Fiber-matrix Interfacial Bond Strength Research Articles

Notch Tensile Strength of Carbon Fiber/Epoxy Composite Plate with a Center Hole under Static and Cyclic Loading

The tensile and fatigue properties of epoxy reinforced with 68 volume percent carbon fiber, CFRP, have been fully investigated. The effect of the presence of an open circular hole on tensile, fatigue residual strength, and fatigue strength of CFRP plates was studied experimentally and numerically. The results of pin bearing, i.e. bolt-loaded holes, tests were also investigated and evaluated. A three-dimensional orthotropic-elastic finite element code was developed to calculate the stress concentration factors of open circular holes or bolt-loaded holes in composite materials.The modulus of elasticity, tensile strength, and maximum elongation of CFRP are approximately equal to the values found in the technical data sheet of the supplier. A rule of mixtures type relation is adequate to predict the modulus of elasticity of such CFRP plate. This may be attributed to the high mechanical properties and high volumetric content of the fibers compared with the matrix, i.e. there is a marginal contribution of the strength of the matrix or the fiber-matrix interfacial bond strength. Based on the net stress analysis, there is no difference between the mechanical behavior of smooth and open-holed specimens, i.e. notch insensitivity. This is due to the incapability of the matrix to transfer the load from the discontinuous part. The same behavior was also found under cyclic loading. Due to the weakness in the bond between the fiber and matrix or in the shear strength of the matrix compared with the tensile strength of the fiber, the failure mode of all tested bolt-loaded unidirectional CFRP plates is shear-out. Further, the strength of such bolted joints is mainly dependent on the size of the contact area between the hole and the bolt.

Mechanical Characteristics and Terminological Behavior Study on Natural Fiber Nano reinforced Polymer Composite – A Review

Abstract In recent years, natural fibers with nano polymer composites are useful in the field of research, Engineering and Science as well it is used as an alternative reinforcement for conventional composite. Natural fibers are not only strong and light weight, but also relatively cheap and have properties like high specific strength, low weight, non-abrasive, eco-friendly and biodegradable. Generally used natural fibers like Jute, Sisal, Banana, Hemp, etc…, The reuse of waste natural fiber reinforcement of polymer is a sustainable option for the environment. The polymeric matrix materials along with suitable and proper filler and better filler/matrix create strong interaction between advanced and new methods or approaches. This enable to develop polymeric composites which shows great prospective applications in the construction of buildings, automotive, aerospace and packaging industries. Nano polymer composite shows considerable applications in different fields because of larger surface area, and greater aspect ratio, with fascinating properties. Being environmentally friendly, applications of nano polymer composites offer new technology and business opportunities for several sectors, such as aerospace, automotive, electronics, and biotechnology industries. Hybrid nano-polymer composites exploit the synergy between natural fibers in a nano-reinforced polymer-based composites. This leads to improve the properties along with the environmental appeal. The mechanical properties of a natural fiber reinforced nano polymer composite depend on parameters like fiber strength, fiber length, chemical treatment and orientation in addition to fiber-matrix interfacial bond strength. This review article aims at the clarification of the research and development in the improvement of mechanical properties of natural fiber reinforced polymer composites along with end applications.

Ageing of a thermosetting polyurethane and its pultruded carbon fiber plates subjected to seawater immersion

Carbon fiber reinforced polyurethane (CFRPU) composites exhibit a high potential in infrastructure application due to their efficient manufacturing and excellent mechanical properties. In the present article, the resistance to seawater immersion of a thermosetting polyurethane (PU) and its pultruded CFRPU plates was investigated, which was compared to a commonly used epoxy resin as well as its pultruded plate. The ageing conditions were determined as immersion in artificial seawater for one year at 20 °C, 40 °C or 60 °C. The water absorption/desorption, glass transition temperature (Tg), fiber-matrix interfacial bond strength and the tensile properties were evaluated as a function of time. As indicated by the water uptake testing, the PU resin exhibits a relative high water uptake (∼2.65%), while the CFRPU plates show a much lower value (∼0.71%), illustrating the good seawater resistance of the PU resin and the CFRPU. The positive resistance results were further supported by the high retention of the fiber-matrix interfacial bond strength and glass transition temperature for the immersed samples. In addition, the seawater immersion brings in a very slight decrease in the tensile strength for the PU and CFRPU plates. In terms of the above tested performances, the PU and CFRPU are significantly superior to the epoxy and carbon fiber reinforced plates. This result is attributed to the PU-carbon fiber adhesion of high resistance to the seawater.

Characteristics of Tension Softening of Polypropylene Fiber-Reinforced Lightweight Concrete

The purpose of this study is to determine the tension softening diagram and post-crack tensile strength of polypropylene fiber-reinforced lightweight concrete from bending tests and pull-out tests. Lightweight concrete has been actively applied in civil engineering applications, because the lightweight concrete is effective to reduce the dead load of structures and to improve the earthquake response of substructures. The addition of discontinuous fibers to cementitious materials drastically extends the toughness and strength of concrete. The tension softening diagram and fracture energy are important factors to analyze the mechanical behavior of concrete structures. And also, the post-crack tensile strength has been applied to predict the shear strength of fiber-reinforced concrete beams. In this study, the tension softening diagram and post-crack tensile strength of polypropylene fiber-reinforced lightweight concrete was determined by the bending test and the method based on the poly-linear approximation analysis. Furthermore, the post-crack tensile strength was clarified by the fiber-matrix interfacial bond strength obtained from the pull-out test.

