Optimal Cool-Down in Linear Viscoelasticity

1980 ◽  
Vol 47 (1) ◽  
pp. 35-39 ◽  
Author(s):  
Y. Weitsman
Keyword(s):  
Residual Stress ◽  
Optimal Path ◽  
Viscoelastic Plate ◽  
Geometric Constraints ◽  
Optimal Temperature ◽  
Cooling Process ◽  
Linear Viscoelastic ◽  
Stress Free State ◽  
Temperature Path ◽  
Optimal Cool

An optimal temperature path is derived for a thin viscoelastic plate which is cooled from a stress-free state against geometric constraints. The optimal path, which minimizes the final residual stress due to cool down, is shown to possess discontinuities at the initial and final times and to be smooth and continuous during all intermediate times. An iterative convergent scheme is provided for a wide class of linear viscoelastic responses and typical paths are determined for two specific cases. In addition, a time-temperature path which maintains constant stress values during cool-down is derived. The problem is motivated by the cooling process of composite materials.

Optimal Cool Down in Nonlinear Thermoviscoelasticity With Application to Graphite/Peek (APC-2) Laminates

1994 ◽  
Vol 61 (2) ◽  
pp. 367-374 ◽  
Author(s):  
K. Lee ◽  
Y. Weitsman
Keyword(s):  
Composite Laminates ◽  
Thermal Stresses ◽  
Resin Composite ◽  
Strong Dependence ◽  
Temperature Drop ◽  
Geometric Constraints ◽  
Temperature History ◽  
Thermoplastic Resin ◽  
Cooling Process ◽  
Optimal Cool

Many thermoplastic resin composite laminates, such as those made of APC-2, undergo a substantial temperature drop during their post-manufacturing cool down. This thermal excursion induces significant residual thermal stresses into the laminate due to the mutual geometric constraints among the multidirectional plies. In view of the considerable time-dependent relaxation which occurs during the cooling process, the residual thermal stresses exhibit strong dependence on the temperature history. However, in view of the high magnitudes of those stresses, the relaxation behavior is viscoelastically nonlinear. This paper demonstrates that it is possible to obtain an optimal cool-down path which minimizes the residual thermal stresses in APC-2 composites upon the termination of the cooling process.

A Numerical Investigation into Residual Stress Characteristics in Laser Deposited Multiple Layer Waspaloy Parts

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
A. M. Kamara ◽  
S. Marimuthu ◽  
L. Li
Keyword(s):  
Residual Stress ◽  
Structural Integrity ◽  
Service Failures ◽  
Number Of Layers ◽  
Multiple Layer ◽  
Combined Use ◽  
Aerospace Sector ◽  
Finite Element Package ◽  
Stress Free State ◽  
Good Agreement

This paper reports an investigation into the residual stress generated with the laser direct metal deposition (LDMD) process and particularly that which arises from the deposition of a multiple-layer wall of Waspaloy on an Inconel 718 substrate. These Ni-based superalloys possess excellent strength and creep resistance at relatively high temperatures. These are attributes contributing to their extensive utilization in various applications in modern industry and particularly in the aerospace sector. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stress generated in the combined use of these materials in an LDMD process affect interfacial bonding and structural integrity during the process, and it can also cause unpredicted in-service failures. Prediction of its distribution in the deposited structure is vital toward enhancing process optimization that could lead to its control. Using the ANSYS finite element package, this study investigated the residual stress characteristics in a 6 mm wide and 14 mm high Waspaloy wall that was built from the deposition of 20 layers each consisting of 6 parallel tracks. The predicted results were validated by published experimental data and showed very good agreement. The results indicated that irrespective of the position in the height of the wall, the stress along the length of the wall oscillates about a stress-free state. Along the height of the wall, the stress was found to vary with position. The wall is near stress-free close to the substrate, while, at positions close to the free surface, the stress was uniaxially tensile. The largely tensile stress in the beam scanning direction in the deposited wall increases with number of layers while the stress in the build-up direction in the wall is close to zero.

scholarly journals Analytical and Experimental Study of Residual Stresses in CFRP

2013 ◽  
Vol 2013 ◽  
pp. 1-4
Author(s):  
Chia-Chin Chiang ◽  
Vu Van Thuyet ◽  
Shih-Han Wang ◽  
Liren Tsai
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Fiber Reinforced Polymer ◽  
Carbon Fiber Reinforced Polymer ◽  
Curing Process ◽  
Cooling Process ◽  
Element Analysis ◽  
Reinforced Polymer ◽  
Fiber Reinforced Polymer Composites ◽  
Good Environment

Fiber Bragg Grating sensors (FBGs) have been utilized in various engineering and photoelectric fields because of their good environment tolerance. In this research, residual stresses of carbon fiber reinforced polymer composites (CFRP) were studied using both experimental and analytical approach. The FBGs were embedded inside middle layers of CFRP to study the formation of residual stress during curing process. Finite element analysis was performed using ABAQUS software to simulate the CFRP curing process. Both experimental and simulation results showed that the residual stress appeared during cooling process and the residual stresses could be released when the CFRP was machined to a different shape.

