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Research Papers

Investigation of Workpiece Distortion During the Photopolymerization of a PAAW Joint

[+] Author and Article Information
Kristopher R. Doll

Department of Industrial and
Manufacturing Engineering,
The Pennsylvania State University,
University Park, PA 16803

Edward C. De Meter

Department of Industrial and
Manufacturing Engineering,
The Pennsylvania State University,
University Park, PA 16803
e-mail: ecd3@psu.edu

1Corresponding author.

Manuscript received October 21, 2015; final manuscript received April 22, 2016; published online June 23, 2016. Assoc. Editor: Donggang Yao.

J. Manuf. Sci. Eng 138(11), 111008 (Jun 23, 2016) (7 pages) Paper No: MANU-15-1524; doi: 10.1115/1.4033527 History: Received October 21, 2015; Revised April 22, 2016

As a workpiece is bonded to a photo-activated adhesive workholding (PAAW) fixture, the adhesive shrinks during photopolymerization. This leads to the buildup of residual stresses that may distort the workpiece or reduce the external load capacity of the adhesive joints. This research quantifies the impact of adhesive shrinkage on fractional thickness reduction and residual tensile force for a commercially available adhesive and gripper. These variables are quantified for typical ranges of adhesive joint thickness and workpiece interface stiffness. Empirical models are presented for relating these variables. This research reveals that once photopolymerization ceases, workpiece distortion and residual stresses are permanent, and are not diminished by adhesive stress relaxation. It also reveals that the fractional thickness reduction of a PAAW joint can range from close to zero to a value equivalent to the fractional volumetric shrinkage of the adhesive. Furthermore, it decreases with increasing workpiece interface stiffness and increasing adhesive joint thickness following a power law relationship. It is believed that necking within the adhesive joint has a significant influence on this relationship. For stiff workpiece interfaces, residual tensile forces can grow larger than 25% of the tensile break strength of an adhesive joint formed without restraint.

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Figures

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Fig. 2

Adhesive shrinkage test apparatus in doubly supported beam configuration: (a) Blue Photon model 250 HO gripper, (b) view of all major components, and (c) close-up view of adhesive joint prior to curing

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Fig. 1

Adhesive shrinkage phenomena investigated

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Fig. 3

Tensile test coupons: (a) disassembled and (b) assembled

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Fig. 4

Anvil displacement during adhesive polymerization and subsequent cool down; data derived using an anvil displacement stiffness of 15.22 N/μm: (a) adhesive joint thickness = 0.50 mm and (b) adhesive joint thickness = 2.00 mm

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Fig. 5

Anvil displacement after adhesive polymerization and cool down period; data derived using an adhesive joint thickness of 1.00 mm: (a) anvil displacement stiffness = 0.01 N/μm and (b) anvil displacement stiffness = 56.57 N/μm

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Fig. 6

Fractional thickness reduction as a function of anvil displacement stiffness and initial joint thickness

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Fig. 7

Necking of a 1.50 mm thick adhesive joint due to viscous radial flow during photopolymerization: (a) before curing and (b) after curing

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Fig. 8

Residual tensile force versus fractional thickness reduction

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Fig. 9

Tensile break strength of adhesive joints polymerized without residual tensile force

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