Assessing the Interfacial Dynamic Modulus of Biological Composites

Biological composites (biocomposites) possess ultra-thin, irregular-shaped, energy dissipating interfacial regions that grant them crucial mechanical capabilities. Identifying the dynamic (viscoelastic) modulus of these interfacial regions is considered to be the key toward understanding the underlying structure–function relationships in various load-bearing biological materials including mollusk shells, arthropod cuticles, and plant parts. However, due to the submicron dimensions and the confined locations of these interfacial regions within the biocomposite, assessing their mechanical characteristics directly with experiments is nearly impossible. Here, we employ composite-mechanics modeling, analytical formulations, and numerical simulations to establish a theoretical framework that links the interfacial dynamic modulus of a biocomposite to the extrinsic characteristics of a larger-scale biocomposite segment. Accordingly, we introduce a methodology that enables back-calculating (via simple linear scaling) of the interfacial dynamic modulus of biocomposites from their far-field dynamic mechanical analysis. We demonstrate its usage on zigzag-shaped interfaces that are abundant in biocomposites. Our theoretical framework and methodological approach are applicable to the vast range of biocomposites in natural materials; its essence can be directly employed or generally adapted into analogous composite systems, such as architected nanocomposites, biomedical composites, and bioinspired materials.

Deformation of Composite Laminates Induced by Surface Bonded and Embedded Piezoelectric Actuators

In this work, piezoelectric (PZT) actuators were surface bonded on or embedded in a composite laminate and subjected to an electric voltage across the thickness, resulting in a bending effect on the composite laminate. An analytical expression of the deflection of a simply supported cross-ply composite laminate induced by distributed piezoelectric actuators was derived on the basis of classical plate theory and composite mechanics. The theoretical solution can be used to predict the deformation of the composite laminate. Series of parametric studies were performed to investigate the effects of location, size, and embedded depth of PZT actuators on the composite laminate deformation. The analytical predictions were verified with finite element results. A close agreement was achieved. It demonstrated that the present approach provided a simple solution to predict and control the deformed shape of a composite laminate induced by distributed PZT actuators.

Application of Conjugate Simulation for Determination of Temperature and Stress Distributions During Curing Process of Pre-Impregnated Composite Fibers

The composites made of continuous fibers in the form of unidirectional and fabric prepregs are widely used in many fields of engineering for the production of lightweight and durable parts or whole structures. To achieve this, we not only need to possess knowledge of the composite mechanics, but also have to master the technology. In most cases, particularly for parts with advanced geometric shapes, autoclaving technique is used. The success of the carried out process occurs when the prepreg reaches the proper temperature throughout its volume in the specified time, where there are no overheated or unheated zones as well as when the prepreg is correctly pressed against the mold. In order to ensure adequate stiffness, the mold has much greater thickness than formed composite and the stiffening ribs. The result is that the time required for prepreg heating is greatly extended. To prevent this, the appropriate electric heaters embedded in the silicone grips are used.The paper presents problems related to the mold structures and application of numerical methods aiming at early verification of the temperature and stress distribution. The coupled analysis of CFD (computational fluid dynamic) and heat transfer structural simulations were performed in Abaqus program. The studies were carried out for the airfoil fragment. A total of 12 simulations were conducted, 6 cases in which heat was supplied only from air flowing through the autoclave and 6 cases which included heaters inside the silicone grips. In the result the inhomogeneity of prepreg heating for each of the mold geometry was compared, and the average temperature was obtained after 60 seconds from the process initiation. Both the pressure inside the silicone grips (before inserting the mold into the autoclave) and the non-uniform temperature distribution result in the formation of stresses whose values were analyzed for molds made of aluminum. For this purpose the temperature dependent elastic – plastic material model was used for aluminum molds.

Numerical characterization and simulation of the three-dimensional tubular woven fabric

Three-dimensional tubular woven composite as a kind of special textile structural material is mainly used in oil and natural gas industry due to the advantages of the mechanical uniform circular shape and the provided properties. In order to comprehend the mechanical properties of the fabric in advance, modeling the three-dimensional tubular woven fabric is very important based on the actual weaving process parameters and specific structural data. In this paper, numerical characterization was performed and geometric model was constructed for this kind of three-dimensional tubular woven fabric. The geometric model of the 3D tubular woven fabric was established first based on the minimal repeating structural unit, and then a set of code including the positioning yarn coordinates and the topological relationship of the positioning yarn and non-positioning yarn was described. Furthermore, the three-dimensional tubular woven fabric was simulated under OpenGL platform according to the assumptions of the yarn cross-section and yarn path that was described by cubic B-spline curves. The proposed simulation method will contribute to the fabric structure simulation system used in the calculation of the fiber volume fraction, the distribution of voids and the prediction of composite mechanics.

Multi-Scale Energy Analysis Method during Automated Fibre Placement Process

Automated fibre placement (AFP) is an advanced technology for composite lay-up. However, analysis on mechanical properties used by experiments or macroscopic theories during AFP process suffers from some restrictions, because multi-scale effect of laying tows and their manufacturing defects could not be considered. This contribution proposes a novel anti-sequential multi-scale analysis method based on concurrent/sequential multi-scale analysis method. In order to establish a coupling mechanism among different scales, multi-scale energy transfer model is presented and emphatically analysed through composite mechanics and classical mechanics. Furthermore, taking a Bisphenol A epoxy matrix prepreg tow as an example, an application is employed to verify the feasibility of the method and model. Finally, application field for processing optimization is introduced and prospected.