The effect of interfacial adhesion on the tensile behavior of polystyrene–glass-bead composites

The tensile behavior at 20°C of polystyrene-glass-bead composites has been studied at several glass concentrations. To gain insight into the role of interfacial adhesion, the bonding between glass and polystyrene was varied by using different silane coupling agents. In contrast to the elastic behavior, the crazing behavior of the composites was found to be considerably affected by the degree of interfacial adhesion. This is explained by means of the different mechanisms for craze formation at adhering and nonadhering glass beads, respectively. Furthermore, it was found that both elastic and crazing behavior of the composites are influenced by the glass bead concentration.     

The morphology of fracture surfaces and mechanical properties of composites of polypropylene with glass fibers having different interface adhesion

For composites polypropylene–short glass fibers having different interface adhesion, correlation has been proved to exist between the morphology of fracture surfaces, the temperature dependence of impact strength, and the deformational and fracture behavior in tensile loading. The results are interpreted in terms of the mechanism of distortion plasticity for unfilled PP and for filled PP having weak interface adhesion, and on the basis of dilatation plasticity for filled polypropylene with a higher interface adhesion. The transition from the distortion to the dilatation mechanism can be seen in fracture surfaces after tensile destruction in composites possessing a higher interface adhesion.     

Dynamic mechanical analysis of the effect of water on glass bead–epoxy composites

Dynamic mechanical analysis (DMA) has been used to investigate the effect of water and glass bead surface treatment on the properties of glass bead–epoxy composites. By treating or not treating the glass beads with a silane coupling agent, we fabricated composites with ostensibly good or poor interfacial adhesion. SEM images of fracture surfaces and water uptake data confirmed this picture. We used dynamic mechanical tests to measure the material properties of dry and wet specimens. Temperature sweep tests of atmosphere-conditioned specimens indicated that the value of the loss tangent at the temperature of the α-α-relaxation peak was most sensitive to interfacial adhesion. For wet specimens, the magnitude of an additional relaxation process, denoted as the ω-relaxation, correlated strongly with water uptake and, indirectly, interfacial adhesion. Master curves constructed from frequency sweep tests also manifested differences among dry and wet specimens, but shift factor data suggested that these tests were more prone to complications due to water loss. Apparent activation energies of α- and β-relaxation processes were statistically significant indicators of interfacial adhesion in dry and wet composites, respectively. © 1996 John Wiley & Sons, Inc.     

Effects of interfacial adhesion on microdamage and rheological behaviour of glass bead filled nylon 6

Model composites consisting of glass beads dispersed in a matrix of nylon 6 with different degrees of interfacial adhesion were prepared. The effects of interfacial adhesion on damage generation in the glass bead filled nylon 6 were studied by acoustic emission monitoring and scanning electron microscopy, and the critical damage stress was measured. Improvement of the interfacial adhesion enhanced the tensile strength of the composite. The melt rheological behaviour of the glass bead filled nylon 6 was also investigated. It was found that the interfacial adhesion strength significantly affected the rheological behaviour of the glass bead filled nylon 6.     

Fracture behavior of glass bead filled epoxies: Cleaning process of glass beads

Inorganic particles are commonly cleaned with solvents such as alcohols before being incorporated into thermoset polymers as fillers or tougheners, but the role of the cleaning process has never been examined. In this study, the effect of the cleaning process on the fracture behavior of particulate composites is investigated using glass bead filled epoxies as model systems. The cleaning process is shown to be a simple method to strengthen the interface between the glass beads and the epoxy matrix. Although the chemistry of the glass bead surface is unlikely to be altered by the cleaning process, submicron particles that exist on the glass bead surfaces are removed by cleaning with distilled water or ultrasonic vibration. The removal of submicron particles increases the interfacial strength between the glass beads and the matrix and changes the tensile strength of the composites. However, the modulus and fracture toughness of the composites is not significantly dependent on the cleaning process. Thus, it may be the case that debonding of the glass beads is not one of the major energy dissipating mechanisms in the fracture of glass bead filled thermoset systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1371–1383, 2001     

Physical aging in particulate-filled composites with an amorphous glassy matrix

Physical aging was studied on particulate -filled glassy network polymers by means of mechanical -dilatational, differential scanning calorimetry (DSC) and density measurements on specimens that were aged at room temperature. The composites aged for 0.5 day fractured in a brittle manner at a constant ultimate stress, which is close to the tensile strength of the unfilled material, regardless of the filler content and the presence of a coupling agent. This type of mechanical behavior is caused by the compressive residual stresses that are present due to curing and differential thermal shrinkage. As aging takes place, the compressive residual stresses are relieved; as a result the ultimate tensile strengths of the composites decrease. The 120 -day -old untreated glass bead containing composites exhibited dilatation and yield in mechanical -dilatational testing. This type of behavior is described as “having no adhesion” between the filler and the matrix. The 120 -day -old composites with coupling agent -treated glass beads fractured at a tensile stress which is equal to 1/1.6 the tensile strength of the unfilled material. These materials did not exhibit dilatation and yield in mechanical -dilatational testing. Density and DSC data indicate densification and enthalpy relaxation upon again and support the hypothesis presented for the observed change in the mechanical -dilatational behavior.     

