scholarly journals Hot Tearing in Steels During Solidification: Experimental Characterization and Thermomechanical Modeling

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Cerri Olivier ◽  
Chastel Yvan ◽  
Bellet Michel
Keyword(s):  
Finite Element ◽  
Tensile Stress ◽  
Element Model ◽  
Hot Tearing ◽  
Experimental Characterization ◽  
High Fraction ◽  
Thermomechanical Modeling ◽  
Major Defect ◽  
Do So ◽  
Cast Products

Hot tearing is a major defect in castings or semifinished cast products. It corresponds to the opening of cracks in the mushy zone and, more precisely, in the areas with high fraction of solid (typically 0.9 and beyond) when the material is subjected to deformations leading to local tensile stress. Various kinds of criteria have been developed to highlight a risk of formation of hot tears. The aim of this study is to evaluate their capability to predict the occurrence of hot tears correctly. In order to do so, two kinds of tests have been analyzed with the use of a thermomechanical finite element model.

Numerical analyses on mechanical performance of flat buried approach slab and soil deformation

2021 ◽  
Author(s):  
Junqing Xue ◽  
Dong Xu ◽  
Yufeng Tang ◽  
Bruno Briseghella ◽  
Fuyun Huang ◽  
...  
Keyword(s):  
Finite Element ◽  
Tensile Stress ◽  
Parametric Analysis ◽  
Mechanical Performance ◽  
Element Model ◽  
Soil Deformation ◽  
Longitudinal Deformation ◽  
Expansion Joints ◽  
Approach Slab ◽  
Jointless Bridges

<p><br clear="none"/></p><p>The vulnerability problem of expansion joints could be fundamentally resolved using the concept of jointless bridges. The longitudinal deformation of the superstructure can be transferred to the backfill by using the approach slab. The flat buried approach slab (FBAS) has been used in many jointless bridges in European countries. In order to understand the mechanical performance of FBAS and soil deformation, a finite element model (FEM) was implemented in PLAXIS. Considering the friction between the FBAS and soil, the buried depth, the FBAS length and thickness as parameters, a parametric analysis was carried out. According to the obtained results and in order to reduce the soil deformation above the FBAS, it is suggested to increase the friction between the FBAS and sandy soil, and the buried depth of FBAS. Moreover, it should be paid attention to the vertical soil deformation and the concrete tensile stress of FBAS in pulling condition.</p>

Maximum Stress at Intersecting Bores of Pressurized Blocks

1994 ◽  
Author(s):  
Ajay Garg
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Tensile Stress ◽  
Element Model ◽  
Maximum Tensile Stress ◽  
Pressure Vessels ◽  
Experimental Results ◽  
Empirical Methods ◽  
Element Analysis ◽  
Matched Design

Abstract In high pressure applications, rectangular blocks of steel are used instead of cylinders as pressure vessels. Bores are drilled in these blocks for fluid flow. Intersecting bores with axes normal to each other and of almost equal diameters, produce stresses which can be many times higher than the internal pressure. Experimental results for the magnitude of maximum tensile stress along the intersection contour were available. A parametric finite element model simulated the experimental set up, followed by correlation between finite element analysis and experimental results. Finally, empirical methods are applied to generate models for the maximum tensile stress σ11 at cross bores of open and close ended blocks. Results from finite element analysis and empirical methods are further matched. Design optimization of cross bores is discussed.

scholarly journals Research on Mechanical Response of Pavement Structure to Differential Settlement of Subgrade on Highway Widening

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Quanjun Shen ◽  
Yu Lu ◽  
Yaohui Yang ◽  
Guanxu Long
Keyword(s):  
Finite Element ◽  
Tensile Stress ◽  
Mechanical Response ◽  
Element Model ◽  
Differential Settlement ◽  
Failure Strength ◽  
Pavement Surface ◽  
Practical Engineering ◽  
Pavement Structure ◽  
The Finite Element Model

Based on the widening project of Ri-Lan highway in China, the finite element model is established by PLAXIS. By applying differential settlement at the bottom of the pavement, the mechanical response of the pavement structure is analysed. Finally, the differential settlement control standard indicated by crack strength is proposed. The results show that, under the effect of differential settlement, within about 4 cm of old pavement surface and upper base bear tensile stress, the base first reaches the failure strength. Under 4 cm of the old pavement surface, the subbase first reaches the failure strength. The differential settlement control standard of the pavement structure is determined by the splitting strength of the material, and we, respectively, control the differential settlement of less than 23.4 mm, where the corresponding cross-slope rate is 0.33%, and below 75.2 mm, where the corresponding cross-slope rate is 0.54%. It could support practical engineering applications.

