Experimental Characterization of the Bearing Strength of Fiber Metal Laminates

Abstract

A novel experimental methodology extended from ASTM D953 was developed and implemented to conduct pin bearing experiments on GLARE3-5/4-0.3 and GLARE3-4/3-0.3 variants with the aim to examine a bearing load configuration from a local perspective as well as a global one. This was accomplished by introducing previously unconsidered testing fixtures and additional instrumentation, including bonded strain gages, as a means of measuring the local strain field generated by a bearing load. Load—displacement curves were produced as per the standard but were subject to numerous plateaus and significant statistical scatter, attributed to pin seating and global displacement measurement. Conventionally defined bearing yield strengths were calculated but lacked physical meaning, prompting the production of novel bearing strength vs. measured strain profiles. These new profiles, derived from the additionally acquired data, were void of the plateau anomalies and depicted a well defined trend, indicative of a more complete characterization of material response. Examination of these profiles resulted in a new, more intuitive definition of bearing yield strength that incorporated influence from the entire curve rather than idealizing it bilinearly. The phenomenological basis of the new definition suggests an analogous extension to additional methodologies such as standard tensile or compressive tests.

On the Pin Bearing Behavior of Orthotropic Fiber Metal Laminates

“…These results agree exceptionally well with the material constitutive responses reported in Ref. [17] and demonstrates the robustness of a locally applied, strain measurement scheme.…”

“…In addition, the parameters a and b are empirical values determined The effective domains featured in the piecewise approximation were selected such that the linear approximations were nearly tangent to the endpoints of the logarithmic approximation's domain. The resulting ranges over which each specific portion of the piecewise function acts differed only marginally from specimen to specimen and never more than 10%, analogous to the previous application of the novel protocol, though slightly modified [17]. Figure 9 depicts a direct application of the piecewise approximation on a typical GLARE 4 specimen subject to a pin bearing load.…”

“…Since it has been previously reported in the literature [10][11][12]16,17] that a pin bearing load configuration is the most conservative means for simulating a mechanically fastened joint by virtue of its encouragement of delamination and buckling, it is merely prudent to examine the local stress-strain behavior of an orthotropic variant of GLARE in this light as well [18]. The hardened side plates employ a 4.8 mm diameter loading pin for easier application to practical joint design and the assurance of geometric congruency to previous FE studies [16], to which the present research is related to.…”

“…[17] was also employed herein. The material's response to the bearing load can be characterized through the regression of two linear approximations -corresponding to the low and high strain regimes -and a single natural logarithmic approximation of the non-linear bridge, resulting in a piecewise function acting over intervals as shown in Equation (2)…”

“…Most recently, Krimbalis et al [17] developed a novel experimental protocol for the measurement and extraction of a newly defined bearing yield strength value, based on the predictions in Ref. [16] and performed, in a pin bearing fashion, on the quasi-isotropic GLARE 3 variant.…”