Finite Element Stress Calculations Research Articles

Influence of Friction Coefficient on the Performance of Cold Forming Tools

The automotive industry has undergone significant advancements and changes over time, resulting in the use of more complex parts in modern vehicles. As a consequence, the parts used in the manufacturing process are subject to higher stress levels, which reduce their service life. To mitigate this issue, surface treatments can be applied to improve the mechanical properties of the tools. In this study, we examined the impact of surface treatments on reducing tool stress during a cold forming process. The process involved reducing the thickness of a sheet from 6 mm to 2.5 mm, which generated high stresses in the tooling. We used finite element stress calculations to analyze the process and found that by reducing the friction coefficient to 0.1, tool stresses can be reduced by 20%, leading to an increase in tool life. Moreover, the press force and tool wear were also reduced by 18%. To validate the theoretical calculations, we performed field tests in a real manufacturing process.

STATIC TESTS OF FULL-SIZE ACOUSTIC PANELS OF AIRCRAFT GAS-TURBINE ENGINES

The article suggests the installation and methods of static tests for the limit working and fracture loads of acoustic panels of aircraft gas-turbine engines (GTE). It is not possible to perform the full scope of static tests on the engine as it is technically impossible to obtain the airflow pressures required by airworthiness standards. The required pressure in the proposed installation is created by the punch, which is the same shape as the panel to be tested. Flexible rubber sheets are used to equalize contact pressure on the panel surface. The similarity in the distribution of pressures on the surface of the acoustic panel created by the air flow as part of the GTE and the pressures created by the punch as part of the installation is confirmed by comparing the stresses and deformations obtained as a result of finite-element calculations. The article presents the results of certification static tests and flaw detection of a three-layer acoustic panel. Comparison of the results of finite-element calculations of stresses and displacements of the acoustic panel as a part of GTE and as a part of the installation has shown that in the latter case the estimations of static strength are conservative, which positively affects their safe operation.

Structural rigidity optimization with an initial design dependent stress field. Application to thermo-elastic stress loads

This paper presents a compliance optimization methodology considering an initial stress field. Assuming a local dependency of the initial stress with the optimization parameters, the obtained numerical procedure is composed of finite element stress calculations and local minimization problems that are solved analytically or using a simple bisection procedure. This optimization algorithm is then found to be numerically very efficient. Two optimization problems that fall in the scope of the proposed methodology are considered: topology optimization of the isotropic mixture of two isotropic linear elastic materials (one of the material possibly being void) and orientational optimization (i.e. distribution of anisotropy) with an orthotropic linear elastic material. Numerical examples illustrating the optimization methodology in the case of thermo-elastic stress loads are presented.

Design and stress analysis of in-vessel saddle coils for MHD control in ASDEX Upgrade

A set of in-vessel saddle coils for MHD control in ASDEX Upgrade is described. A conventional coil design is chosen which employs a five turn square cross-section copper conductor with central cooling bore embedded in an epoxy resin. The winding is enclosed in a solid metal casing, made of a thin deep-drawn inconel sheet in order to maximise the electrical resistance and minimise L / R and shielding of the magnetic field. The bending stress in the coil casing due to the mount is reduced by reinforcing ribs perpendicular to the current direction. Fatigue stresses are avoided by application of a pre-stress on the casing exerted by the mounting bolts. Finite element stress calculations are performed to verify the design. Secondary stresses induced by thermal expansion in the casing and the conductor are well tolerable. The structural stiffness of the coil design provides a high resonance frequency, above the operation frequency range f = DC … 1.2 kHz.

432 単結晶シリコンの曲げ試験における結晶異方性の効果(T09-2 微小機械システムにおけるマイクロ・ナノ力学(2) 単結晶シリコンの力学特性,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Single crystal silicon has a complicated anisotropic elasticity specific to single crystal materials. We have evaluated fatigue characteristics of micromachined single-crystal silicon using resonator devices with two crystallographic configurations. The fatigue strength of the <100>-oriented test piece showed about 1.5 times higher value compared with that of <110>-oriented one. The difference was analyzed using finite element stress calculations including proper crystal anisotropy effect. A stress relaxation effect by the elastic anisotropy was shown on the rounded notch structure. Moreover, the difference in the fatigue strength implied the importance of anisotropic fracture characteristics in single crystal.