Stress Analysis of a Novel MEMS Microphone Chip Using Finite Element Analysis

2005 ◽  
Author(s):  
Jia Gao ◽  
Ronald N. Miles ◽  
Weili Cui
Keyword(s):  
Finite Element ◽  
Low Temperature ◽  
Tensile Stress ◽  
Finite Element Model ◽  
Oxide Layer ◽  
Compressive Stress ◽  
Failure Modes ◽  
Element Model ◽  
Mems Devices ◽  
Mems Microphone

Residual stress produces major challenges in the fabrication of MEMS devices. This is particularly true in the development of MEMS microphones since the response of the thin sound-sensitive diaphragm is strongly affected by stress. It is important to predict the effects of fabrication stress on the microphone chip and identify the failure modes to ensure a satisfactory fabrication yield. In this study, a finite element model of the microphone chip is developed to analyze the laminated structure under different fabrication stresses. The model of the microphone chip includes the diaphragm, backplate and sacrificial oxide layers on top of the silicon substrate. Fabrication stresses are included through the use of an equivalent thermal stress. The stresses in the different layers have been estimated based on measurements performed on fabricated test structures. The estimated stresses are simulated in the finite element model. An important factor in determining the process reliability is the compressive stress of the low temperature sacrificial oxide layer (LTO). A variety of stress combinations between different layers with the low temperature oxide layer are investigated. It is found that an adequate level of tensile stress in the backplate is crucial to ensure the fabrication yield. In the designs considered here, silicon nitride in combination with a thin conductive layer is identified as a favorable material for the backplate considering its high modulus and tensile stress in ‘as deposited’ film. In addition, the presence of a LTO layer on the backside of the wafer turns out to be very helpful in reducing the deflection of the unreleased chip and the stress in the diaphragm. In the case where there is a net compressive stress in the laminate, the failure mode is identified by nonlinear analysis. This analysis provides a guideline to select robust materials and tune the fabrication process to ensure a satisfactory fabrication yield.

scholarly journals Experimental Characterization and Finite Element Modeling of the Effects of 3D Bioplotting Process Parameters on Structural and Tensile Properties of Polycaprolactone (PCL) Scaffolds

2020 ◽  
Vol 10 (15) ◽  
pp. 5289
Author(s):  
Lokesh Karthik Narayanan ◽  
Rohan A. Shirwaiker
Keyword(s):  
Finite Element ◽  
Tensile Properties ◽  
Element Model ◽  
Extrusion Pressure ◽  
Fibroblast Cells ◽  
Experimental Characterization ◽  
Efficient Design ◽  
Strand Spacing ◽  
Nih 3T3 ◽  
Process Structure

In this study we characterized the process–structure interactions in melt extrusion-based 3D bioplotting of polycaprolactone (PCL) and developed predictive models to enable the efficient design and processing of scaffolds for tissue engineering applications. First, the effects of pneumatic extrusion pressure (0.3, 0.4, 0.5, 0.6 N/mm2), nozzle speed (0.1, 0.4, 1.0, 1.4 mm/s), strand lay orientation (0°, 45°, 90°, 135°), and strand length (10, 20, 30 mm) on the strand width were investigated and a regression model was developed to map strand width to the two significant parameters (extrusion pressure and nozzle speed; p < 0.05). Then, proliferation of NIH/3T3 fibroblast cells in scaffolds with two different stand widths fabricated with different combinations of the two significant parameters was assessed over 7 days, which showed that the strand width had a significant effect on proliferation (p < 0.05). The effect of strand lay orientation (0° and 90°) on tensile properties of non-porous PCL specimens was determined and was found to be significantly higher for specimens with 0° lay orientation (p < 0.05). Finally, these data were used to develop and experimentally validate a finite element model for a porous PCL specimen with 1:1 ratio of inter-strand spacing to strand width.

Study on Bending and Upsetting Forging 305 Marine Crankshaft

2010 ◽  
Vol 97-101 ◽  
pp. 337-343 ◽  
Author(s):  
Miao Jin ◽  
Shi Yan Zhao ◽  
Bao Feng Guo ◽  
Qun Li
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Optimal Combination ◽  
Experimental Results ◽  
Rigid Plastic ◽  
Forming Quality ◽  
Root Cause ◽  
Major Defect

Roll-over of crank arm is the major defect of forming quality during the upsetting process. Bending and upsetting forging of crankshaft was simulated by using the rigid-plastic finite element model. The theories of metal flowing and distribution of deformation during the bending and upsetting forging were analyzed, the root cause of the roll-over of crank was found; the optimal combination of the bending and upsetting velocities was obtained; the experimental results agree well with simulations.

scholarly journals Analysis of the Static Behavior of a Single Tree on a Finite Element Model

Plants ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1284
Author(s):  
Ľuboš Moravčík ◽  
Radko Vincúr ◽  
Zdenka Rózová
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Structural Analysis ◽  
Tensile Stress ◽  
Finite Element Model ◽  
Cross Section ◽  
Element Model ◽  
Tree Structure ◽  
Element Analysis ◽  
Whole Tree

