查看更多>>摘要：In this study, the effect of water absorption on mechanical properties of hemp fiber reinforced green composite(HGC) was examined. Plain woven hemp fabric was used as reinforcement. Emulsion type biodegradable resin was used as matrix. The composite was made by compression molding method. Water absorption rate and the effect of the ratio on the mechanical properties were examined. Following results are obtained. The water absorption rale increased with an increase of absorption time. The water absorption rate had an equilibrium state within 30 days. The duration was not dependent on fiber content. In the case of that specimen was kept in water 182 days, the strength decreased 70% of the ultimate one. But in the case that the specimen has dry process after water absorption process, the strength recovered 57%. The recovery ratio is not dependent on water absorption time. The strength reduction rate after dry process is not dependent on fiber content. The strength of resin decreased 62%, and the strength of fiber decreased 13% by water absorption, So the strength reduction of the composite is due to the effect of matrix.
查看更多>>摘要：Two important factors in damage tolerance engineering are the damage size that can be tolerated and the use of applied nondestructive testing (NDT) technique for detection of defects. Generally, NDT of large mechanical structures, such as vessels and pipes in nuclear power plants, is carried out according to national codes, and the damaged mechanical parts detected during periodic NDT are repaired or replaced after the evaluation. However, unexpected accidents can occur if cracks in the structure grow and exceed the tolerance limit during operation. Therefore, there is a need to develop NDT techniques that can detect micro-damage in the vessels and pipes. In this paper, we propose a cylinder-type magnetic camera to fill this need. We use a cylindrically integrated Hall sensor array (CIHaS) as a magnetic sensor to create magnetic images, and we use a solenoid coil as the source of the magnetic field detected by the magnetic camera in order to achieve high crack-detection ability. The proposed method is tested with an examination of the cracks on a prepared pipe sample.
查看更多>>摘要：Wheels are essential parts of an express train, as they support the train's weight, but because of the limited time available for testing and repair in the maintenance factor}', the 1000 wheels of each high-speed train must be tested within 1 h. Therefore it is essential to develop a new NDT system that is able to (a) detect cracks quickly and (b) provide high crack-detection ability regardless of the state of the materials. In this paper we propose a scan-type magnetic camera to satisfy this need. We use a linearly integrated Hall sensor array (LIHaS) as a magnetic sensor to make high-speed testing possible, and we use a small, yoke-type magnetizer as the magnetic source for the magnetic camera to assure high crack-detection ability. We tested the method by examining the cracks on a sample wheel traveling at 27.5km/h.
查看更多>>摘要：Thermal banner coatings (TBCs) have been employed for the insulation of substrates from high temperature in gas turbine plants. The TBC system consists of ceramic top coating, metallic bond coating and substrate. Delamination of the ceramic coating is important problem in TBC systems. In this paper, the delamination mechanism was studied by residual stress history under thermal aging and thermal cycle conditions. In-plane residual stress histories of ceramic coating and bond coating after thermal aging and cycling were measured by X-ray diffraction method. The residual stress under thermal cycling was also calculated by FEM analysis. The results obtained were as follows: (1) in-plane surface residual stresses of the coatings scarcely changed regardless of the increase of thermally grown oxidation (TGO). (2) high compressive thermal stress, residual stress at room temperature, in ceramic coating induced by thermal stress did not occur. It was found that stress of ceramic top coating was relaxed by micro cracks and driving stress of delamination was in-plane high compressive stress.
查看更多>>摘要：The purpose of this paper is to discuss the plastic deformation and pressure reversal of pipe during hydrostatic testing. The higher the test pressure, the smaller the number of defects that remain undetected. In order to study the effect of hydrostatic testing, full scale burst experiments were carried out with API 5L X65 SSAW pipes of 660mm outside diameter and 12.5 mm wall thickness. Nine spiral oriented deflects had been machined in the weld. Deformations of deflects were measured. The pressure reversal was computed. It can be concluded that if a hydrostatic test can be successfully accomplished without the failure of any defect, the likelihood of a pressure reversal will be extremely small.
查看更多>>摘要：To check the structural strength of the body of the newly-made container freight car, load was added to the underframe of the container freight car. The objective of this study is to evaluate whether or not the underframe of a freight car under the maximal strength is safe. A freight car for transporting railroad freight is usually designed and made of SM490YA steel and SM490Y steel. The carbody of rolling stock is a principal structure that supports major equipment of the underframe and the container 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 freight car. The strain gauges were attached on the carbody based on FEM results. The actual vertical loading test and horizontal compression loading test were conducted. The test results showed that the carbody is safe under the condition of the designed load.
