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Research Papers

Failure Analysis of Composite-Based Lightweight Multimaterial Joints in Tensile-Shear Tests After Cyclic Heat at High-Relative Humidity

[+] Author and Article Information
Kaori Sakai

Department of Mechanical Engineering,
Fastening and Joining Research Institute (FAJRI),
Oakland University,
Rochester, MI 48309
e-mail: ksakai@oakland.edu

Sayed A. Nassar

Fellow ASME
Department of Mechanical Engineering,
Fastening and Joining Research Institute (FAJRI),
Oakland University,
Rochester, MI 48309
e-mail: Nassar@oakland.edu

Manuscript received October 31, 2015; final manuscript received July 25, 2016; published online October 19, 2016. Assoc. Editor: Wayne Cai.

J. Manuf. Sci. Eng 139(4), 041007 (Oct 19, 2016) (9 pages) Paper No: MANU-15-1543; doi: 10.1115/1.4034888 History: Received October 31, 2015; Revised July 25, 2016

Failure analysis of tensile-shear tested bonded composite-based single lap joints (SLJs) that have been subjected to two different levels of cyclic environmental loading is provided. Each test joint has at least one composite adherend which is made of glass fiber-reinforced polymer (GFRP); the second adherend may be aluminum, magnesium, or GFRP composite, and structural epoxy adhesive is used to join two adherends together for creating test joints. Scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) are utilized to investigate the root cause failure of fractured surfaces that gives an insight into the recently published data that showed a significant effect of the cyclic heat on the static load transfer capacity (LTC) of the same SLJs. The SEM and EDS inspections show that the failure mode shifts from interfacial adhesive failure (ADH) to fiber tear (FT) for the GFRP/GFRP joints that have been exposed to cyclic heat with and without high relative humidity as compared to that at ambient condition. Further, failure analysis and discussion are provided.

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Figures

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Fig. 4

Schematic of tensile shear test set up

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Fig. 3

Cyclic temperature and constant relative humidity profiles: (a) environmental condition 2 and (b) environmental condition 3

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Fig. 8

FEA peel stress on bond line versus axial location: GFRP/GFRP joint

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Fig. 5

Photographed images of fractured surfaces following the LTC testing with each environmental effect

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Fig. 6

Selected SEM images of fractured surfaces following the LTC testing with each environmental effect for (a) baseline and (b) cyclic heat only, and (c) cyclic heat and RH 85% effect

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Fig. 7

Sample EDS spectra measured at selected area of fractured surfaces following LTC testing for: (a) baseline and (b) cyclic heat and RH 85% effect

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Fig. 9

FEA peel stress on bond line versus axial location: GFRP/magnesium joint

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Fig. 10

FEA peel stress on bond line versus axial location: GFRP/aluminum joint

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Fig. 11

FEA shear stress on bond line versus axial location: GFRP/GFRP joint

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Fig. 12

FEA shear stress on bond line versus axial location: GFRP/magnesium joint

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Fig. 13

FEA shear stress on bond line versus axial location: GFRP/aluminum joint

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Fig. 2

Two-dimensional profiles of adherend surface: (a) surface of GFRP adherend, (b) surface of magnesium adherend, and (c) surface of aluminum adherend

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Fig. 1

Schematic of a test SLJ

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