This work deals with the innovated complex process of tree risk assessment, from precise geometrical tree shape acquisition to building and analyzing a finite element model under specified load. The acquisition of the 3D geometry of the tree was performed by means of terrestrial laser scanning. Obtained point cloud was optimized and additionally converted to a 3D CAD model, representing the bearing skeleton compound of trunk and main branches. For structural analysis purposes, a finite element model (FEM) was built in the form of beam structure fixed to the ground. Particular beams were defined by geometry, material properties of wood, and cross sections. An acoustic tomography was applied for determination of the precise cross section on investigated locations of an analysis model. Finite element analysis performed on the computational model shows the bearing capacity and deformations of the whole tree structure caused by combinations of load cases like self-weight and static equivalent of wind load. The results of the structural analysis called attention to potentially dangerous places within the tree structure with extreme node displacements or tensile stresses on beams. Thus, we observed a maximal horizontal displacement of 280.4 mm in node N34 and dangerous tensile stress in node N26, where it reaches +23.6 MPa. After filtering some beams with an abnormal cross section geometry, the finite element analysis of the whole tree structure showed the highest tensile stress of +8.8 MPa and highest compressive stress of −8.9 MPa. The suggested method can be applied generally for the prediction of potentially risky tree suspected of breakage and especially for monumental trees, where the presented method can be mostly applicable.

Experimental Characterization and Modelling Validation of Shape Memory Alloy Negator Springs

2013 ◽  
Author(s):  
Andrea Spaggiari ◽  
Eugenio Dragoni ◽  
Ausonio Tuissi
Keyword(s):  
Finite Element ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Analytical Model ◽  
Element Model ◽  
Design Tool ◽  
Experimental Characterization ◽  
Finite Element Software ◽  
Spiral Spring ◽  
Force Displacement

This paper is aimed at the experimental characterization and modelling validation of shape memory alloy (SMA) negator springs. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The main feature of a Negator springs is the nearly-constant force displacement behaviour in the unwinding of the strip. Moreover the stroke is very long, theoretically infinite as it depends only on the length of the initial strip. A Negator spring made in SMA is built and experimentally tested to demonstrate the feasibility of this actuator. The shape memory Negator spring behaviour is predicted both with an analytical model and with a a finite element software. In both cases the material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The experimental results confirms the applicability of this kind of geometry to the shape memory alloy actuators and the analytical model is confirmed to be a powerful design tool to dimension and predict the spring behaviour both in martensitic and austenitic range, as well as the finite element model developed.

Monolithic Roadbed's Mechanical Behavior Affected by Structural Thickness under Tram

2013 ◽  
Vol 361-363 ◽  
pp. 1664-1670
Author(s):  
Chong Wei Huang ◽  
Er Hao Su ◽  
Xian Zhi Shao ◽  
Yi Zhang ◽  
Lie Ping Wang
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Tensile Stress ◽  
Mechanical Behavior ◽  
Compressive Stress ◽  
Contact Problems ◽  
Element Model ◽  
Nonlinear Contact ◽  
Structure Layer ◽  
Abaqus Software

Based on ABAQUS software, a 3-D finite element model which content the nonlinear contact problems and contact-earth subgrade-monilithic was given to analysis the mechanical behavior of the monolithic roadbed. Mechanics behavior and deflection of the monolithic roadbed, deflection and compressive stress of earth subgrade evaluated in detail with respect to varied structure layer combination and materials parameters. The results indicate that the increase roadbed thickness can significantly reduce the monolithic roadbeds tensile stress, which can reach 1.042MPa. With the increase of the friction coefficient, level of tensile stress σdy, monolithic deflection Dd , the compressive stress σsz and deflection on earth subgrade were slightly reduced.

Finite Element Analysis of Fretting Stresses

1997 ◽  
Vol 119 (4) ◽  
pp. 797-801 ◽  
Author(s):  
P. A. McVeigh ◽  
T. N. Farris
Keyword(s):  
Finite Element ◽  
Tensile Stress ◽  
Element Model ◽  
Fretting Fatigue ◽  
Maximum Tensile Stress ◽  
Multiaxial Fatigue ◽  
Fretting Wear ◽  
Symmetric Distribution ◽  
Element Analysis ◽  
Riveted Joints

Clamped contacts subjected to vibratory loading undergo cyclic relative tangential motion or micro-slip near the edges of contact. This cyclic micro-slip, known as fretting, leads to removal of material through a mechanism known as fretting wear and formation and growth of cracks through a mechanism known as fretting fatigue. In aircraft, fretting fatigue occurs at the rivet/hole interface leading to multisite damage which is a potential failure mechanism for aging aircraft. A finite element model of a current fretting fatigue experiment aimed at characterizing fretting in riveted joints is detailed. A non-symmetric bulk tension is applied to the specimen in addition to the loads transferred from the fretting pad. The model is verified through comparison to the Mindlin solution for a reduced loading configuration, in which the bulk tension is not applied. Results from the model with the bulk tension show that the distribution of micro-slip in the contact is not symmetric and that for some loads reversed micro-slip occurs. Finite element results are given for the effects that four different sets of loading parameters have on the maximum tensile stress induced by fretting at the trailing edge of contact. It can be shown using multiaxial fatigue theory that this stress controls fretting fatigue crack formation. This maximum tensile stress is compared to that of the Mindlin solution for a symmetric distribution of micro-slip. This stress is also compared to that of a variation based on the Mindlin solution for the cases with a non-symmetric distribution of micro-slip. It is concluded that the solution based on the Mindlin variation and the full finite element solution lead to similar predictions of the maximum tensile stress, even when the shear traction solutions differ significantly.

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