J. Compos. Sci., Volume 2, Issue 4 (December 2018) – 17 articles

In this paper, we propose a novel systematic procedure to minimize the discrepancy between the numerically predicted and the experimentally measured fiber orientation results on an injection-molded part. Fiber orientation model parameters are optimized simultaneously using Latin hypercube sampling and kriging-based adaptive surrogate modeling techniques. Via an adequate discrepancy measure, the optimized solution possesses correct skin–shell–core structure and global orientation evolution throughout the considered center-gated disk. Some non-trivial interaction between these parameters and flow-fiber coupling effects as well as their quantitative importance are illustrated. The parametric fine-tuning of orientation models mostly leads to a better agreement in the skin and shell regions, while the coupling effect via a fiber-dependent viscosity improves prediction in the core. Full article

The effect of the hybridization of a triblock copolymer and a rigid TiO₂ nanofiller on the tensile, fracture mechanics and thermo-mechanical properties of bisphenol F based epoxy resin were studied. The self-assembling block copolymer, constituted of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer was used as a soft filler, and TiO₂ nanoparticles were employed as rigid modifiers. Toughening solely by block copolymers (BCP’s) led to the highest fracture toughness and fracture energy in the study, K_Ic = 2.18 MPa·m^1/2 and G_Ic = 1.58 kJ/m². This corresponds to a 4- and 16-fold improvement, respectively, over the neat reference epoxy system. However, a reduction of 15% of the tensile strength was observed. The hybrid nanocomposites, containing the same absolute amounts of modifiers, showed a maximum value of K_Ic = 1.72 MPa·m^1/2 and G_Ic = 0.90 kJ/m². Yet, only a minor reduction of 4% of the tensile strength was observed. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening mechanisms of the nanocomposites. Full article

In this paper, an icosahedral non-body-centered model is presented to simulate the periodic structure of a general class of homogeneous particulate composites, by predicting the particle arrangement. This model yielded three different variations, which correspond to three different deterministic particle configurations. In addition, the concept of a boundary interphase between matrix and inclusions was taken into account. In this framework, the influence of particle vicinity on the thermomechanical properties of the overall material was examined in parallel with the concept of boundary interphase. The simultaneous consideration of these two basic influential factors constitutes the novelty of this work. Next, by the use of this advanced model, the authors derived a closed-form expression to estimate the thermal conductivity of this type of composite. To test the validity of the model, the theoretical predictions arising from the proposed formula were compared with experimental data found in the literature, together with theoretical results obtained from several accurate formulae derived from other workers, and an adequate accordance was observed. Full article

In industry, manufacturing has a huge imprint on structural design; which particularly holds for composites. This is caused by complex interaction of geometry, process parameters and material quantities e.g., fiber orientation. This interaction yields a wide variety of feasible designs, which severely differ in costs and structural performance, measured in mass, stiffness and strength. In order to cope most effectively with this complexity, this paper discusses a weak artificial intelligence, emulating human expertise on composite manufacturing. This approach is extended such that the used knowledge-based system is capable of providing a reason for having determined a certain level of manufacturing effort. Moreover, this extension also provides advice pointing into the direction of optimal improvement. These novelties may be used during designing, optimization and post-processing. These three cases are herein discussed by applying it onto an automotive structure. Full article

Skin injury is the most common type of injury, which manifests itself in the form of wounds and cuts. A minor wound repairs itself within a short span of time. However, deep wounds require adequate care and sometime clinical interventions such as surgical suturing for their timely closure and healing. In literature, mechanical properties of skin and other tissues are well known. However, the anisotropic behavior of wounded skin has not been studied yet, specifically with respect to localized overstraining and possibilities of rupture. In the current work, the biomechanics of common skin wound geometries were studied with a biofidelic skin phantom, using uniaxial mechanical testing and Digital Image Correlation (DIC). Global and local mechanical properties were investigated, and possibilities of rupture due to localized overstraining were studied across different wound geometries and locations. Based on the experiments, a finite element (FE) model was developed for a common elliptical skin wound geometry. The fidelity of this FE model was evaluated with simulation of uniaxial tension tests. The induced strain distributions and stress-stretch responses of the FE model correlated very well with the experiments (R² > 0.95). This model would be useful for prediction of the mechanical response of common wound geometries, especially with respect to their chances of rupture due to localized overstraining. This knowledge would be indispensable for pre-surgical planning, and also in robotic surgeries, for selection of appropriate wound closure techniques, which do not overstrain the skin tissue or initiate tearing. Full article

