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Research Papers

Effect of Residual Shear Stresses on Released Strains in Isotopic and Orthotropic Materials Measured by the Slitting Method

[+] Author and Article Information
Mahmood M. Shokrieh

Composites Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering,  Iran University of Science and Technology, Tehran 16846-13114, IranShokrieh@iust.ac.ir

Saeed Akbari R.

Composites Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering,  Iran University of Science and Technology, Tehran 16846-13114, Iran

J. Eng. Mater. Technol 134(1), 011006 (Dec 06, 2011) (9 pages) doi:10.1115/1.4005267 History: Received May 30, 2011; Accepted September 15, 2011; Revised September 15, 2011; Published December 06, 2011; Online December 06, 2011

This paper investigates the effect of shear stresses on the determination of residual stresses in isotropic and orthotropic materials by the slitting method. A great deal of research effort is focused on the estimation of the residual stress component normal to the slit face using strain data measured by strain gauges installed on the top or the back surface of the stressed specimens. However, the slitting process will also release two in-plane and out-of-plane shear stress components, which may influence the measured strains. For the two specimens of carbon/epoxy and glass/epoxy laminated composites as well as a steel specimen, the distribution of released strains on the top and the back surfaces due to the shear stresses is calculated using finite element method and compared with those due to the residual normal stress. The results show that on the back surface, the shear stresses have a very small effect on the measured strains. However, on the top surface, strains due to the residual shear stresses are significant compared with those due to the residual normal stress and cannot be ignored. A method using two top surface strain gauges in both sides of the slit is presented to separate the effects of normal and shear stresses from each other. Also, strains due to the in-plane and the out-of-plane shear stresses could be isolated from each other. If these separations could be carried out successfully, the residual shear stress can be calculated by the proposed formulation.

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Figures

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Figure 1

A typical configuration of slitting method with back surface strain gauge [22]

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Figure 2

Side view of a real specimen with cantilever boundary condition

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Figure 3

Top view of three-dimensional finite element mesh

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Figure 4

Coordinate system considered for stress distributions

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Figure 5

Distribution of released strain on back surface for a glass/epoxy [±45]s laminate due to (a) residual normal stress: σyy  = 10(6x2  − 6x + 1) MPa (b) residual out-of-plane shear stress: τyx  = 10 sin(2πx) MPa (c) residual in-plane shear stress: τyz  = 10 sin (2πz/3) MPa

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Figure 6

Distribution of released strain on back surface for a steel specimen due to (a) residual normal stress: σyy  = 10(6x2 6x + 1) MPa (b) residual out-of-plane shear stress: τyx  = 10 sin(2πx) MPa (c) residual in-plane shear stress: τyz  = 10 sin(2πz/3) MPa

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Figure 7

Distribution of released strain on top surface for a carbon/epoxy [0/±45/90]s laminate due to (a) residual normal stress: σyy  = 10(6x2 6x + 1) MPa (b) residual out-of-plane shear stress: τyx  = 10 sin(2πx) MPa (c) residual in-plane shear stress: τyz  = 10 sin(2πz/3) MPa

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Figure 8

Distribution of released strain on top surface for a glass/epoxy [±45]s laminate due to (a) residual normal stress: σyy  = 10(6x2  − 6x + 1) MPa (b) residual out-of-plane shear stress: τyx  = 10 sin(2πx) MPa (c) residual in-plane shear stress: τyz  = 10 sin(2πz/3) MPa

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Figure 9

Distribution of released strain on top surface for a steel specimen due to (a) residual normal residual normal stress: σyy  = 10(6x2  − 6x + 1) MPa (b) residual out-of-plane shear stress: τyx  = 10 sin(2πx) MPa (c) residual in-plane shear stress: τyz  = 10 sin(2πz/3) MPa

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Figure 10

(a) Residual normal stress (b) residual shear stresses acting on the plane of the slit

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Figure 11

Both normal and shear stresses exist in the plane of slit

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Figure 12

Released normal strain (μɛ) due to residual out-of-plane shear stress (τyx  = 10 sin(2πx) MPa) for a steel specimen (slit depth: a = 0.6) in (a) z′-direction b) y′-direction

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Figure 13

Released normal strain (μɛ) due to residual in-plane shear stress (τyz  = 10 sin(2πz/3) MPa) for a steel specimen (slit depth: a = 0.6) in a) z′-direction b) y′-direction

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