Influence of focusing and signal shape on the efficiency of stone fragmentation in vitro under equal energy conditions

To investigate the mechanisms of fragmentation in lithotripsy, simulations and experiments were performed. Wave shapes deduced from measurements near the focus of a piezoelectric source were used as input signals for finite element calculations of stresses and strains in spherical stones of different sizes. The effects of strongly and weakly focused sound fields were compared to those of a plane wave assumption representing lithotripters with large focal widths. The energies of the fields were matched. In targets with diameters less than 6 mm the simulated tensile stresses induced by strong and weak focusing exceed those of the plane wave assumption. For in vitro experiments a double‐layered self‐focusing piezoelectric source was used. To represent lithotripters with different sound fields the signal shape was varied by changing the interpulse delay but maintaining the energy. The total number of pulses needed for fragmentation into particles smaller than 2 mm diameter was counted. At usually applied energies experimental results show that the numbers of pulses needed for complete fragmentation are almost independent of the signal shape. In conclusion, the results indicate that strongly focused lithotripters are in principle more effective than those with wide focal widths in breakage of small stones.

Mechanical behaviour of metallic thin films on polymeric substrates and the effect of ion beam assistance on crack propagation

The mechanisms of crack propagation in metallic films on polymeric substrates have been studied through in situ atomic force microscopy observations of thin films under tensile stresses and finite element stress calculations. Two series of films – ones deposited with ion beam assistance, the others without – have been investigated. The observations and stress calculations show that ion beam assistance can change drastically the propagation of cracks in coated materials: by improving the adhesion film/substrate, it slows down the delamination process, but in the same time enhances the cracks growth in the thickness of the material.

Design enhancements for stress relaxation in automotive multi-shell-structures

Recent attempt to enhance the safety against collision has reshaped the simple single-shell structure into the integrated multi-shell structure. Moreover, due to various regulations continuously tightened for environment, weight reduction of automobile becomes an increasingly important issue. Weight reduction is mainly accomplished by better redesign, adoption of lighter materials, and small-sizing of auto (parts). Focusing on the local redesign among three, we suggest local patching methods. We also present, as another way, a method of determining thicknesses of subpart-shells in an integrated multi-shell structure. Those redesign methods successfully bring a preset amount of stress relaxation. More specifically, we first select a cross member as local patching model. Based on the finite element stress calculations, we relieve the stress of cross member by patching in two ways––non-uniform thickness patching and optimized uniform thickness patching. The latter is more effective and practical. Selecting a box type subframe as other redesign model, we determine the thickness of each subpart-shell by axiomatic design approach. The patching methods and the axiomatic approach of this work can be extended to the other multi-shell structures such as center member and lower control arm.

Design Enhancements for Automotive Integrated Shell Structures

Recent attempt to enhance the safety against collision reshaped the simple shell structures into the integrated complex shell structures. Moreover, due to various regulations continuously tightened for environment protection, weight reduction of automobiles becomes an increasingly important issue. Auto parts lightening is mainly accomplished by more reasonable design, adoption of lighter materials and miniaturization of the auto bodies. Focusing on the locally enhanced design approach among the above three ways, we here attempt to develop a patching optimization method, and also to determine the thicknesses of an integrated shell structure, both bringing a specified amount of stress relaxation. We first select a cross member as a patching optimization model. Based on the finite element stress calculations, we relieve the stress of cross member by patching in two ways-nonuniform thickness patching and optimized uniform thickness patching, the latter of which is more effective in a practical point of view for the preset amount of stress relaxation. Selecting a box type subframe as another finite element analysis model, we then determine the thickness of each part by axiomatic design approach for a preset amount of stress relaxation. The patching methodology and the axiomatic approach adopted in this work can be applied to the other complex shell structures such as center member and lower control arm.

Failure assessment of RPV nozzle under loss of coolant accident

In case of a postulated loss of coolant accident (LOCA) of a reactor pressure vessel (RPV), the nozzle region experiences higher stresses and lower temperatures than the remaining part of the RPV. Thus, the nozzle is to be considered in the RPV safety assessment. For a LOCA event, three-dimensional elastic–plastic finite element calculations of stresses and strains in the intact RPV were performed. Using the substructure technique, fracture mechanics analyses were then carried out for several postulated cracks in the nozzle corner and in the circumferential weld below the nozzle. For different crack geometries and locations, the J-integral and the stress intensity factor were calculated as functions of the crack tip temperature. Based on the K I C -reference curve and the J R curve, both brittle and ductile instability of the postulated cracks were excluded. In order to reduce the expenses of three-dimensional finite element analyses for various crack geometries, an analytical procedure for calculating stress intensity factors of subclad cracks in cylindrical components was extended for cracks in the nozzle corner.