The paper presents finite element modelling and thermomechanical analysis on the tensile properties of layered aluminium 1050 metal foil parts made by composite metal foil manufacturing. In this paper, a three-dimensional finite element model was developed and validated through experiments to analyse thermal effects on the tensile properties of 200-μm-thick aluminium 1050 metal foils. The effects of thermal stress and strain were studied by carrying out transient thermal analysis on the heated plates used to join the 200-μm-thick metal foils together using a special brazing paste. A standard tensile test at ambient temperature was carried out on the resulting layered dog bone specimens to analyse the thermal effects on the individual layers of metal. The investigations were precisely designed to assess the effect of heat provided amid the brazing operation to join the metal thwarts together as a layered structure and whether it assumed a part in affecting the tensile properties of the final products when contrasted to a solid aluminium 1050 dog bone specimen of the same dimensions. Corrosion testing was also carried out on dog bone specimens made from varying thickness foils (50 μm, 100 μm, and 200 μm) of aluminium 1050 to assess the effect of corrosion on the tensile strength and elongation. The results showed that the specimens did not face the problem of galvanic corrosion of the foil–bond interface. Microstructural analysis was also carried out to analyse the fracture modes of the tested specimens after corrosion testing. Full article

Most existing studies conducted on fiber-reinforced polymer (FRP)-confined concrete have considered circular and square concrete columns, while limited studies have considered columns with rectangular sections. Studies have confirmed that the circular cross-sections exhibited higher confinement effectiveness, whereas in the case of non-circular cross-sections the efficiency of FRP confinement decreases with an increase of the sectional aspect ratio and there is no significant increase, particularly for columns with the aspect ratio of 2.0. As recently suggested by researchers, to significantly increase the effectiveness of FRP-confinement for these columns involves changing a rectangular section into an elliptical or oval section. According to the literature, most of the existing confinement models for FRP-confined concrete under axial compression have been proposed for columns with circular and rectangular cross-sections. However, modeling of the axial strength and strain of concrete confined with FRP in elliptical cross-sections under compression is limited. Therefore, this paper provides new expressions based on limited experimental data available in the literature. For a sufficient amount of FRP-confinement, the threshold value was proposed to be 0.02. Finally, the accuracy of the proposed model was verified by comparing its predictions with the same test database, together with those from the existing models. Full article

There is significant work published in recent years about natural fibres polymeric composites. Most of the studies are about the characterization of natural fibres and their comparison with conventional composites regarding mechanical behaviour and application performance. There are dozens of types of natural fibres with different properties influencing their use, or not, in specific industrial applications. The natural origin of these materials causes, in general, a wide range of variations in properties depending mainly on the harvesting location and conditions, making it difficult to select the appropriate fibre for a specific application. In this paper, a comprehensive review about the properties of natural fibres used as composite materials reinforcement is presented, aiming to map where each type of fibre is positioned in several properties. Recent published work on emergent types of fibres is also reviewed. A bibliometric study regarding applications of natural fibres composites is presented. A prospective analysis about the future trends of natural fibres applications and the required developments to broaden their applications is also presented and discussed. Full article

