.대부분의CFRP복합재료는여러부품들의조립을통해제작된다.이러한독립된부품들은볼트,핀등과같은기계적인방법을통해체결된다.볼트나핀에의한hole은구조내에서노치로작용하여부품의강도저하의원인이된다.본논문에서는홀의크기와시험편폭이노치재의파괴강도에끼치는영향을평가하여hole을포함하고있는평직CFRP복합재료의정하중파괴강도를실험적으로평가하였다.이를위하여본논문에서는홀크기와시험편폭에따른점응력조건의특성길이를평가하였으며,특성길이와노치재의파괴강도의관계를확인하였다.이를이용하여노치재의정하중파괴기준을재정의하였다.Abstract:Recently,carbonfiberreinforcedplastic(CFRP)havebeenusedinvariousfieldsbecauseofitshighspecific modulus, and chemical properties. Most products in which CFRP composites are used aremanufactured by joining the product components by bolts or pins. Holes for bolts and pins decrease thestrength of the components because these holes act as notches in the structures. In this study, the fracturestrength of CFRP plain-weave composite plates containing holes is experimentally investigated to examine theeffects of hole-size and specimen width on notched tensile strength. The results show that the characteristiclength considered in the point stress criterion depends on the hole size and specimen width. There exists acertain relation between notched tensile strength and characteristic length. Fracture criterion is redefined onbasisofthisrelation.

Welding Characteristic Evaluation of GMAW and Laser Cladding for the Gas Turbine 1st Blade

The advancement in superalloys permits the hot gas path components to operate for thousands of hours under severe centrifugal, thermal and vibratory stresses. The blade of a gas turbine must withstand the most severe condition combined of temperature, stress, and environment. After a long operation, the damaged blades of a gas turbine used are welded for build-up and repaired. We analyzed and compared the mechanical properties of GMAW(Gas Metal Arc Welding), a manual welding method, a laser cladding method, and an automatic welding method under research and development.

A Study on Thermal Fatigue Life Variation According to Thermal Exposure Time

Thermal barrier coating. Thermal fatigue. Exposure time. Thermal fatigue test is one of the most widely used method to evaluate the durability of thermal barrier coating (TBC). However, thermal fatigue test can be concluded in totally different results according to the test variations. Especially, Exposure time of thermal fatigue test can affect the delamination life cycle of TBC. In this study, using the same test equipment which Kim et al. used, thermal fatigue tests were performed with different holding time at high temperature, and the test results by Kim et al. and those by this study were compared. In addition, delamination map was come to perfection from the test results to define more accurate thermal fatigue life.

A Study of TMF Characteristics of Ni-Base Superalloy IN738LC

A gas turbine blade operates under severe conditions including high temperature, high speed rotation, and frequent starts and shutdowns. Under such operating conditions, a blade is exposed to a thermo mechanical fatigue environment. These conditions shorten the life of the turbine parts and reduce the reliability of the gas turbine. Therefore, research on the characteristics of blade material is necessary. In this study, thermo-mechanical fatigue (TMF) tests were conducted for IN738LC, which is base a material for turbine blades. Tests were conducted under both the IP (in-phase) and OP (out of-phase) conditions, and tests results were compared in terms of fatigue life. After obtaining the ε-N curves, additional TMF tests were conducted according to variations in fatigue life. The purpose of the TMF test is to observe the change in mechanical properties of materials damaged during TMF and how these relate to fatigue life. For this purpose, an indentation test was conducted and the relationship between hardness and fatigue life were obtained.

Durability Evaluation of Thermal Barrier Coating (TBC) at High Temperature

Thermal barrier coating (TBC) which protects the gas turbine from high temperature is damaged by repeated thermal fatigue [1,2]. Generally, damage of top coating of thermal barrier coating is resulted in damage to the entire gas turbine. Thus, the durability of the thermal barrier coating should be evaluated to protect the gas turbine from damage. In general, the major cause of delamination in the top coating is the thermal stress at its interface according to the change in temperature [. In this research, parallel stress at the top coating interface (S11) was verified as the major cause of delamination by finite element analysis. In order to evaluate the durability of the TBC, we need information about the parallel strength at the interface, but it is difficult to measure. Furthermore, we verified the relationship between the stress perpendicular to the interface (S22) and the stress parallel to the interface (S11) by finite element analysis. The durability of the thermal barrier coating was evaluated by comparison of the results of the bond strength test of Kim et al. with the results of the finite element analysis of this research.

Evaluation of Influence of Cracks on DVC Coating Using Finite Element Analysis

TBCs (Thermal Barrier Coatings) are one technique for assuring appropriate endurance in extreme environments. DVC coating is a type of TBC that is applied by the insertion of artificial vertical cracks in a TBC to reduce the possibility of coating fracture. This study evaluates the influence crack depth and the distance between cracks, which are the main parameters of DVC coating, by FEM (Finite Element Method).

Evaluation of Fatigue Characteristics of Rubber for Tire Using Strain Energy Density

Rubber, a hyperelastic material, is the main material used in tires. During the operation of a car, the tire receives various types of loads. The accumulation of strain energy due to such loads induces tire failure. Generally, because rubber materials used for tires have stress softening characteristics, unlike metals, test methods used for metals cannot be applied to rubber. Therefore, in this study, for the evaluation of the fatigue properties of two types of specimens that have different material components, a tensile test and a fatigue test according to the extended strain range dissimilar to ASTM D4482 are performed, and fatigue life equations are proposed based on the test results.

Evaluation of Residual Strength Under Impact Damage in Woven CFRP Composites

Damage induced by low velocity impact loading in aircraft composite is the form of failure which is frequently occurred in aircraft. As the consequences of impact loading in composite laminates, matrix cracking, delamination and eventually fiber breakage for higher impact energies can be occurred. Even when no visible impact damage is observed, damage can exist inside of composite laminates and carrying load of the composite laminates is considerably reduced. The objective of this study is to evaluate and predict residual strength behavior of composite laminates by impact loading and for this, tensile test after impact was carried out on composite laminates made of woven CFRP.