Advances in Fracture and Failure Prevention

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Authors: Tarek Qasim, Mark Bush, Xiao Zhi Hu
Abstract: This paper aims to assess the effect of shape irregularity on contact damage in a brittle coating on a stiff metal substrate. Hertzian contact damage in a dental porcelain layer over a Ni-Cr alloy substrate in both curved and flat geometries was studied using finite element analysis and experimental investigation. Three failure modes were examined with varying porcelain layer thickness: cone cracking at the top surface of the porcelain, interface cracking at the layer/substrate interface and plastic deformation below the contact area in the substrate. It is shown that curvature has very little effect on the initiation of surface cone cracks in this system, but substantial effect on the initiation of interface radial cracks. In particular, curvature reduces the critical load for the onset of interface cracks
Authors: Shigeru Aoki, Toshiyasu Nishimura
Abstract: Prevention method of delamination at adhesive layer during drilling of composite material using vibration is examined. First, this method is examined experimentally. As vibrational load, relatively low frequency vibration and ultrasonic vibration are used. It is concluded occurrence of delamination is less when vibration is used during drilling. Next, experimental results are examined by analytical method. Adhesive layer is assumed to be damping component. Condition of occurrence of delamination is proposed.
Authors: Young Doo Kwon, W.K. Choi, Hyun Wook Kwon, H.S. Choo
Abstract: The time-dependent distributions of temperature and stresses in a box-column welded from ultra thick plates with a center segregation were analyzed using the commercial finite element package SYSWELD+ for several types and angles of groove. The welding method used in the current study was SAW(submerged arc welding), which was initially simulated using the commercial finite element package MSC/MARC, combined with a user-defined subroutine, to identify the weld thermal cycle. The major points of investigation were the optimum type and angle of groove that would minimize the weld stress, especially at the center segregation. A nonlinear transient heat transfer analysis was accomplished. The thermal properties, i.e. conductivity and specific heat, were found to be temperature dependent, plus the effects arising from a phase change, convection, and radiation were also taken into account.
Authors: Ai Kah Soh, Jin Xi Liu
Abstract: This paper deals with a Mode III interfacial edge crack in a magnetoelectroelastic bimaterial subjected to line singularities such as an out-of-plane line force, a line electric charge, a line magnetic charge and a straight screw dislocation. The surfaces (including crack surfaces) of the bimateral are assumed to be electrically open and magnetically closed. The closed-form analytical solution to the problem is obtained by employing the complex variable approach in conjunction with the conformal mapping technique. The intensity factors of stress, electric displacement and magnetic induction are given explicitly. The obtained results can be used as the Green's function to solve more complicated problems.
Authors: Thongchai Fongsamootr, Charoenyut Dechwayukul, Notsanop Kamnerdtong, Carol A. Rubin, George T. Hahn
Abstract: Riveted lap joints are widely used to assemble complex structures, e.g. aircraft fuselages. A thin layer of adhesive (sealant), is normally applied to lap joints in order to restrict the entry of moisture and retard corrosion. In this work, combined adhesive-riveted lap joints were studied to understand the effect of three parameters: panel thickness, adhesive stiffness and adhesive layer thickness, on single row non-countersunk riveted lap joints. Finite element analysis (FEA), along with Thin Adhesive Layer Analysis (TALA-developed for simulating the adhesive layer in lap joint models), were used to analyze the joint behavior. In previous studies, the stress concentration factor for single row riveted lap joints was found to be approximately 6.1, and the stress concentration factor for sealed riveted lap joints was approximately 5.2 for a 180 micron thick sealant layer. In this study, panel thickness, adhesive stiffness and adhesive layer thickness were varied parametrically in FEA analyses to determine their affects on the joints. The FEA/TALA results were used to predict the fatigue life of the joints as functions of the three parameters. The results show that the maximum tensile stress is smaller with a smaller panel thickness. The results also showed that the stress concentration factor in the joints was reduced when the stiffness of the adhesive layer was increased or when the thickness of the adhesive layer was decreased. Finally, fatigue tests showed that the fatigue life of the combined adhesive-riveted lap joints was greater than for riveted lap joints without adhesive.
