| Description |
Composite materials have the distinctive ability to tailor a structure's mechanical properties to achieve a desired result. Because of this capability, composite laminates with embedded damping materials have gained interest as a means to improve the damping characteristics of structures. By constraining a layer of damping material near the mid-thickness of the laminate, significant damping may be obtained under flexural loading since the interior of the region experiences the highest shear strains. As the use of embedded damping materials gains interest, however, an understanding of the structural integrity of such composite laminates is needed. This thesis addresses the need for a mechanical test method to assess the structural integrity of composite laminates with embedded damping material. An important aspect of the desired test method is to permit the measurement of in situ properties of the composite laminate so that the effects of manufacturing may be identified. The use of the single lap joint test was explored as a means for determining the in situ shear modulus of the damping material and structural integrity of the composite laminate. Finite element analyses were performed to investigate the effects of the specimen geometry and adherend material on the stress state in the single lap joint specimen. Three candidate strain measurement methodologies were assessed for determining the in situ shear modulus of the damping material using the single lap joint test configuration. Of particular interest was the effect of the damping material thickness on the measured shear modulus. Based on the analyses, single lap joint iv testing was performed to investigate the in situ shear modulus and shear strength of embedded damping materials in glass fiber/vinyl ester composite laminates. Quasi-static testing was performed to measure damping material properties as well as assess structural integrity and bond compatibility. Additionally, fully reversed cyclic loading was performed followed by quasi-static loading to failure to investigate bond durability. Through the use of digital image correlation, strain fields within the damping material were obtained for use in assessing the effects of specimen geometry and strain measurement methodologies. The results of this investigation suggest that the single lap joint test method can be implemented for accurately measuring the in situ properties of embedded damping materials and the structural integrity of the composite laminate. |