Reduction in alkali–silica expansion due to steel microfibers

The alkali–silica reaction (ASR) produces an expansive gel that may cause cracking and displacement in concrete structures. Steel microfibers ranging from 1% to 7% by volume of cement mortar were incorporated to reduce the expansion and cracking. All specimens contained 5% of opal by weight of fine aggregates. The samples were cast and tested according to ASTM C-1260. A considerable reduction in expansion was observed for all steel microfiber-reinforced mortar specimens compared to the control specimens without fibers. The higher the fiber volume fraction, the lower the expansion. At constant fiber volume fraction, the expansion was further reduced when the curing time was extended from 1 day to 7 days due to an increase in the fiber-matrix interfacial bond strength.

Test Methods for Estimation of Interfacial Normal Strength in Unidirectional Fiber Reinforced Composites

In this work, two specimen geometries, namely, model single fiber composite and block specimen have been suggested for estimating the interfacial normal strength in unidirectional fiber reinforced composites. Analytical modeling of both the specimens has also been done to estimate the interfacial stresses in terms of constituent material properties. Finally, some failure criteria have been employed in conjunction with the experimental observations to estimate the normal bond strength of the interface. This methodology is applied to several fiber/matrix combinations with appropriate variations of the fiber-matrix interfacial bond strength. The results indicate good agreement between the two proposed specimen designs for estimating the normal strength of the strongly bonded interface.

Failure Modes in Unidirectional Composites under Transverse Loading

This paper reports on our attempts to demonstrate potential failure modes under combined thermal and transverse loading of unidirectional composites and to validate the predictions of an analytical model through careful design and testing of composite specimens. Several fiber/matrix combinations are being considered with appropriate variations of the fiber-matrix interfacial bond strength and processing conditions. The interfacial bond strength is reduced in one set of specimens by applying a release agent to the surface of the fiber prior to its incorporation in the matrix. Curing is done both at room and at elevated temperature to account for thermal residual stresses induced from the mismatch in the coefficients of thermal expansion of the constituents. The experimental technique including specimen preparation, test procedures and detection of the sequence of failure events is described. The correlation between the experimental and analytical results is fairly reasonable.

Processing and mechanical properties of AI2O3 fiber-reinforced NiAl composites

The mechanical properties of NiAl-matrix composites reinforced with 125-μm diameter single-crystal A12O3 (sapphire) fibers have been examined over the temperature range of 300 to 1200 K. Composites were fabricated with either a strong or weak fiber-matrix interfacial bond strength. During fabrication, a fiber-matrix interaction occurred such that fibers extracted from the NiAl matrix were fragmented and significantly weaker than the as-received fibers. Tensile results of the weakly bonded composite demonstrated that the composite stiffness was greater than the monolithic at both 300 and 1200 K in spite of the weak bond. Room-temperature strengths of the composite were greater than that of the monolithic but below rule-of-mixture predictions (even when the degraded fiber strengths were accounted for). At 1200 K, the ultimate strength of the composite was inferior to that of the monolithic primarily because of the poor fiber properties. No tensile data was obtained on the strongly bonded material because of the occurrence of matrix cracking during fabrication. Primarily because of the fiber strength loss, sapphire-NiAl composite mechanical properties are inferior to conventional high-temperature materials such as superalloys and are currently unsuitable for structural applications.

Fiber-Matrix Adhesion and Its Effect on Composite Mechanical Properties: IV. Mode I and Mode II Fracture Toughness of Graphite/Epoxy Composites

To optimize the level of fiber-matrix adhesion an understanding of the relationship between fiber-matrix interfacial bond strength and the mechanical and frac ture behavior of composites is essential. This study establishes the relationship between fiber-matrix interfacial shear strength (ISS) and interlaminar fracture toughness (both Mode I and Mode II) and failure modes for graphite/epoxy composites. A well defined and characterized graphite fiber/epoxy system was chosen in which the level of adhesion be tween fiber and matrix was changed by using the same graphite fibers with different sur face treatments. These surface treatments changed the level of adhesion between the fiber and matrix thus resulting in an increase of the fiber-matrix ISS by over a factor of two while the fiber and matrix properties remained unchanged. The Mode I and Mode II tests were conducted by the double cantilever beam (DCB) and end-notch flexure (ENF) tests methods, respectively. The Mode I fracture toughness ( GIC) of composites having low fiber-matrix ISS could not be determined from the DCB test because of extensive fiber bridging and crack meandering. For the composites having higher values of the ISS, the GIC increased with the ISS. The experimental results demonstrated that there is a strong dependency of Mode II fracture toughness ( GIIC) on fiber-matrix adhesion. Increased fiber-matrix adhesion in one group of composites significantly improved the GIIC , but the presence of brittle interphase around graphite fibers in another group of composites tended to cancel part of the improvement resulting from increased adhesion. Based on the major failure modes occurring during the Mode I and Mode II loading conditions, a causal link age between fiber-matrix adhesion and interlaminar fracture behavior of graphite/epoxy composites is established.