Key Engineering Materials Vols. 297-300

Abstract: An effective way to reduce the weight of vehicle body seems to be application of new materials, and such trend is remarkable. Among the various materials for vehicle body, stainless steel sheets and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life fatigue design criteria for body structure, it is necessary to assess spot weldability and fatigue strength of spot welded lap joints fabricated under optimized spot welding condition. In this paper, spot weldability of stainless steel sheets, STS304L and STS316L, and cold rolled steel sheets, SPCC and SPCD. Fatigue strength of lap joints spot welded between similar and dissimilar materials were also assessed.

Abstract: Bogie is the connection device between carbody and wheel in railway vehicles. It is the core part that exert a important effect on the passenger safety and running safety. Bogie largely consists of the bogie frame, suspension, air brake system and wheel set. A static and dynamic load have acted on it complexly. When the bogie is designed, a finite element method, static load test, fatigue test, running test should be considered. A welded structure type bogie was developed for high speed freight car. But some bogie frames have the problems in end beam. There were some cracks ine end beams. The crack situation of the end beam have a bad effect on the brake system. In that case, the cars would be in danger of derailment. This report shows the cause of end beam crack, improvement method. In order to clear the crack cause, many tests were tried. The test result concludes that the crack cause of the end beam is not the brake load but the vibration at the real line running on the track. It is estimated that the improved car which end beam was reinforced was safe enough within permitted life of the car (25years). On the basis of the results, the existing end beam was improved. The safe of the improved end beam was proved by real line test on the track. The operation of freight car have no problems any more.

Abstract: The study for strength calculation of one way fiber-reinforced composites and the study measuring precisely fiber orientation distribution were presented. However, because the DB that can predict mechanical properties of composite material and fiber orientation distribution by the fiber content ratio was not constructed, we need the systematic study for that. Therefore, in this study, we investigated what effect the fiber content ratio and fiber orientation distribution have on the strength of composite sheet after making fiber reinforced polymeric composite sheet by changing fiber orientation distribution with the fiber content ratio. The result of this study will become a guide to design data of the most suitable parts design or fiber reinforced polymeric composite sheet that uses the fiber reinforced polymeric composite sheet in industry spot, because it was conducted in terms of developing products. We studied the effect the fiber orientation distribution has on tensile strength of fiber reinforced polymeric composite material and achieved this results below. We can say that the increasing range of the value of fiber reinforced polymeric composite’s tensile strength in the direction of fiber orientation is getting wider as the fiber content ratio increases. It shows that the value of fiber reinforced polymeric composite’s tensile strength in the direction of fiber orientation 90° is similar with the value of polypropylene’s intensity when fiber orientation function is J= 0.7, regardless of the fiber content ratio. Tensile strength of fiber reinforced polymeric composite is affected by the fiber orientation distribution more than by the fiber content ratio.

Abstract: Authors have developed an electric resistance change method for delamination monitoring of carbon/epoxy composite laminates. The method employs reinforcement fibers as sensors; electrodes are co-cured. Co-cured electrodes for delamination monitoring are adopted in the present study as sensors for monitoring the degree of cure. This study proposes a new method using electrical capacitance change for monitoring the degree of cure without using additional sensors. Applying alternating current between electrodes during the cure process provides dielectric properties of carbon/epoxy composites. As with the conventional cure monitoring method using extra dielectric sensors, the degree of cure of composites is monitored by measuring the dielectric constant of composites. The dielectric constant of epoxy resin changes concomitant with change of frequency of applied alternating current (AC). Using dependency of the applied AC frequency of the dielectric constant, the degree of cure is measured directly. The proposed method is applied to single and multi-ply carbon/epoxy composite laminates. The method demonstrates excellent estimations of the degree of cure without additional sensors.

Abstract: Effect of resin content on the mechanical properties of satin carbon fabric/epoxy composites is studied in this paper. Mechanical properties of the satin carbon fabric/epoxy composites are experimentally measured. The compressive strength and conversion ratio of strength of carbon fiber in the fabric composites are measured and compared with the experimental data of composite laminates reinforced by unidirectional fiber tape.

Abstract: In present study, we clarify the micro- to mesoscopic deformation behavior of semicrystalline polymer unit cell by using large deformation finite element homogenization method. Crystalline plasticity theory with penalty method for enforcing the inextensibility of chain direction and nonaffine molecular chain network theory were applied to the representation of the deformation behavior of crystalline and amorphous phases, respectively, in composite microstructure of semicrystalline polymer. The different directional tension and compression are applied to the 2- dimensional plane strain semi-crystalline unit cell model. A series of computational simulation clarified highly anisotropic deformation behavior of microstructure of semi-crystalline polymer, which is caused by rotation of chain direction and lamella interface, and manifests as a substantial hardening/softening. This anisotropy for tensile deformation is higher than that for compressive deformation.

Abstract: The mechanical properties of polymers are strongly influenced by meso-scale (10-9-10-3 m) structure such as entanglement, molecular weight distribution, orientation, etc. It is well known that sunlight induces the UV degradation of polymers. The mechanical properties of polymer are strongly influenced by UV irradiation because of chemical change of meso-scale structure. However the detail relationship between the mechanical properties and chemical change of meso-scale structure is not clear. In this study, it is aimed to clear this relationship by the simulation. Network models considered the meso-scale structure are constructed. Degradation is described to delete the chain elements in the network model. Large strain deformation of these network models is evolved via molecular dynamics analysis improved by us. It is possible to describe the degradation by this method.

Abstract: In this paper, the TiNi fiber reinforced/PMMA (Poly methyl methacrylate) composite is developed, and its effectiveness of controlling fatigue crack growth is studied. The TiNi fiber reinforced/PMMA composite’s mechanical property enhancement and deformation resistance are also studied. The fatigue behavior and crack propagation are observed with a SEM servo-pulser (fatigue testing instrument with scanning electron microscope) while increasing temperature. As the results, it is confirmed that the fatigue life and resistance are improved. How the shape memory effect and expansion behavior of the matrix caused by temperature increasing affect the fatigue crack propagation control is examined. It is verified that the control of fatigue crack growth is attributed to the compressive stress field in the matrix due to shrinkage of the TiNi fibers above austenitic finishing temperature (Af).