The identification and classification of acoustic emission (AE) based failure modes are complex due to the fact that AE waves are generally released simultaneously from all AE-emitting damage sources. To fully understand the occurrence of damage and the damage evolution law of 3D braided composites, the tensile response characteristics and failure mechanisms of such composites were revealed by experiments, followed by frequency domain analyses. The results indicated good correlation between the number of AE events and the evolution of damage in 3D braided composites. After an AE signal was decomposed by the Hilbert–Huang transform (HHT) method, it might extract and separate all damage modes included in this AE signal. Additionally, the frequency saltation in the HHT spectra implied changes in the failure mode of the 3D braided composites. This study provides an effective new method for the analysis of the tensile fracture mechanism in 3D braided composites. Full article

In this paper, low-cost, aluminum-based composite metal foams are produced by the gravity die casting technique using lightweight expanded clay (LECA) as space holders. The influence of the voids generated by LECA particles on the syntactic composite samples density and mechanical behavior is characterized by quasi-static uniaxial compression. It is shown that smaller particles generate higher relative densities and a reduction in the value of densification strain. The use of larger particle diameter promotes an increase in yield strength and a more stable plateau region of the stress–strain curve, leading to higher values of crushing energy absorption. The influence of the internal structure on these experimental results is correlated with elasto-plastic numerical simulations, and it is suggested that a small mismatch in LECA particle diameter is advantageous for enhancing mechanical properties. Full article

The papers published in this special edition of the Journal of Composites Science will give the polymer engineer and scientist insight into what the existing challenges are in the discontinuous fiber composites field, and how these challenges are being addressed by the research community. [...] Full article

The present paper gives details of the structural response of titanium-based fiber metal laminates (TFML) subjected to high velocity impact. Dynamic perforation behavior of two different sample configurations, TFML-2/1 and 3/2 are presented. The behavior of the metal and composite layer is defined using two independent appropriate constitutive material models. Both experimental and numerically predicted residual velocity follows the Recht-Ipson model variation with impact velocity. Being larger in thickness, residual velocity, peak contact force and total energy absorbed were found to be larger for TFML-3/2 than 2/1. However, the contact duration was rather insignificantly affected. Having similar metal volume fraction (MVF), energy dissipated by means of plastic deformation of metal layers was found to be constant for both TFML configurations that were considered. The axisymmetric loading, boundary conditions and having balanced material property distribution along the principle axes resulted in doubly symmetric damage surfaces, both layer-wise and overall. The developed finite element (FE) model adequately simulated the contact behavior and all of the experimentally realized damage modes in the metal and composite layers and confirmed its reliability. Having limited experimental information, the obtained numerical information allows one to briefly understand the dynamic perforation behavior of TFML laminates. Full article

The influence of stacking sequence and resin rich (polyester veil cloth) layers, which were used to improve the adhesion between carbon fiber/epoxy (CFRP) and aluminum layers (AL), on the uniaxial tensile response of carbon fiber reinforced aluminum laminates (CARALL) was investigated in this research study. The metal volume fraction was varied to prepare two types of CARALL laminates having a 3/2 configuration with the help of a vacuum press without using any adhesive film. Numerical simulations were performed by utilizing commercially available finite element (FE) code, LS-Dyna to predict the tensile response of these laminates with initialization of predicted thermal residual stresses that developed during curing of laminates. Delamination failure was considered in the numerical simulation by utilizing the well-known B-K mixed-mode damage propagation model. It was found that addition of epoxy resin rich (polyester veil cloth) layers used for enhancement of interfacial bond adhesion and to ensure no separation between AL-CFRP layers increased the tensile strength of CARALL laminates. Full article

