Search

Low-velocity impact on fiber-reinforced polymer (FRP) composites may cause subsurface interface delaminations. In the case of such multiple delaminations, neighboring delaminations may grow and coalesce into larger delamination under post-impact loading. The resistance to such growth is substantially influenced by the strength and stiffness of epoxy resins used in FRP composite laminates. Therefore, the current study attempts to determine how adding carbon nanotubes (CNTs) to epoxy might potentially enhance the resistance to such delaminations. A three-dimensional (3D) finite element analysis has been carried out for laminates having single embedded delamination as well as two neighboring embedded delaminations to determine the interlaminar stresses and strain energy release rate using virtual crack closure integral. Results from the current analysis show that while parameters like shape, size, and relative spacing of delamination influence the growth, however in all the cases, adding CNTs to epoxy significantly improves the resistance to the growth of both single and interacting delaminations. The effect is observed to be more pronounced when the delaminations are closely spaced and tend to coalesce into a large delamination. [ABSTRACT FROM AUTHOR]

In this paper, determination of the accurate notch stress intensity factors (NSIFs) have been demonstrated using a recently proposed technique: The point substitution displacement technique (PSDT) for the sharp Vnotched configurations. In this technique, certain optimal point(s) on the notch flanks are obtained where the displacements are found to be highly accurate. Using the PSDT, the NSIFs are determined from the finite element (FE) displacements at these optimal point(s). The NSIFs of two pure mode I and two mixed mode (I/II) examples have been determined and excellent agreement of the present results with the published results is observed. The PSDT is efficient, robust and easy to be implemented in the available FE code. [ABSTRACT FROM AUTHOR]

Determination of accurate mixed mode stress intensity factors forms the basis for the understanding and analysis of mixed mode fracture. In this context, experimental methods for the measurement of stress intensity factors (SIFs) play a vital role. However, very few strain gage based techniques are available for measurement of mixed mode SIFs KI and KII in isotropic materials. In addition, no useful recommendations on appropriate radial locations of strain gages ensuring accurate SIFs are available in literature. Recently, authors have theoretically proposed a mixed mode strain gage technique and attempted to address the long standing problem of assessment of appropriate strain gage radial locations for the accurate measurement of the SIFs. They have shown that there exist certain gage radial locations called as optimal locations for the accurate measurement of SIFs, which can be easily assessed with their proposed methodology for any mixed mode (I/II) configurations. In the present investigation, experiments were conducted to study the efficacy of the authors' proposed mixed mode strain gage technique and existence and usefulness of the optimal strain gage locations in accurate measurement of SIFs KI and KII. The present experiments were also aimed to show the consequences of placing the gages at invalid or non-optimal gage locations. The experimental results clearly show that highly accurate mixed mode SIFs can be measured using the proposed mixed mode strain gage technique if the gages are pasted at the optimal locations. On the other hand, the results also exposed that highly erroneous and unacceptable measurement of SIFs can result if the gages are located at non-optimal locations. Furthermore, the present results clearly demonstrated the need of knowing the optimal strain gage locations a priori, which can be assessed using the methodology proposed recently by the authors. [ABSTRACT FROM AUTHOR]

In this work the dynamic stability of a rotating three layered symmetric sandwich beam with magnetorheological elastomer (MRE) core and conductive skins subjected to axial periodic loads has been investigated using finite element method (FEM). The derived governing equation of motion is in the form of a multi-degree of freedom Mathieu-Hill's equation with complex coefficients. The instability regions of the sandwich beam for the principal parametric resonance case have been determined by using the harmonic balance method. Effects of applied magnetic field, rotating speed, setting angle, hub radius, static load and dynamic load on the dynamic characteristics and instability regions of the sandwich beam are investigated. This work will find application in the passive and active vibration reduction of rotating sandwich structure using magnetorheological elastomer core, magnetic field and periodic axial load. [ABSTRACT FROM AUTHOR]