Mechanical Behavior Of Fiber-reinforced Composites Research Articles

Anisotropic microstructure dependent mechanical behavior of 3D-printed basalt fiber-reinforced thermoplastic composites

3D printing is a process of hierarchically fabricating three-dimensional microstructures by successively adding materials in a bottom-up manner. The technology has been rapidly advancing, especially in the manufacturing of high-strength, lightweight industrial composite materials. Thus far, many studies have focused on the spontaneous alignment of short reinforcing fibers that are subject to adjustment during the 3D-printing process, along with an inevitable void formation arising due to an intrinsic nature of the additive process. However, systematic examination of the 3D-printed anisotropic microstructures, related with a markedly high degree of fiber alignment and formation of voids in the matrix, has not been sufficiently conducted to analyze its effect on the anisotropic mechanical behaviors of fiber-reinforced composites. Here, we sought to examine in detail the internal morphology of fibers and voids in 3D-printed composites by 3D X-ray microscopy to explore their anisotropic architecture. The position, length, and alignment of fibers and voids were identified, visualized, and quantitatively characterized with a help of computational tomography (CT). Furthermore, the anisotropy approximation of the 3D-printed composites, precisely predicted through CT-assisted simulation, was derived based on the quantitative data obtained from the 3D reconstruction image. These measurements were effective in exploring the process-induced alignment nature of fibers and voids in the local region layers on the microscopic scale, and the corresponding microstructure resulted in a change in the elastic modulus of the composites with the printing direction. The comparative results showed that the experimental results were well supported by the simulation-based estimations, but did not exactly match the rule-of-mixture of the composites in terms of interfacial nature due to the distinctive microstructure with the fiber-to-matrix interface as well as the filament-to-filament interface.

The Effect of Stacking Sequence of Woven Bamboo on Mechanical Behavior of Fiber-Reinforced Composites

Natural fiber-reinforced composites are necessary to increase the use of polymer composite technology. This study investigates a specific type of bamboo species named Gigantochloa Scortechinii (Buluh Semantan), collected from the Bukit Larang Village in Melaka, Malaysia. Bamboo strips with average dimensions of 300 mm x 5 mm x 0.5 mm were weaved in plain-woven bamboo and divided into 2 to 6 laminate layers through 6 layers of E-glass epoxy subjected to the hand lay-up process to produce the hybrid composite. The hybrid composites were prepared in a stacking sequence of plain-woven bamboo and were characterized in their mechanical properties. The behaviors of the tensile strength, tensile modulus, flexural strength, flexural modulus, and impact strength improved in the 2-layer laminated hybrid sequences. Still, the opposite trend was observed for the hardness value with the 6-layer laminated mixed sequences. The morphology scanning electron microscopy (SEM) results supported the findings of the mechanical properties, which demonstrated the interaction between the EP and fibers with the selected stacking sequence. The works give sound basis decisions to engineers to apply the Bamboo laminated composites in construction materials and building decoration.

Physico-Mechanical Properties of the Poly(oxymethylene) Composites Reinforced with Glass Fibers under Dynamical Loading.

The paper evaluated the possibility of potential reinforcing of poly(oxymethylene) (POM) by glass fiber and the influence of fiberglass addition on mechanical properties under dynamic load. Four types of composites with glass fiber and another four with carbon fiber were produced. The fiber content ranged from 5% to 40% by weight. In the experimental part, the basic mechanical and fatigue properties of POM-based composites were determined. The impact of water absorption was also investigated. The influence of fiber geometry on the mechanical behavior of fiber-reinforced composites of various diameters was determined. To refer to the effects of reinforcement and determine the features of the structure scanning electron microscopy images were taken. The results showed that the addition of up to 10 wt %. fiberglass increases the tensile properties and impact strength more than twice, the ability to absorb energy also increases in relation to neat poly(oxymethylene). Fiber geometry also has a significant impact on the mechanical properties. The study of the mechanical properties at dynamic loads over time suggests that composites filled with a smaller fiber diameter have better fatigue properties.

Composites of Portland cement and fibers ofGuadua angustifoliaKunth from Colombia

The main objective of this work is to study the flexural mechanical behavior of fiber-reinforced composites made of ordinary white Portland cement combined with Guadua bamboo from Colombia (known as Guadua angustifolia Kunth or just guadua). Fibers were carefully removed from the stem with a knife in a manual process, and then samples with 0.0, 4.0, and 8.0 wt% of fibers were fabricated. No further treatment was used in order to make the process as simple and inexpensive as possible for applications in the construction and building materials industry. Mechanical and structural characterization was analyzed by optical microscopy and scanning electron microscopy. Density compressive strength and Weibull distribution graphs were included in this work. The results show that flexural strength increases as the fiber content is increased. They also show a very good impregnation of the cement in the fibers, which validated the use of fiber from the bamboo culm. It is feasible that these composites can be used in the construction and building materials industry on a large scale for noncritical ultimate strength applications because of the low costs associated with processing the fibers.

Stress-Strain Characterization in Fiber-Reinforced Composites by Digital Image Correlation

Composite materials are widely used in structural mechanics as they can withstand high loads; although after a while, they can present relative strain due to these loadings. In the present work, it is implemented digital image correlation using one laser-beam and the speckles created by its reflection to describe the mechanical behavior of fiber-reinforced composites submitted under compression test. Composites were tested in two set of arrays: the first was done with fibers orientated parallel to the load and the second was done with fibers randomly orientated, as it is known that the stress-strain evolution change according to the orientation of the fibers. Our method allows us to evaluate the heterogeneous strain evolution observed during the tests. Validity of optical strain-measurements is assessed against the results of an universal testing machine, a good correlation was found by comparing the results.