查看更多>>摘要：An experimental investigation was performed on mode I delamination of z-pinned double-cantilever-beams (DCB) and associate z-pin bridging mechanisms. Tests were performed with ten types of samples: (1) big-pin reinforced DCB (double-cantilever-beams) with three areal densities D=2.01%, 5.15%, 8.04%, respectively; (2) median-pin reinforced DCB with three areal densities D=0.85%, 2.17%, 3.40%; (3) small-pin reinforced DCB with three areal densities D=0.25%, 0.63%, 0.90% and (4) without pin reinforced DCB specimens. Delamination tests samples were prepared from unidirectional continuous carbon libre/epoxy prcprcg (T300/TDE86), made into 3 mm thick unidirectional laminates with and without a block of Z-pins in the crack path. Fracture testing was carried out under Mode 1 (standard DCB test). Experiments have shown that increases in debond resistance and ultimate strength depend on the material, size, density, location of the pins and the mechanisms of pin deformation.A finite element (FE) model is developed to investigate mode I delamination toughness of z-pin reinforced composite laminates. The z-pin pullout process is simulated by the deformation of a set of non-linear springs. A critical crack opening displacement (COD) criterion is used to simulate crack growth in a DCB made of z-pinned laminates. The toughness of the structure is quantified by the energy release rate, which is calculated using the contour integral method. The FE model is verified for both unpinned and z-pinned laminates. Predicted loading forces from FE analysis are compared to available test data. Good agreement is achieved. The numerical results indicate that z-pins can greatly increase the mode I delamination toughness of the composite laminates.
查看更多>>摘要：In this study, we propose an interesting scheme for analyzing micro-pillar compression test results based on finite element method. It uses only load and displacement data measured by micro-pillar compression test, a framework of conventional incremental metal plasticity, and an iterative scheme for updating the material parameters. This is an inverse approach to determine the constitutive relation of materials based on experimentally measured load and displacement. As a demonstrative example, Ni-Co micro-pillars with a diameter of 10 μm and a height of 20 μm were fabricated by micro-machining process, and their load-displacement data were measured by a micro-pillar compression tester. Using the proposed scheme and the measured load-displacement data, the stress-strain curves for the Ni-Co micro-pillars were estimated.
查看更多>>摘要：The shapes and types of containers for foods, drugs and medicines, and cosmetics and detergent refills are diverse: glass bottles, cans, PET bottles and laminate-film liquid packaging bags are examples. In recent years, to increase the ease of pouring out the contents of laminate-film liquid packaging bags, the shape of the heat seal has been changed from a flat seal to a bottleneck seal. However, the large number of bottleneck seal ruptures of liquid packaging bags due to impact load during the transport, loading and unloading of packaged products has been a problem. In our previous study, we investigated impact peel strength in the heat-sealed area of a laminate film; however, the effects of the bottleneck seal shape and heat-sealed area width on impact peel strength and rupture occurrence have not yet been clarified. In this study, experiments were carried out to clarify the effects of the flat and bottleneck seal shapes, as well as heat-sealed area width, on impact peel strength and bag rupture occurrence. The following two films were used : (1) a multilayered laminate film with barrier characteristics against oxygen and water vapor, which is frequently used for liquid packaging bags owing to its high efficacy in food quality preservation, and (2) a multilayered laminate film without barrier characteristics. On the basis of the results obtained, we established, for the first time, a new standard regarding bottleneck seal shape and heat-sealed area width.
查看更多>>摘要：Thermal Barrier Coatings have existed for over 40 years, and with in the last 15 years their use in industrial applications has dramatically increased. Thermal Barrier Coatings (TBCs) are currently used in gas turbines, diesel engines, throughout aerospace and nuclear power industries. The purpose of TBC is to reduce temperature and thermal stresses, and. as a result, increase the reliability and life of load-bearing components subjected to high temperature or temperature flux. However, TBCs often fail under thermal cyclic loading with reliability still being the major issue impeding their wide-spread applications.The focus of this work is on experimental investigations of zirconia/nickel graded TBC system, subject to thermal shock loading. The graded TBC systems were fabricated utilising a recently developed slurry spray manufacturing technique. This is a robust technique, and is able to cover large and curved surfaces at low cost, and provides many advantages in comparison with its alternatives. This paper describes the developed technique and presents selected results of thermo-mechanical and fracture testing of the TBCs including graded coatings fabricated using this new technique.
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