S. L. Kampe

Room-temperature strength and deformation of TiB2-reinforced near-γ titanium aluminides

A series of TiB2-reinforced near-γ titanium aluminide (Ti-Al) matrix composites have been produced in investment-cast form and characterized with respect to microstructure and tensile deformation. The Ti-Al matrices of the composites examined are based upon the binary composition Ti-47 Al (at. pct), with varying proportions (2 to 6 cumulative percent) of manganese, vanadium, chromium, and niobium. TiB2 has been introduced into the microstructuresvia XD* processing at levels of 7 and 12 vol pct and compared to unreinforced (0 vol pct TiB2), base variants. The influences of heat-treatment temperature and time have also been studied for each composition and reinforcement variant. The addition of dispersed TiB2 leads to a fine, stable, and homogeneous as-cast matrix microstructure. The measured TiB2 size within the composites examined ranged from 1.4 to 2.6 µm. Increasing the volume fraction of TiB2 leads to increased elastic moduli, increased ambient temperature tensile strengths, and in general, increased strain-hardening response. In some instances, the overall ductility of the alloy increases with the addition of TiB2 reinforcement. The flow stresses of both the monolithic and composite variants exhibit conventional power-law plasticity. The results indicate that the strengthening and the flow behavior in these composites are derived from both indirect and direct sources. Strengthening contributions are indirectly derived from the microstructural changes within the matrix of the composite that evolve due to the presence of the reinforcement during its evolution and development, for example, due to grain refinement and reinforcement-derived interstitial solid-solution strengthening. Direct contributions to strength are those that can be specifically attributed to the presence of the reinforcement during deformation,e.g., through the interaction of dislocations with the reinforcing particles. When the estimates of the indirect contributions are isolated and arithmetically removed from the magnitude of the total observed strength of the composite, the increase in flow stress correlates in all instances with the inverse square root of the planar interparticle spacing for all alloy compositions, heat treatments, and levels of strain examined.

Volume fraction effects on interfacial adhesion strength of glass-fiber-reinforced polymer composites

Abstract The performance of fiber-reinforced composites is often controlled by the properties of the fiber–matrix interface. Good interfacial bonding (or adhesion), to ensure load transfer from matrix to reinforcement, is a primary requirement for effective use of reinforcement properties. Thus, a fundamental understanding of interfacial properties and a quantitative characterization of interfacial adhesion strength can help in evaluating the mechanical behavior and capabilities of composite materials. A large number of analytical techniques have been developed for understanding interfacial adhesion of glass-fiber-reinforced polymers. Among these techniques, the vibration damping technique has the advantage of being non-destructive as well as highly sensitive for evaluating the interfacial region, and it can allow the materials industry to rapidly determine the mechanical properties of composites. In the present study, a simple optical system was contributed for measuring the damping factor of uniaxial fiber-reinforced polymer composites in the shape of cantilever beams. The interfacial damping factors in glass-fiber-reinforced epoxy resin composites were correlated with transverse tensile strength, which is a qualitative measurement of adhesion at the fiber–matrix interface. Four different composite systems were tested in this study. In each system, three different surface treatments of glass-fiber at three different volume fractions were evaluated. The experimental results show an inverse relationship between damping contributed by the interface and composite transverse tensile strength.

Correlation of fiber pull-out strength and interfacial vibration damping techniques by micromechanical analysis

Adhesion between fiber and matrix in fiber-reinforced polymer composites plays an important role both in controlling mechanical properties and in the overall performance of composites. This suggests that analytical and experimental methods to characterize the interface can be used to predict the mechanical performance of the material. To this end, vibration damping techniques have been used as a non-destructive method to evaluate interfacial effects on composites. According to the theory of energy dissipation, the quality of the interfacial adhesion can be evaluated upon separating the predicted internal energy dissipation associated with perfect adhesion from the measured internal energy dissipation of a composite system; this enables the quantification of interfacial adhesion. A micromechanics-based model for evaluating the adhesion between fiber and matrix from the damping characteristic of a cantilever beam was developed that shows an inverse relationship between the damping contributed by the interface and its adhesion strength. A simple optical system was used to measure the damping factor of unidirectional fiber-reinforced-polymer composites. Cantilever beam specimens containing either a single glass fiber or three types of single metallic wires embedded in an epoxy resin matrix were tested. A correlation was found between the measured interfacial adhesion strength directly from microbond pull-out tests and the micromechanics-based calculations from vibration damping experiments.

Non-destructive characterization of fibre-matrix adhesion in composites by vibration damping

Adhesion at the fibre-matrix interface in fibre-reinforced composites plays an important role in controlling the mechanical properties and overall performance of composites. Among the many available tests applicable to the composite interfaces, the vibration damping technique has the advantages of being non-destructive as well as highly sensitive. An optical system was set up to measure the damping tangent delta of a cantilever beam, and the damping data in glass fibre-reinforced epoxy-resin composites were correlated with transverse tensile strength which are also a qualitative measurement of adhesion at the fibre-matrix interface. Four different composite systems containing three different glass fibre surface treatments were tested and compared. Our experimental results showed an inverse relationship between damping contributed by the interface and composite transverse tensile strength.

Nondestructive Characterization of Fiber-Matrix Adhesion in Composites by Vibration Damping

Adhesion at fiber-matrix interface in fiber-reinforced composites plays an important role in controlling the mechanical properties and overall performance of composites. Among the many available tests applicable to the composite interfaces, vibration damping technique has the advantages of being nondestructive as well as highly sensitive. We set up an optical system to measure the damping tangent delta of a cantilever beam, and correlated the damping data in glass-fiber reinforced epoxy-resin composites with transverse tensile strength which is also a qualitative measurement of adhesion at fiber-matrix interface. Four different composite systems containing three different glass-fiber surface treatments were tested and compared. Our experimental results showed an inverse relationship between damping contributed by the interface and composite transverse tensile strength.