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This study experimentally investigated the effects of nanoparticle reinforcement on the buckling behavior of composite materials. Different sizes of carboxylic acid functionalized multi-walled carbon nanotubes were used as nanoparticles. E-glass fiber-reinforced composite materials with polymer matrix in the [0°/90°/0°/90°]s cross-ply array with and without carbon nanotube reinforcement were produced by hand lay-up and vacuum bagging. Three types of carbon nanotubes in different sizes and proportions of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight were added to the epoxy resin. For the buckling test, the samples with two clamped and two free sides were attached to the universal testing machine to apply a uniaxial compressive load. As a result of the experiments, it was found that the addition of carbon nanotube in certain proportions increases the critical buckling load of composite materials. The highest increase in the critical buckling load (26.10% increase) was achieved with a carbon nanotube reinforcement of 0.2% by weight, having an outer diameter of 10–20 nm, internal diameter of 5–10 nm, and length of 0.5–2 mm. As the carbon nanotube sizes added to the epoxy resin decreased, the buckling strength increased. [ABSTRACT FROM AUTHOR]

High injection pressure resin transfer moulding is a variant of resin transfer moulding in which the preform is compressed in a tool and resin is injected into the mould under very high pressure. The high injection pressure (>20 bar) introduces possible fibre washout that translates into manufacturing defects or causes inconsistencies in processing and leads to scatter in mechanical properties of composite parts. A model is presented which quantifies and provides insight into the influence of process variables such as clamping force and injection pressure on fibre washout distance (the one-dimensional model assumes a rigid preform). A generalised one-dimensional stress model for fibre washout is presented for regions that are impregnated with the resin and the regions that are dry. The model shows fibre washout to be significant at the beginning of the injection process. The model allows one to further refine the injection strategy by adjusting injection pressure to account for washout in high injection pressure resin transfer moulding. [ABSTRACT FROM AUTHOR]

In this work, biaxial buckling analysis of sandwich plates with symmetric composite laminated core and two functionally graded nanocomposite face sheets is carried out by a new improved high-order theory. The nanocomposite face sheets are carbon nanotube (CNT)-reinforced nanocomposites and the material properties of the nanocomposites plates are graded along the thickness and are estimated though the Mori–Tanaka approach. CNTs are assumed randomly oriented and aggregated into some clusters. The same third order theory is used for modeling of core and the faces sheets. The theory has third and second orders of z for in-plane and normal displacements, respectively. The principle of minimum potential energy is used to derive the equations of motion and boundary conditions. Analytical solution for static analysis of simply supported sandwich plates under biaxial in-plane compressive loads is presented using Navier’s solution. The effects of CNT volume fraction, CNT aggregation states, CNT distribution, biaxial loads ratio, and geometric dimensions of sandwich plate are investigated on the overall buckling of functionally graded carbon nanotube-reinforced nanocomposite sandwich plates. [ABSTRACT FROM AUTHOR]

Hybrid lattice cores for sandwich structures containing both solid struts and polymer foam are a recent option available to designers. These cores benefit from a synergistic effect in which the foam supports the slender struts against buckling in addition to carrying a portion of the applied loads directly. This work will optimize these hybrid cores to minimize unit cell density given compressive and shear strength constraints for a variety of unit cell configurations. An analytical model is developed for prediction of failure using the assumption that the foam is an elastic foundation that supports the struts; however, the unit cells are found to be optimal when no polymer foam is used. With the problem thereby simplified, analytical optimization solutions are derived and studied extensively, revealing qualitative insights about efficient lattice core designs. Optimal strut inclination angle, failure mode, and configuration are plotted against loading, which show that, for the large majority of strength constraints, the lowest unit cell density is achieved with tetrahedral cores whose struts fail in compressive yielding. [ABSTRACT FROM AUTHOR]

CCF300/5228A aero composite stiffened panels achieved absorbing saturation in hygrothermal condition (70℃ distilled water), whose absorbing process followed the Fick law. Many debonding and gaps of matrix to fibers could be observed after hygrothermal exposure by scanning electron microscope (SEM). Compressive experiments were conducted on unaged and aged composite stiffened panels. Failure modes of the two types of specimens are quite similar with several major ways, including the debonding and fracture of stiffeners together with the splitting and ripping of panel. Buckling patterns for both types of specimens are similar and characterized by buckling of panels between stiffeners and buckling of the middle two stiffeners. However, the bending direction of buckling mid-panel for aged specimens is opposite to that of the unaged at same position panel, which shows that hygrothermal condition influences the bending direction of buckling mid-panels seriously. There still exists a post-buckling process for aged specimens under axial compression, whose average buckling load and failure load decrease by 3.1% and 22.2% respectively, comparing to that of unaged specimens. [ABSTRACT FROM AUTHOR]

Textured surfaces, formed through wrinkling and folding, are observed abundantly in nature. We are especially motivated by the unique capabilities of some species of cuttlefish that camouflage themselves by rapidly switching from smooth to textured skin by expressing protuberances called papillae. Inspired by this, we developed a shape memory alloy–elastomer composite as a platform for reversible surface texture. A shape memory alloy wire embedded in an elastomer is forced to shrink due to Ohmic heating. This shrinkage is used to drive the reversible buckling of a thin stiff film attached to the elastomer surface. The platform is scalable, produces wrinkling patterns in the flip of a switch, operates at voltages under 10 V, and can be operated reversibly over multiple cycles. The amplitude and kinetics of the surface wrinkling are experimentally characterized. The wrinkle patterns appear and disappear in timescales ranging from tens of seconds to as little as a second depending on the voltage actuating the shape memory alloy wire. Finally, this platform can create reversible wrinkle patterns in a spatially reconfigurable fashion, that is, the location of the texture changes can be varied in real time. A two-dimensional shear lag model is developed to establish the important design parameters governing the formation of wrinkles. [ABSTRACT FROM AUTHOR]

Advanced grid stiffened composite cylindrical shell is widely adopted in advanced structures due to its exceptional mechanical properties. Buckling is a main failure mode of advanced grid stiffened structures in engineering, which calls for increasing attention. In this paper, the buckling response of advanced grid stiffened structure is investigated by three different means including equivalent stiffness model, finite element model and a hybrid model (H-model) that combines equivalent stiffness model with finite element model. Buckling experiment is carried out on an advanced grid stiffened structure to validate the efficiency of different modeling methods. Based on the comparison, the characteristics of different methods are independently evaluated. It is arguable that, by considering the defects of material, finite element model is a suitable numerical tool for the buckling analysis of advanced grid stiffened structures. [ABSTRACT FROM PUBLISHER]