Optimal Cooling of Cross-Ply Composite Laminates and Adhesive Joints

1982 ◽  
Vol 49 (4) ◽  
pp. 735-739 ◽  
Author(s):  
Y. Weitsman ◽  
B. D. Harper
Keyword(s):  
Thermal Expansion ◽  
Residual Stresses ◽  
Temperature Dependence ◽  
Composite Laminates ◽  
Thermal Stresses ◽  
Viscoelastic Behavior ◽  
Adhesive Joints ◽  
Analytical Scheme ◽  
Polymeric Resins

This paper concerns the optimal cooling of symmetric, balanced, cross-ply composite laminates and adhesive joints so as to minimize the residual thermal stresses upon termination of the cool-down process. The computations are based on a recently developed analytical scheme and employ up-to-date data on graphite/epoxy laminas. The calculations consider the thermoviscoelastic response of the polymeric resins and incorporate the temperature dependence of the coefficients of thermal expansion. It is shown that the viscoelastic behavior may contribute to a significant reduction of the residual stresses.

Stress Relaxation on Polished Cross-Sections of Al2O3/ZrO2 FGM Discs Measured by Raman Spectroscopy

2005 ◽  
Vol 492-493 ◽  
pp. 641-646 ◽  
Author(s):  
Guy Anné ◽  
Kim Vanmeensel ◽  
Jef Vleugels ◽  
Omer Van der Biest
Keyword(s):  
Experimental Data ◽  
Raman Spectroscopy ◽  
Thermal Expansion ◽  
Stress Relaxation ◽  
Residual Stresses ◽  
Cross Sections ◽  
Thermal Stresses ◽  
Thermal Expansion Mismatch ◽  
Local Composition ◽  
Zirconia Phase

The residual stresses were measured on polished cross-sectioned Al2O3/ZrO2 FGM discs by means of Raman spectroscopy. The experiments revealed that it is possible to measure the residual stresses caused by the thermal expansion mismatch between the alumina and zirconia phase as a function of the position in the FGM. These experimental data are in excellent agreement with the thermal stresses calculated from the local composition using the model of Taya. However, the stresses due to the generated FGM profile could not be measured by means of Raman spectroscopy, due to stress relaxation upon cross sectioning of the FGM disc.

A neutron powder diffraction determination of the thermal expansion tensor of crocoite (PbCrO4) between 60 K and 290 K

1996 ◽  
Vol 60 (403) ◽  
pp. 963-972 ◽  
Author(s):  
Kevin S. Knight
Keyword(s):  
Thermal Expansion ◽  
Temperature Dependence ◽  
Powder Diffraction ◽  
Maximum Expansion ◽  
Lattice Constants ◽  
Thermal Expansion Tensor ◽  
Diffraction Determination ◽  
Line Passing ◽  
Neutron Time

AbstractThe thermal expansion tensor of crocoite has been determined from high-resolution neutron time-of-flight powder diffraction data. The temperature dependence of the lattice constants between 4.5 K and 290 K have been fitted to a quasi-harmonic Einstein model, and the temperature dependence of the thermal expansion tensor has been calculated for 60 K ≤ T ≤ 290 K. The magnitudes of the principal expansivities and their orientation exhibit saturation behaviour for temperatures above 300 K. The predicted saturated expansion coefficients are α11 = 33.1(1) × 10−6K−1, α22 = 15.72(3) × 10−6K−1, α33 = 3.36(1) × 10−6K−1, with α22 parallel to b and α11 lying at an angle of −37.86(5)° to c for the P21/n setting of the crystal structure. The direction of maximum expansion is approximately parallel to both and the least-squares line passing through the projection of the chromium atoms on (010). The direction of minimum expansion lies approximately parallel to [101]. No evidence was found for either a structural or magnetic phase transition between 4.5 K and 300 K.

Phonon Decay in GaN and AlN and Self-Heating in III-N Devices

2006 ◽  
Vol 955 ◽  
Author(s):  
Mark Holtz ◽  
D. Y. Song ◽  
S. A. Nikishin ◽  
V. Soukhoveev ◽  
A. Usikov ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Temperature Dependence ◽  
High Quality ◽  
Self Heating ◽  
Phonon Emission ◽  
Decay Properties ◽  
Phonon Properties

ABSTRACTWe report studies of the temperature dependence of Raman lines in high quality GaN and AlN. The temperature dependence of the phonon energies and linewidths are used to produce consistent phonon decay properties of zone center optic phonons. In GaN we observe the E22 phonon to decay into three phonons, while the A1(LO) phonon is well described according to the so-called Ridley process – one TO and one LA phonon. For AlN the E22 phonon decays by two phonon emission and the A1(LO) line also exhibits a dependence consistent with the Ridley process. Along with the phonon decay processes, it is important in each case to take into account the contribution of the thermal expansion, including the temperature dependence, to describe observed temperature shifts in the phonon properties.

scholarly journals An Improved Analytical Solution for Process-Induced Residual Stresses and Deformations in Flat Composite Laminates Considering Thermo-Viscoelastic Effects

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2506 ◽  
Author(s):  
Chao Liu ◽  
Yaoyao Shi
Keyword(s):  
Differential Equation ◽  
Finite Element ◽  
Analytical Solution ◽  
Residual Stresses ◽  
Composite Laminates ◽  
Composite Structures ◽  
Numerical Models ◽  
Element Analysis ◽  
Current Time ◽  
Viscoelastic Effects

Dimensional control can be a major concern in the processing of composite structures. Compared to numerical models based on finite element methods, the analytical method can provide a faster prediction of process-induced residual stresses and deformations with a certain level of accuracy. It can explain the underlying mechanisms. In this paper, an improved analytical solution is proposed to consider thermo-viscoelastic effects on residual stresses and deformations of flat composite laminates during curing. First, an incremental differential equation is derived to describe the viscoelastic behavior of composite materials during curing. Afterward, the analytical solution is developed to solve the differential equation by assuming the solution at the current time, which is a linear combination of the corresponding Laplace equation solutions of all time. Moreover, the analytical solution is extended to investigate cure behavior of multilayer composite laminates during manufacturing. Good agreement between the analytical solution results and the experimental and finite element analysis (FEA) results validates the accuracy and effectiveness of the proposed method. Furthermore, the mechanism generating residual stresses and deformations for unsymmetrical composite laminates is investigated based on the proposed analytical solution.

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