Journal of Applied Polymer Science,Vol. 139, Issue 6, 2022, 51620, DOI: 10.1002/app.51620

Measurement of Effective Cure Shrinkage of Epoxy-based Molding Compound by Fiber Bragg Grating Sensor using Two-stage Curing Process

Changsu Kim, Sukrut Prashant Phansalkar, Hyun-Seop Lee and Bongtae Han
Mechanical Engineering Department,University of Maryland and College Park,Maryland, USA

For more information about this article and related research, please contact Prof. Bongtae Han


Cure shrinkage accumulated only after the gel point is known as effective cureshrinkage (ECS), which produces residual stresses inside molded components.The ECS of an epoxy-based molding compound (EMC) is measured by anembedded fiber Bragg grating (FBG) sensor. Under a typical molding condi-tion, a high mold pressure inherently produces large friction between EMCand mold inner surfaces, which hinders EMC from contracting freely duringcuring. A two-stage curing process is developed to cope with the problem. Inthe first stage, an FBG sensor is embedded in EMC by a molding process, andthe FBG-EMC assembly is separated from the mold at room temperature. Themolded specimen is heated to a cure temperature rapidly in the second stageusing a constraint-free curing fixture. Several technical issues have to be takeninto considerations to ensure that (1) EMC does not pass the gel point before itreaches the cure temperature, and (2) EMC cures uniformly around the FBGduring measurements. The ECS of an EMC with a filler content of 88 wt% ismeasured by the proposed method, and its value is 0.077%. The repeatability ofthe proposed method is corroborated by the results of a duplicate test.

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