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Nanoindentation (nanometer scale, extremely small) and impact (microsecond scale, extremely fast) experiments are two important techniques for characterizing modern material systems. However, these two experiments were often studied individually. In this pilot study, a multiscale indentation mechanics approach is proposed to correlate these two very different mechanics events acting on the same target materials using a spherical indenter and a projectile. The contact stiffness of nanoindentation of a target material is fitted using Hertz's contact law, and then the contact stiffness of impact is obtained using a simplified multiscale relation. Therefore, the maximum impact force of a projectile impact can be predicted by inputting the impact energy and the contact stiffness of impact. The above new approach was validated by drop-weight impact experiments of polymers and structural composite materials subjected to low-energy impact. Results show that only a few minutes are needed to predict the maximum impact force. Graphical Abstract [ABSTRACT FROM AUTHOR]

An experimental study of the modified butterfly shear sample was undertaken for polymer matrix composites using three quasi-isotropic IM7/977-3 laminates. This study used 3D digital image correlation (DIC) to observe and quantify the severe shear strain concentrations developed by compressively loading the modified butterfly geometry laminates. Interrupted X-Ray computed tomography (X-Ray CT) was used to understand the failure mechanisms present in the region of shear strain. By choosing to conduct interrupted testing, the progressive nature of the damage could be observed. At ultimate failure, extensive damage in the region of high shear strain was observed using post testing inspection with X-Ray CT. The mechanical testing was accompanied by numerical simulations for each laminate. The damage predicted by the numerical simulations was shown to be consistent with the damage observed with the post failure inspection via X-Ray CT. Stress components caused by free-edge effects were also quantified, and shown to have a minimal impact on the failure mode in the region of interest. [ABSTRACT FROM AUTHOR]

Previous approaches to measure the through-thickness Young's modulus of a composite laminate often employed complicated specimens and test procedures, so very few through-thickness Young's moduli were reported. An efficient spherical nanoindentation approach was developed to measure the through-thickness Young's moduli of a woven fibric glass-fiber composite laminate. In this paper, the same approach is extended to the modulus measurement of four carbon fiber/epoxy IM7/937-7 laminates with complicated stacking sequences. The measured through-thickness Young's moduli were consistent with the transverse Young's modulus of the same composite system. Results show that the stacking sequences have little influence on the through-thickness Young's moduli, which could be explained by classical lamination theory for a thin composite laminate. [ABSTRACT FROM AUTHOR]