Achieving of sandwich-like laminated composite materials for robust superhydrophobicity, rapid photochromism and photo-mask writable media

Photochromic materials with anti-water properties have impressed practical values, but their applications are severely hindered by poor stability and slow colour-switching rate. Inspired by the superhydrophobicity of lotus leaf and...

MECHANICAL TESTING OF LAMINATED COMPOSITE MATERIALS FOR PROSTHETIC SOCKETS

The mechanical properties of the composite materials for prosthetic sockets are a key determinant of the quality and usability of prostheses. Our aim was to compare the existing materials used in production at our institution with some modified, potentially improved materials. We conducted an industrial experiment. The existing material (A) was compared with three newly produced materials that introduced changes in the lamination process: B1, where an infusion spiral tube was added; B2, where the resin was degassed; and B3, where a mesh and peel ply were used. The specimens underwent laboratory strength testing. The strength measurements were statistically analysed using one-way analysis of covariance (ANCOVA) that was adjusted for specimen thickness because of the observed negative correlation of thickness with strength. Material A had the highest bending strength, on average, but there were no statistically significant differences in the bending strength between the materials after adjusting for the specimen thickness (p = 0.941). Materials B1 and B2 exhibited statistically significantly lower tensile strengths than material A (p < 0.001). Material B3 had the lowest average tensile strength, but it could not be statistically distinguished from the others, because of the significantly larger average specimen thickness. The compressive strength was tested only for materials B1, B2 and B3; their averages did not differ statistically significantly (p = 0.291). Laboratory strength testing provided important insights into the differences between the various laminated composite prosthetics materials. We did not reach our initial goal to produce a better material, but we will continue our research and development in this field with a more systematic, technological approach.

HIGH ENERGY WIDE AREA BLUNT IMPACT OF COMPOSITE AIRCRAFT STRUCTURES PART B: TESTING AND INTERNAL DAMAGE MODES

Modern aircraft structures constructed from high strength laminated composite materials present a challenge in the detection of damage resulting from impact events. Broad-area contact from large sized or blunt radius objects furthermore create conditions in which significant internal damage can result, while leaving low (or even no) externally visible indications of damage being present. Composite fuselage structures subjected to high energy wide area blunt impact (HEWABI) sources have been studied. These impact sources act over a wide area and can possibly damage multiple internal structural elements. HEWABI sources of concern are generally heavy ground service equipment (GSE) such as belt loaders, cargo loaders, catering trucks, etc., which have soft rubber/elastomeric bumper-type pads mounted at locations where the GSE could contact the aircraft. Of particular interest in this study is the formation of damage in composite frame and shear tie components during HEWABI events occurring near the passenger floor joint. Carbon/epoxy composite test specimens reflecting modern composite fuselage features were designed and fabricated having continuous shear ties and representative stiffness interaction between the floor beam and circumferential frame members. Quasi-static and slow speed tests (representing impact) conducted using rubber bumper faced indentors developed significant internal damage to internal components. Specifically, fiber failures and large-size crack formation in shear ties, frames, and stringers occurred with low/no external observability in the external skin. A clear quantitative understanding of damage modes and damage location that could result from HEWABI events is important for establishing damage size criteria in the evaluation of a structure’s residual strength and damage tolerance capability.

FATIGUE DAMAGE MODELING IN LAMINATED COMPOSITES BY USING RX-FEM AND STRENGTH TRACKING METHOD

The durability and residual load carrying capacity of composite materials and structures is of critical importance for increasing their application across the industry. Regularized eXtended Finite Element Method (Rx-FEM) framework for discrete modeling of damage evolution and interaction in laminated composite materials under fatigue loading has been extended to include residual Strength Tracking (ST) method in the Mesh Independent Crack (MIC) insertion constitutive modeling as well as in the initiation phase of the fatigue Cohesive Zone Model (CZM). The ST method was initially proposed for semi empirical analysis of IM7/8852 open-hole specimen test S-N data under spectrum loading and variable R -ratios (R = 0.1, 5, and -1). In the present work, the ST method is implemented as a component of high-fidelity progressive damage analysis framework and is combined with damage variable incremental update technique for the propagation phase within the CZM formulation. 3D validation examples investigating the solution stability under constant amplitude fatigue with respect to the cycle increment size are presented and demonstrate the solution stability within a feasible range of cycles per step.

Study on the Relationship between the Bonding Surface and Mechanical Properties of PLA/Epoxy Laminated Composites

Rule of mixtures (RoMs) of composite materials is continuously modified according to different component materials and their composition forms to play the role of theoretical verification and evaluation. This paper studied the regular relationship between the bonding surface and mechanical performance of the composites. The three bonding surface designs were made into PLA/EP test samples by 3D printing technology. The tensile and bending properties of the composite materials were proved to be stronger than the average of those of their component materials. The mechanical properties show regular changes with the bonding surface and structural design. The bonding surface between components is an important reference information that cannot be ignored for the performance prediction and adjustment of laminated composite materials.