Papers by Keyword: Stress

Abstract: Piezoelectric ceramics possess very high piezoelectric coefficients but lacks the conformability for using them in flexible devices, in high-resolution sensing devices that can be integrated to human skin and other such applications. This problem can be resolved by blending them in appropriate proportion with polymers which are intrinsically light weight, stable and flexible. In this paper polymer composites xPZT– (1-x) PVDF (x= 0, 0.025, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared by solution casting method and their dielectric and its mechanical properties were studied. Given that PZT has a very high dielectric value, the composite's dielectric constant grew as the filler concentration increased which shows better dipole alignment in the composite. With an increase in filler concentration, the composite loses flexibility and tensile strength. Due to their greater Young's modulus than pure PVDF film, the films with compositions x=0.025 and x=0.05 could have better piezoelectric characteristics.

Abstract: X-Ray diffraction measurements of lattice parameter were performed for (111) and (100) oriented 3C-SiC/Si epiwafers. Strain of 3C-SiC epilayer and Si substrate were estimated and the result was compared with routine wafer deformation measurements. An unexpected discrepancy was observed between XRD and curvature measurements for (100) oriented samples.

Abstract: 8 inch 4H-silicon carbide (SiC) development faces challenges first from obtaining high-quality 8 inch SiC seed substrate, then reducing grown-in crystal residual stress and defects in the following crystal growth process. Here we report the diameter expansion process from 6 inch 4H-SiC seed substrate to 8 inch 4H-SiC crystal. Based on simulation and experimental results, it is deduced that an optimized radial temperature gradient (RTG) zone in the range of 0.10-0.12 °C/mm is essential for high-quality and efficient SiC crystal diameter expansion. According to the RTG calculation, diameter expansion process is designed and 8 inch 4H-SiC crystal as well as seed substrate is achieved. With the obtained seed substrate, high-quality 8 inch 4H-SiC crystal is developed and the following polished 4H-SiC substrate quality is characterized.

Abstract: A method for mitigating loss of conformational stability in 150 mm n-type 4H SiC wafers was investigated. Modifications to the physical vapor transport (PVT) process used to grow the parent bulk crystals, combined with post-growth thermal treatment, were examined as means of reducing the internal stresses hypothesized to promote instability. The magnitude of the stresses was analyzed by mechanically thinning sets of wafers produced from each process to determine the critical thickness of stability loss. The average critical thickness was found to be reduced by 13% via growth cell modification, at a reduced level of thermal treatment relative to a control process, with all wafers becoming unstable greater than 30 μm below the minimum recorded production thickness. Assessment of the spatial uniformity of dislocations indicated that lower conformational stability corresponded to elevated densities of basal plane dislocations (BPDs) and threading edge dislocations (TEDs) at the wafer edge relative to the center.

Abstract: To prevent arrays of basal plane dislocations (BPD) forming during grown 4H-SiC single crystals, the growth cell in physical vapor transport (PVT) growth was modified by adapting the temperature gradients, the seed attachment method and the seeding phase. The resulting reduction in stress was modeled numerically and the crystals were investigated by X-ray topography (XRT) and molten potassium hydroxide (KOH) etching. Due to these modifications, the formation of BPD arrays was completely suppressed.

Abstract: The failure occurred in the camshaft of the minibus vehicle after 14 years of use and a failure analysis was carried out to find the cause. The purpose of this paper is to simulate a failed camshaft by evaluating stress and fatigue using the ANSYS structural static approach to find the cause of the failure. Camshaft meshed with a size of 5 mm for the outer part of the fracture and 3 mm on the fracture. The load given is force (1400 N) and torque (113 Nm) and the support is fixed support on the second bearing. The stress shows that the applied load does not because fracture based on the theory of maximum normal stress and Mohr's criteria, the location of the highest and lowest stresses is not in the fault area, and fatigue life without defects produces infinite cycles or will not fail, and fatigue life simulation with defects results in a reduction in life. Based on these parameters, failure is caused by defects in the fractured part with an indication of the location of the fracture beyond the greatest potential for fracture and lower fatigue life.