Micromechanical analysis of transverse damage of fibre-reinforced composites

The mechanical behaviour of fibre-reinforced composites under transverse tension, compression and shear is studied using computational micromechanics. The representative volume element is constructed for fibre’s random distribution. The Drucker–Prager model and cohesive zone model are used to simulate the matrix damage and interfacial debonding, respectively. The stress distribution along the interface is studied using the model with only one fibre embedded in the matrix. It is found that the interface tensile failure at the equators of fibre firstly occurs under transverse tension; the interface shear failure firstly occurs under transverse compression; both the interface tensile failure and shear failure occur under transverse shear. The direction of fracture plane is perpendicular to the loading direction under transverse tension, 52.5° with the perpendicular direction under compression and 7.5° with the perpendicular or vertical direction under shear, respectively.

Simple constitutive model for nonlinear response of fiber-reinforced composites with loading-directional dependence

Polymeric composites generally exhibit different nonlinear response in tension and compression tests. In this study, Sun and Chen’s one-parameter plasticity model [Sun C.T. and Chen J.L., 1989. A simple flow rule for characterizing nonlinear behavior of fiber composites, J Compos Mater 29, 457–463] is extended to incorporate the loading-directional dependence on the plastic flow in composite laminates. Off-axis specimens of unidirectional carbon/epoxy composites were tested in compression and tension. Based on experimental results of compression tests, a simple two-parameter constitutive model for characterizing nonlinear mechanical behavior of fiber-reinforced composites was established. Finally, comparison of model predictions with experimental results of off-axis tension tests indicated a good correlation between the two. The developed simple plasticity model can explain the difference of nonlinear response in tension and compression tests.

Thermal shock on interfacial adhesion of thermally conditioned glass fiber/epoxy composites

The fiber/matrix adhesion is most likely to control the overall mechanical behavior of fiber-reinforced composites. An interfacial reaction may result in various morphological modifications to polymer matrix microstructure in proximity to the fiber surface. The interactions between fiber and polymer matrix during thermal conditioning and thermal shock are important phenomena. Thermal stresses were built-up in glass fiber-reinforced epoxy composites by upthermal shock cycles (negative to positive temperature exposure) for different durations and also by downthermal shock cycles (positive to negative temperature exposure). The concentration of thermal stresses often results in weaker fiber/matrix interface. A degradative effect was observed in both modes for short shock cycles and thereafter, an improvement in shear strength was measured. The effects were shown in two different crosshead speeds during short-beam shear (SBS) test.

On the mechanical behavior of fiber-reinforced composites

In this paper, the derivation of the state potential is presented to model the mechanical behavior of fiber-reinforced composites. It allows matrixcracking, interfacial debonding and sliding to be accounted for in the framework of Continuum Damage Mechanics. An application is performed on a unidirectional SiC/SiC composite.

A model for predicting micromechanical interfacial adhesion in polymer composites

The mechanical behavior of fiber-reinforced composites is largely determined by adhesion at the fiber-matrix interface. Thus, a fundamental understanding of the interfacial region and a quantitative characterization of the level of interfacial adhesion can contribute to an evaluation of the mechanical behavior and performance of composite materials. Among numerous techniques for interface characterization, the vibration damping method has attracted continually more attention because it provides sensitive and nondestructive detection of the interfacial region in composites. In the research presented here, a new optical system for measuring vibration damping was introduced, and a model for evaluating the interfacial adhesion between fiber and matrix from a damping parameter was developed. A quantitative relationship between the dynamic (vibration damping) and static (interfacial shear strength) adhesion measurements was established. The experimental data from glass-fiber-reinforced epoxy resin composites with different interfacial treatments showed good agreement with the theoretical model.

Dynamic Mechanical Behavior of Fiber-Reinforced Composites: Measurement and Analysis

This paper describes analytical and experimental efforts to find the internal damping and elastic stiffness of E-glass fiber-reinforced epoxy beams under flexural vibration. Stiffness and damping are expressed in terms of effective complex moduli. The parameters considered in the study are geometric configuration, vibration frequency, and vibration amplitude. Comparison. of measured values of the complex moduli with predicted moduli and with predicted bounds on the moduli shows that, for small amplitudes, the predicted values are reasonably accurate. Damping and stiffness are independent of amplitude as long as the maximum strain amplitude does not exceed the threshold strain for material damage. Once this threshold strain is exceeded, however, permanent changes occur in damping and stiffness. The resulting increase in damping is much more significant than the corresponding reduction in stiffness.

On the mechanical behaviour of fibre-reinforced crystalline materials

A theoretical analysis of the mechanical behaviour of fibre-reinforced crystalline materials is presented in terms of the elastic and plastic properties of the components. Certain room temperature mechanical behaviour of fibre-reinforced composites is predicted using an ‘inclusion’ concept and from geometric, clastic, statistical distribution and plastic strength considerations. Certain elevated temperature mechanical behaviour of fibre-reinforced composites is predicted using a universal viscoelastic concept.