Influence of Hot Leveling and Cooling Process on Residual Stresses of Steel Plates

2010 ◽  
Vol 168-170 ◽  
pp. 1130-1135 ◽  
Author(s):  
Ji Ping Chen ◽  
Jian Qing Qian ◽  
Sheng Zhi Li
Keyword(s):  
Residual Stress ◽  
Temperature Distribution ◽  
Residual Stresses ◽  
Initial Temperature ◽  
Steel Plate ◽  
Coupled Model ◽  
Distribution Patterns ◽  
Cooling Process ◽  
Initial Temperature Distribution ◽  
Actual Measurement

A three-dimensional thermo-mechanical coupled model of hot leveling and cooling processes of the steel plate has been conducted with MSC.Superform software. Four kinds of initial temperature distribution patterns have been determined according to literature. The effects of hot leveling and cooling processes on the transversal and longitudinal residual stresses of the steel plate have been analyzed. The results show that the initial temperature distribution patterns have significant influence on the residual stress of the plate. The more uniform temperature distribution patterns along the width of the plate, the smaller residual stress and also the smaller stress fluctuations. The cooling process has greater effect on the residual stress compared with the hot leveling process. The bigger the temperature gradient along the width of steel plate, the larger the residual stress and its fluctuation is. Through the FEM study, the value and direction of transversal and longitudinal residual stresses can be confirmed quantitatively at various positions along the width and length of plate, which can provide guidance to actual measurement of residual stress.

scholarly journals Numerical Simulation and Experimental Investigation of Temperature and Residual Stress Distributions in a Circular Patch Welded Structure

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5423 ◽  
Author(s):  
Mato Perić ◽  
Sandro Nižetić ◽  
Zdenko Tonković ◽  
Ivica Garašić ◽  
Ivan Horvat ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Welding Process ◽  
Infrared Camera ◽  
Circular Disk ◽  
Maximum Deviation ◽  
Cooling Process ◽  
Residual Stress Field ◽  
Circular Patch ◽  
Welded Structure

In this study, we performed a numerical simulation and experimental measurements on a steel circular patch welded structure to investigate the temperature and residual stress field distributions caused by the application of buried-arc welding technology. The temperature histories during the welding and subsequent cooling process were recorded for two locations, with the thermocouples mounted inside the plate close to the weld bead. On the upper surface of the welded model, the temperature-time changes during the cooling process were monitored using an infrared camera. The numerically calculated temperature values correlated well with the experimentally measured ones, while the maximum deviation of the measured and calculated temperatures was within 9%. Based on the numerical result analysis regarding circumferential and radial stresses after the completion of the welding process, it is concluded that both stresses are primarily tensile within the circular disk. Outside the disk, the circumferential stresses turn from tensile to compressive, while on the other hand the radial stresses disappear towards the ends of the plate.

The Research on Thermal Residual Stress of SiCp/Al Composites

2014 ◽  
Vol 852 ◽  
pp. 127-131
Author(s):  
Jin Zou ◽  
Jian Yun Zhang ◽  
De Ping Lu ◽  
Qi Jie Zhai
Keyword(s):  
Residual Stress ◽  
Thermal Residual Stress ◽  
X Ray Diffraction ◽  
Cooling Process ◽  
Time Curve ◽  
Cooling Rates ◽  
Thermal Residual Stresses ◽  
Dimension Stability ◽  
The Difference ◽  
Particle Shapes

SiCp/Al composites would produce a large thermal residual stresses field during cooling process. The thermal residual stress has a greater impact to the composites dimension stability and the accuracy of application. In this paper, the thermal residual stress in SiCp/A356 composites was measured by X-ray diffraction and simulated by finite element method (FEM), the influence of particle shapes and cooling rates are considered, the stress field contour nephogram and stress-time curve during cooling was simulated. The studies present residual stress formed during cooling process because of the difference of thermal expansion coefficient (CTE) between SiC particle and aluminum alloy, the maximum stress distributes near the interface of matrix/SiCp mainly. The stress-time curves are inconsistent under different cooling rates, the higher cooling rate, the more dramatic variety in stress.

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