Key Engineering Materials Vol. 627

Abstract: Development of the Korean small scale aircraft (KC-100) has been carried out by KAI (Korea Aerospace Industry Ltd.) for the BASA(Bilateral Aviation Safety Agreement) program with FAA. The KC-100 aircraft adopted the environmental friendly whole composite structure concept due to low fuel consumption owing to its light weight. However the composite structure has a disadvantage. They are very weak against impact damage due to FOD (Foreign Object Damage). This study is to investigate the residual compressive strength of the carbon/epoxy fabric and UD (Unidirectional prepreg tape) laminate due to impact damages. This residual compressive strength test follows fully the ASTM standard test procedure. Experimental investigation results reveal the residual strengths and the damage mode and size of impact damage specimens. Through these tests, it is found that the residual strength of the impact damage specimens is greatly reduced in comparison to the undamaged specimens depending on increase of both the indentation depth and the impact energy. The size and shape of damage zone greatly affects the reduction of the compressive strength.

Abstract: This paper address the mechanical properties of high performance concrete exposed to hot weather in terms of compressive strength and the modulus of elasticity. The variable of this study is curing temperature of 35 °C and 50°C under hot weather condition.

Abstract: The truck that is used as running equipment for freight car support is a core structural part that supports the load of the car body and that greatly influences the safety of freights and vehicles, as well as their running performance. The running equipment is composed of truck frames, wheels and wheel axles, independent suspensions, and brakes. Among these components, the truck frame supporting the load of the vehicles and freights may be the most important one. This study was carried out to analyze the structure of truck frames and to determine whether they are safe when the maximum vertical load, breaking load, and front and rear loads are applied to them. This was done by subjecting the truck frames to stress tests and then measuring the stress on each of their parts. Before the load test, a structural-analysis program was used for the stress distribution analysis of the truck frame. To measure the stresses based on the results of the structural analysis, strain gages were attached to the surfaces of truck frames [1].

Abstract: To check the structural strength of the carbody of the newly–made gondola car, load was added to the underframe of the gondola car. The objective of this study is to evaluate whether or not the underframe of a gondola car under the maximal strength is safe. A gondola car for transporting railroad freight is usually designed and made of SM490YA steel and SS400 steel. The carbody of rolling stock is a principal structure that supports major equipment of the underframe and the freight. Therefore, the strength evaluation of this structure is important. Both structural analysis and loading test were performed under the loading condition. Prior to the evaluation of structural strength, finite element method software was used for structural analyses on stress distribution in a carbody of a gondola car. The strain gauges were attached on the carbody based on FEM results. A vertical load test, compressive load test, measurement of deflection amount and a natural frequency measurement test were conducted.

Abstract: This study developed the innovative slip-form system for the construction of concrete pylons. The slip-up time of the slip-form is determined by estimating the compressive strength from surface wave velocity by the device attached to the slip form. GPS and tiltmeter are applied to secure the precise construction quality. The design of the slip form is verified in advance by BIM to validate its applicability through virtual assembly and construction. A slip form system is fabricated and mockup test is conducted to verify the performances of the developed techniques through the construction of a 10 m-high pylon with hollow section.

Abstract: Fatigue behavior of Mg-Al-Ca-Mn alloy with T6 treatment was studied at room temperature and 150°C by conduction rotating bending fatigue test. Fatigue strength at high temperature was lower than that at room temperature in the alloys with and without heat treatment. However, degradation of fatigue strength at high temperature in the T6 treated alloy was not significant compared to the as-extruded alloy. Fatigue crack initiation and propagation behavior was observed with replication technique by conducting interrupted fatigue test at room temperature and 150°C. Multiple cracking was significantly observed at 150°C in both as-received and T6 treated alloys. Change in grain size and randomization of crystal orientation due to the heat treatment could affect the fatigue property.

Abstract: At higher loading rates, modified Hopkinson pressure bar apparatus is widely used to determine the dynamic fracture toughness of the engineering materials. For accurate measurement of the dynamic fracture properties, we need to thoroughly understand the contact situation of the three-point bend specimen, with the loading apparatus. Strong inertial effects complicate the specimen’s contact situation with impactor and supports. In this work, ANSYS software is used for modeling and analysis of a modified Hopkinson pressure bar loaded fracture experimental setup. Analysis of stress contours and nodal displacements are used for the examination of specimen contact state. The results indicate that during loading in the elastic range, the specimen remains in contact with the loading apparatus as this is previously proved experimentally.

Abstract: A series of tests for low cycle fatigue were conducted on the tubular specimens for 304 stainless steel under variable amplitude and irregular axial-torsional loading. Rainflow cycle counting and linear damage rule are used to calculate fatigue damage and four approaches, e.g. SWT(Smith-Watson-Topper), KBM(Kandil-Brown-Miller), FS(Fatemi-Socie), and LKN(Lee-Kim-Nam) approach are employed to predict the fatigue life. The maximum shear strain plane, the maximum normal strain plane, and the maximum damage plane are considered as the critical plane, respectively. The effects of the choice of the critical plane on previous approaches are discussed. It is shown that comparing with the maximum shear/normal strain approach, the predictions are improved by using the maximum damage plane approach, part nonproportional paths for SWT, AV and part nonproportional paths for KBM, TV paths for FS. But for LKN, the prediction results are nonconservative for some paths than that of the maximum shear/normal strain approach.

Abstract: Very high plastic strain zones with equivalent plastic strain above 0.2, PZ_0.2 and above 0.5, PZ_0.5 in 304 stainless steel small punch specimens loaded at RT to various level were observed and measured by martensite formation and recrystallization technique, respectively. It is found that both the very high plastic zones are formed ,at middle stage of the small punch test, at first near the outer surface region of the specimen where the loading ball is contacted to the specimen. The zones extend with increasing load toward the inner surface. Thus the contact area part of the specimen with the ball causes a significant strain gradient through thickness. This will be due to the constraint of the plastic deformation near the contact region by the friction force.

Abstract: The objective of this study was to determine whether subjective measurement of slipperiness could be used as an subsidiary mean which made up for the demerit of indicators (roughness and coefficient of friction) of slipperiness. Two subjective rating methods for evaluating slipperiness—the Analytic Hierarchy Process (AHP) and the Friedman test—were used to measure perception of slipperiness on seven different floor surfaces contaminated with detergent solution (SLS). Twelve subjects wore the same footwear and walked on self-selected steps and cadence along the test floors. The safety criteria obtained with perceived slipperiness was similar with that of ANSI/NFSI B101.1. There was a higher correlation (r = 0.99) between the Friedman test and Ramp test parameter except for ground steel. There was also a high correlation (r = 0.92) between the Friedman and R_z parameter except for ground steel plate and profiled tile. The results showed that the perceived slipperiness could be used as indicator of slipperiness and supplement objective measurement of slipperiness.