Stresses and strains in epilayers, stripes and quantum structures of III - V compound semiconductors

Stresses and strains in heterostructures have dominated semiconductor research during the last ten years. We review the theory and experimental work on stresses in III - V semiconductor heterostructures in this paper. First large-area lattice mismatched layers (InGaAs and InGaP layers grown on GaAs or InP substrates) and thermally strained layers (GaAs, GaP and InP layers grown directly on Si) are considered. The stresses in large-area epilayer - substrate structures are easy to model because substrate distortion can be neglected and strain in the epilayer is a simple biaxial tetragonal distortion. Calculated splitting of band edges, modification of bandgaps and shifts of Raman modes show good agreement with experiments. Edges of a stripe relax stress in the stripes and induce stress in the substrate. Since stresses in the stripe and the substrate are coupled, calculation of stresses in stripes and substrates is more involved. Recent finite element (FE) calculations of these stresses are discussed in detail and compared with the approximate analytical models and with luminescence and Raman measurements. FE calculations of stresses in buried quantum wires, stressor-induced quantum wires and quantum dots are also discussed. The results of these calculations are used to determine stability and luminescence of the quantum wires and dots and compared with the experimental results. Finally self-organized quantum dots consisting of islands formed during the 3D growth of InAs layers on GaAs are discussed. A possible explanation of the recent observation that they are formed in vertical columns embedded in GaAs is suggested. .

Edge-induced stress and strain in stripe films and substrates: A two-dimensional finite element calculation

Finite element calculations of stresses and strains in substrates and stripe films of thickness h and width 2l are reported. Both variation of the stress in the vertical direction (away from the interface) in the film and distortion of the substrate are taken into account. The calculations show that both the horizontal and vertical lattice planes are curved in the film as well as in the substrate. If the thickness of the substrate is infinite, the curvature in the substrate is maximum near the interface and decays rapidly with depth. Furthermore, the edges near the top are over-relaxed, i.e., if the film is originally under compression, the stress becomes tensile because the free edge surfaces affect the relaxation. For a film with h/l=1 or greater, the stress is reversed throughout the top layer. The change from compression to tension takes place partly because of the Poisson effect and partly due to the bending of the lattice planes. The approximations made in the existing analytical models were examined and the conditions under which the models describe the stresses in the film or in the substrate were determined to a good approximation. Our finite element calculations agree with the available experimental data. Ours are the only theoretical results with which measured substrate stresses agree qualitatively.

Morphology of glacial striae: Implications for abrasion of glacier beds and fault surfaces

Glacial striae, recently exposed on carbonate bedrock adjacent to Saskatchewan Glacier, Alberta, provide information about the mechanics of abrasion beneath temperate glaciers and along fault surfaces. The striae consist of plowed grooves that vary smoothly in width and depth but are located where similar variations in normal stress between the bed and subglacial rock fragments were unlikely. Finite-element calculations of stresses in bedrock beneath abrading fragments suggest that under constant normal loading, plowing elements with steep leading edges will plow progressively deeper into the bed with sliding, whereas those with more gently inclined leading edges will climb out of their grooves. Results of simple experiments in which limestone slabs were pushed beneath fixed plowing elements indicate a similar dependence on contact geometry. This dependence, together with rotation of fragments during glacier sliding, provides a plausible origin for the three characteristic shapes of striae in the area. Shapes of striae indicate that abrading fragments commonly rotate, affecting depths of plowing and the shear stress supported by abrading debris. An important refinement in models of glacial abrasion would be the incorporation of fragment rotations into estimates of abrasion rates and debris-influenced glacier sliding velocities. Some striae become progressively deeper and wider down-glacier and then end abruptly, similar to some fault striae that have been linked to stick-slip phenomena. They may form as a result of tensile fracture at depth in front of plowing asperities that is not necessarily dependent on stick-slip motion. Other minor structures along faults that are used as shear-sense indicators may result from the same process.