This work is concerned with the study of the influence of impactor’s velocity parameters, impactor’s geometry, the target plate properties, and thickness, on the response of a tropical wood plastic composite (WPC) Azobé/urea formaldehyde (Az/UF) plate under impact loading. Variations of the impact force, displacement, deformation, and impact energy of the specimens with weight fractions of 10, 20, 30, 40, and 50% have been considered in finite element analysis (FEA) simulations. The simulations of the Charpy and of a drop weight impact test on the WPC were carried out using the explicit dynamics module of ANSYS Workbench, which handles problems of dynamic loading of a short duration for 2D and 3D analyses. Contact laws that account for the compressibility of the interacting bodies (the standard steel impactor and the WPC target plate), have been used. The results show that the displacements decrease in contrast to the increase of the wood filler content, and vary in the 6.8–9.0 mm interval. From an energetic point of view, it is observed that the maximum absorbed energy is between 40 and 50% for the Azobe flour wt.%, with energy absorption rates of 28% and 26% of the total energy. These results are in agreement with those reported in previous experimental investigations on hybrid WPCs filled with wood flour and glass fibers, which produce an energy absorption rate of 24–26%. These results promote the applicability of Azobé tropical wood in fabricating WPCs for impact loading situations. Full article

Functionally graded composite materials may constitute an advantageous alternative to engineering applications, allying a customized tailoring capability to its inherent continuous properties transition. However, these attractive characteristics must account for the uncertainty that affects these materials and their structures’ physical quantities. Therefore, it is important to analyze how this uncertainty will modify the foreseen deterministic response of a structure that is built with these materials, identifying which of the parameters are responsible for a greater impact. To pursue this main objective, the material and geometrical parameters that characterize a plate made of an exponentially graded material are generated according to a random multivariate normal distribution, using the Latin hypercube sampling technique. Then, a set of finite element analyses based on the first-order shear deformation theory are performed to characterize the linear static responses of these plates, which are further correlated to the input parameters. This work also considers the constitution of statistic models in order to allow their use as alternative prediction models. The results show that for the plates that were analyzed, the uncertainty associated with the elasticity modulus of both phases is mainly responsible for the maximum transverse deflection variability. The effectiveness of the statistical models that are built are also shown. Full article

The possibility of designing composite panels with non-uniform stiffness properties offers a chance for achieving highly-efficient configurations. This is particularly true for buckling-prone structures, whose response can be shaped through a proper distribution of the membrane and bending stiffnesses. The thermal buckling behaviour of composite panels is among the aspects that could largely benefit from the adoption of a variable-stiffness design, but, in spite of that, it has rarely been addressed. The paper illustrates a semi-analytical approach for evaluating the thermal buckling response of variable-stiffness plates (VSP) by considering different boundary conditions. The formulation relies upon the method of Ritz and a variable-kinematic approach, leading to a computationally efficient implementation, which is particularly useful for exploring the larger design spaces, typical of variable-stiffness configurations. Due to the possibility of choosing the underlying kinematic approach as an input of the analysis, the formulation is not restricted to thin plates, but is suitable for analyzing the response of thick plates as well. Novel results are derived, which can be useful for benchmarking purposes and for gathering insight into the mechanical behaviour of variable-stiffness plates. Furthermore, the importance of transverse shear flexibility is illustrated with respect to the boundary conditions as well as the degree of steering of the fibers. Full article

This paper aims at investigating the general axial behavior of long circular concrete-filled, fiber-reinforced polymer (FRP) tube (CFFT) columns internally reinforced with different longitudinal rebars. A total of seven CFFT and three reinforced concrete (RC) columns served as control specimens for comparisons and were constructed and tested under cyclic axial loading until failure. The test parameters were: (1) internal reinforcement type (steel, glass fiber-reinforced polymer (GFRP) or carbon fiber-reinforced polymer (CFRP)) and amount; (2) GFRP tube thicknesses; and (3) nature of loading. All columns had 1900-mm in height and 213-mm in diameter. Examination of the test results has led to a number of significant conclusions in regards to the trend and ultimate condition of the axial stress-strain behavior, mode of failure of tested CFFT columns, and plastic strains. As expected, an increase in the FRP tube thickness (or stiffness) resulted in an increase in the strength and strain enhancement ratios. The validity of the available design provisions for predicting the ultimate load-carrying capacity of tested columns is also highlighted. Full article