Abstract: Aluminum Oxide thin films are potential candidate for anti-reflection, anti-soiling, and self-cleaning applications for solar cell panels, solar water heating panels, exterior windows of buildings, glasses, car windows, fabrics, and clothes. This paper reports on effect of chopping during deposition on the intrinsic stress and adhesion of Al₂O₃thin films deposited by electron beam evaporation. The kinetics of the growth and structure of the thin films is governed by adhesion. The durability and its wear are related to the certain extent adhesion of the thin film to the substrate. Effect of ambient aging on the adhesion and the internal stress in the films are also reported. The effect of chopping the thin film growth, phase change and presence of Al₂O₃ studied using scanning electron microscopy (SEM) and x-ray diffraction (XRD). The accumulation of strain energy in the thin film appears as internal stress and the binding of the vapor atoms to the substrates is referred to as adhesion. In this work, adhesion of thin films measured by direct pull off method and the internal stress is measured by interferometric method.

Abstract: This research analyzed the causes of failure in the leaf spring of a cold diesel Dump Truck. The test was conducted in the form of hardness using the Rockwell method and a hardness value of 104.8 HRB while microstructure analysis was used to view and identify fracture surfaces through SEM and optical microscope. Furthermore, the distribution of each spring load was determined by analytical analysis and found to be 28983 N while the chemical composition was analyzed by comparing the spring microstructure with the AISI 5150 standard. The finite element analysis conducted with the FEMAP software showed the maximum stress and strain values in the leaf spring were recorded on the left and right sides. The stress intensity factor (K_I) around the end of the initial crack was also found to be greater than the fracture toughness of the material (K_IC), thereby, causing the initiation and propagation of cracks in the leaf springs. It was, therefore, concluded that the failure in the spring was due to an initial defect caused by the dynamic load experienced by the spring, thereby, leading to the initiation and propagation of cracks up to the final fracture.

Abstract: The primary purpose of the structural study on the 4.2-meter-long Jaloe Kayoh boat is to analyze the FEA of E-glass and ramie fiber composites, as well as the polyester resin. The hand lay-up method was used in this study to manufacture specimens following the ASTM D638-02 standard, while the tensile test was performed under the ASTM D790-02 standard. Based on the simulation results, the data analysis method was used to visualize the relationship between the stress and strain strength parameters on the structure, as well as a reaction force and displacement, which were related to the centralized loading on the walls and hull of the Jaloe Kayoh boat with a minimum loading variation of 539.3 N and a maximum loading variation of 2157.4 N. The maximum loading of the stress strength on the hull wall of Jaloe Kayoh was obtained at a load of 220 kg or 2157.4 N. The stress values obtained were 4.212e+09 N/mm2 for E-glass fiber and 3.998e+09 N/mm2 for ramie fiber. The highest Reaction Force values obtained were 4.369e+03 N for E-glass and 4.952e+03 N for ramie fiber. The highest displacement value was obtained, which was 2.620e-02 m for E-glass fiber and 2.662e-02 m for ramie fiber. Based on the simulation results, E-glass and ramie fibers are still safe and feasible to use as a base or initial layer, or one of the supporting layers, for lamination on one of the materials for the Jaloe Kayoh boat's walls and hull.

Abstract: Today, there are many different types of shaped steel with different characteristics, designed to meet the different needs of modern buildings. The most common is H-shaped steels, I-shaped steels and V-shaped steel. Shaped steel is hard and durable, with high tensile strength, and can withstand strong vibrations. When subjected to harsh conditions due to the impact of chemicals, the temperature should be kept suitable for industry and construction. Beams are designed for strength, so that they can resist the internal shear and moment developed along their length. To design a beam in this way requires the application of shear and flexure formulas, provided the material is homogeneous and exhibits linear elastic behavior. Although some beams may also be subjected to axial force, the effects of this force are often neglected in design, since it is generally much smaller than the stress developed by shear and bending. To optimize the design of the I-beam, the CAD model was developed in Inventor Professional 2019, and we used the Shape Generator module to determine the best design. In addition, these models also employ finite element analysis to determine whether the designs created are safe. This research also aims to assess long-standing traditional structures.