Screening Adhesively Bonded Single-Lap-Joint Testing Results Using Nonlinear Calculation Parameters

Report No. ARL-RP-362
Authors: Robert Jensen; Jonathan Kaufman; Wendy Kosik Chaney; Benjamin Henrie
Date/Pages: March 2012; 8 pages
Abstract: Adhesive needs for Army ground vehicles are driven by high strength and high damage tolerance. These basic materials properties requirements do not coincide with traditional aerospace adhesive demands of high strength and high stiffness, which are derived from linear-elastic stress-strain behavior and very little energy absorption. High damage tolerance requires significant energy absorption and the accompanying nonlinear stress-strain response. Therefore, the simplified approach of defining adhesive bond strength as peak load per unit surface area to screen potential adhesives for ground vehicle use is inadequate. Any potential Army interest in defining adhesive property requirements must take the increased complexity of the nonlinear adhesive response into consideration, but without introducing an overburdensome calculation process into the standardization scheme. The single-lap-joint load-displacement behavior for promising ground vehicle adhesives could be captured using Marquardt's nonlinear least-squares regression, but the level of difficulty would be beyond the scope of a simple screening process. Therefore, in this research we propose to use a polynomial regression fit and subsequent first and second derivatives of the load-displacement curves to measure key loads and displacements consistently across a wide range of experimental single-lap-joint test results. The polynomial regression analysis is intentionally designed to perform under the constraints of a common spreadsheet program, thus eliminating the need for specialized software if this proposed analysis scheme yields robust and meaningful data insight for implementation into an Army-derived single-lap-joint adhesive standard.
Distribution: Approved for public release
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Last Update / Reviewed: March 1, 2012