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Research Papers

Estimation of Residual Stresses in Laminated Composites by Slitting Method Utilizing Eigen Strains

[+] Author and Article Information
M. M. Shokrieh

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

M. A. Kamangar

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

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 14, 2015; final manuscript received April 4, 2016; published online June 13, 2016. Assoc. Editor: Erdogan Madenci.

J. Eng. Mater. Technol 138(4), 041003 (Jun 13, 2016) (8 pages) Paper No: MATS-15-1254; doi: 10.1115/1.4033374 History: Received October 14, 2015; Revised April 04, 2016

The manufacturing parameters such as curing process cause residual stresses in polymeric laminated composites. Therefore, an accurate method of measurement of residual stresses is essential for the design and analysis of composites structures. The slitting method is recently used for measurement of the residual stresses in laminated composites. However, this method has some drawbacks such as high sensitivity to noise of measurements and high scattering in the final results, which necessitate using of normalization techniques. Moreover, the form of polynomials, used in the conventional slitting method for calculation of the stiffness matrix, has a significant effect on final results. In this paper, it is shown that the major reason of the drawbacks of the slitting method in calculating the residual stresses is a direct use of the elastic released strains recorded by strain gages. In the present study, instead of direct calculation of residual stresses from the elastic released strains, eigen strain distribution as a constant and invariant field has been calculated from the recorded elastic strains. Then, by using the calculated eigen strain field in a finite-element model, the residual stress filed was obtained. Also, instead of using polynomials to calculate the compliance, a superposition method was used. The results show that the new method decreases the sensitivity of the final results to noise and scattering of the experimental data. It means that the normalization methods are not needed any more.

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References

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Figures

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Fig. 1

A schematic figure of slitting method

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Fig. 2

Effect of number of terms in a polynomial on the condition number [9]

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Fig. 3

The coordinate system

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Fig. 4

Finite-element model of a five-layer laminate model

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Fig. 5

The groups of nodes

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Fig. 6

A comparison of stresses calculated by the model and the FEM

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Fig. 7

Effect of singularity of matrix M on results

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Fig. 8

The customary emplacement of strain gages in slitting method

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Fig. 9

The front and back surfaces view of the model (left and right)

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Fig. 10

Comparison of the induced and calculated eigen strains

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Fig. 11

Ratio of recorded elastic strain for different slot width

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Fig. 12

A view of 16-layer model

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Fig. 13

The deviation of estimated results from the exact results

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Fig. 14

Laminated composite samples

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Fig. 15

The recorded strain during the slitting

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Fig. 16

A comparison between the results obtained by the MSS and conventional methods

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