Authors: Do Won Seo, Ho Chel Yoon, J.Y. Lee, Jae Kyoo Lim
Abstract: The bonding strength of adhesive joints is influenced by the surface roughness of the joining parts. However, the magnitude of the influence has not yet been clarified because of the complexity of the phenomena. In this study, it is showed that surface treatment affects adhesive strength and durability of aluminum/polycarbonate single-lap joints, and loading speed affects tensile-shear strength of adhesive joints. To evaluate the effect of surface treatments on the adhesive strength, several surface treatment methods are used, that is, cleaning, grinding, SiC polishing and sand blasting. It is showed that an optimum value of the surface roughness exists with respect to the tensile-shear strength of adhesive joints. The adhesive strength shows linear relationship with the surface roughness and loading speed. And the mechanical removal of disturbing films of lubricants, impurities and oxides make adhesive strength increase significantly.
Authors: Jae Yeol Kim, Jae Ki Sim, M.J. Song, Chang Hoi Kim, Lee Ku Kwac
Abstract: Availability of defect test algorithm that recognizes exact and standardized defect information in order to fundamentally resolve generated defects in industrial sites by giving artificial intelligence to SAT(Scanning Acoustic Tomograph), which previously depended on operator’s decision, to find various defect information in a semiconductor package, to decide defect pattern, to reduce personal errors and then to standardize the test process was verified. In order to apply the algorithm to the lately emerging Neural Network theory, various weights were used to derive results for performance advancement plans of the defect test algorithm that promises excellent field applicability.
Authors: Dong Cheon Baek, Tae Sang Park, Soon Bok Lee
Abstract: Electroplated nickel manufactured via the LIGA process, offers the possibility of stronger structure and connectors in a micro electro mechanical systems (MEMS). In this study, the mechanical properties of electroplated Nickel thin film were characterized using two methods; tension test and nano-indentation test. In tension test, a linear guided motor was used as actuator and the applied force was measured using a load cell. Strain was measured with a dual microscope that obtains the displacement of two separated zone by the tracking process of the image captured with CCD camera. In indentation test, elastic modulus was measured using a CSM(continuous stiffness measurement) module. Two types of specimen were prepared in the same wafer and tested after four months of aging, which reduces the variation of properties caused by fabrication condition and aging effect. The tension specimen is 15 µm thick and 300 µm wide. The indentation specimen is also 15 µm thick. Young's modulus were measured by two different testing methods and compared quantitatively.
Authors: Zong De Liu, Kun Yang, Shu Lin Bai, Peng Duan
Abstract: The high velocity spraying experiments for preparing WC-Co ceramic coatings were carried out by using an electro-thermal explosion directional spraying device. The transient parameters of both the discharge circuit and the voltage applied to the WC-Co sheet were measured. Velocity of the shock wave in the explosive spraying nozzle was approximately measured and that was described with a one-directional piston model. The velocity of molten particles of WC-Co ceramics was estimated to be about 3162m/s. The microstructures and micro-hardness of the WC-Co coating, the interface between the coating and substrate were analyzed in details. The visible WC grain diameter of the coating ranges from 70 to 350nm, and the average value is 195nm. A metallurgical bonding layer with a thickness of about 1 was found at the interface. The values of micro-hardness of the coating are 1-1.4 times of the original one, and the micro-hardness near the interface is much higher than that of the substrate
Authors: Kenji Kaneko, Akira Ohmori, T. Hiraishi
Abstract: Fracture strength of WC-12Co thermal sprayed coating is investigated experimentally and analytically. In the experiments, one pair of butt cylindrical specimen with coating is subjected to combined tension with torsion stresses. Fracture loci were obtained for three kinds of thickness of the coating in σ-τstress plane. Stress distributions at crack tip singular point on fractured surfaces are analyzed by Finite-Element-Method and approximated by the expression σ=KR-λ where R means normalized thickness coordinate. It is found that the normal stress distributions are common to all cases of testing stress conditions and so fracture condition of the brittle coating is represented as K≧Kcr in the normal stress distribution even under mixed deformation mode I and III. A critical shear stress distribution for separation could also be obtained

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