Mechanical Respond and Failure Mode of Large Size Honeycomb Sandwiched Composites under In-Plane Shear Load.

The present work focuses on the in-plane shear respond and failure mode of large size honeycomb sandwich composites which consist of plain weave carbon fabric laminate skins and aramid paper core. A special size specimen based on a typical element of aircraft fuselage was designed and manufactured. A modified in-plane shear test method and the corresponding fixture was developed. Three large size specimens were tested. The distributed strain gauges were used to monitor the mechanical response and ultimate bearing capacity. The results show that a linear respond of displacement and strain appears with the increase of the load. The average shear failure load reaches 205.68 kN with the shear failure occurring on the face sheet, and the maximum shear strain monitored on the composite plate is up to 16,115 µÎµ. A combination of theoretical analysis and finite element method (FEM) was conducted to predict the shear field distribution and the overall buckling load. The out-of-plane displacement field distribution and in-plane shear strain field distribution under the pure shear loading were revealed. The theoretical analysis method was deduced to obtain the variation rule of the shear buckling load. A good agreement was achieved among the experiment, theoretical analysis, and FEM results. It can be concluded that the theoretical analysis method is relatively conservative, and the FEM is more accurate in case of deformation and strain. The results predicted by h element and p element methods are very close. The results of the study could provide data support for the comprehensive promotion of the design and application of honeycomb sandwich composites.

BMP7 enhances the effect of BMSCs on extracellular matrix remodeling in a rabbit model of intervertebral disc degeneration.

Intervertebral discs (IVDs) provide stability and flexibility to the spinal column; however, IVDs, and in particular the nucleus pulposus (NP), undergo a degenerative process characterized by changes in the disc extracellular matrix (ECM), decreased cell viability, and reduced synthesis of proteoglycan and type II collagen. Here, we investigated the efficacy and feasibility of stem cell therapy using bone marrow mesenchymal stem cells (BMSCs) over-expressing bone morphogenetic protein 7 (BMP7) to promote ECM remodeling of degenerated IVDs. Lentivirus-mediated BMP7 over-expression induced differentiation of BMSCs into an NP phenotype, as indicated by expression of the NP markers collagen type II, aggrecan, SOX9 and keratins 8 and 19, increased the content of glycosaminoglycan, and up-regulated ß-1,3-glucuronosyl transferase 1, a regulator of chondroitin sulfate synthesis in NP cells. These effects were suppressed by Smad1 silencing, indicating that the effect of BMP7 on ECM remodeling was mediated by the Smad pathway. In vivo analysis in a rabbit model of disc degeneration showed that implantation of BMSCs over-expressing BMP7 promoted cell differentiation and proliferation in the NP, as well as their own survival, and these effects were mediated by the Smad pathway. The results of the present study indicate the beneficial effects of BMP7 on restoring ECM homeostasis in NP cells, and suggest potential strategies for improving cell therapy for the treatment of disc diseases.