Failure mechanisms in polypropylene with glass beads

The effect of glass beads on the stress-strain behavior of isotactic polypropylene has been examined. Poisson's ratio and secant compliance as a function of strain have been measured. Both sets of data are consistent with interfacial debonding as the initial damage mechanism. Interfacial debonding is then followed by extensive plastic yielding of the matrix at the debond sites. The maximum stress and strain to failure decrease with glass bead content and glass bead diameter. Impact properties correlate with the ability of the composites to reach high strain to failure. The proposed failure mechanisms are supported by fractography and in-situ deformation studies by scanning electron microscopy.     

Unexpected behavior between polystyrene and untreated and silane‐treated glass beads in filled polymeric composites

Attempting to extend the database of work reported earlier, the practical adhesion between a glass filler, modified by various silane‐coupling agents, and a polystyrene matrix is measured and compared with predictions based on a generalized thermodynamic criterion. Measurements leading to adhesion failure are carried out using the single‐particle composite method, in which a rectangular polymer specimen containing a single untreated or silane‐treated glass bead is subjected to increasing uniaxial tensile stress until interfacial failure, as observed using a microscope, occurs at one of the poles of the sphere. The results show no difference in adhesion strength between an untreated and a silane‐treated glass bead, and the interfacial failure mechanism for the polystyrene composites is markedly different from that observed for previously studied systems. Crazes originate at the particle pole at low values of the applied stress and continue to form along the interface with continued strain. A dye test performed on filled composites confirms that the polystyrene is not wetting the untreated glass beads. More studies must be done to determine the origin of the anomalous failure and wetting behavior. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 521–526, 2003     

Investigation of deformation mechanism in polypropylene/glass fiber composite

A great amount of work has been done over the past few years to understand the structure–properties relationship in polypropylene/glass fiber composites. This is because of the very fast‐growing rate of polypropylene applications in the automotive and other industries. This work focused on the role of glass fibers and fiber–matrix adhesion on deformation mechanism. Composites with different fiber content, with and without adhesion promoter, were fabricated. Tensile tests and microscopy techniques were conducted. Based on the results, a physical model has been proposed that illustrates the initiation and growth of the damage under static loading condition. According to this work, the introduction of glass fibers shifts the deformation mechanism from shear yielding to crazing. Although crazes propagate in a different manner in composites containing standard and treated fibers, no influence of interfacial adhesion was observed on craze thickening phenomenon. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2171–2176, 2003     

The properties of dry-spun carbon nanotube fibers and their interfacial shear strength in an epoxy composite

Continuous fibers composed of carbon nanotubes have been adopted as reinforcements for polymeric composites. This paper presents several fundamental studies relevant to the mechanical behavior of CNT fibers, including fiber tensile behavior; in situ SEM observation of fiber deformation mechanisms; and fiber modulus, ultimate strength and fracture strain measurements. A modified Weibull strength distribution model that takes into account the flaw density variation with fiber diameter has been adopted for the statistical strength analysis. The interfacial shear strength between the carbon nanotube fiber and the epoxy matrix has been measured using fragmentation tests of single-fiber composites.     

Influence of morphology on rheological and mechanical properties of SEBS-toughened,glass-bead-filled isotactic polypropene

The influence of morphology of glass-bead-filled isotactic polypropene containing 0–20 vol% thermoplastic elastomers (TPE) on mechanical and rheological properties was investigated. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene(SEBS) and the corresponding block copolymer grafted with maleic anhydrid (SEBS-g-MA) were used as thermoplastic elastomers, realizing, in the first case, a three-phase morphology with separately dispersed glass beads and SEBS particles. In the second case, SEBS-g-MA forms an elastomeric interlayer between glass beads and polypropene matrix, comprising core–shell particles. Young's modulus and tensile yield stress of the hybrid composites decrease with an increase in TPE volume fraction due to low stiffness and strength of TPE. In comparison with the three-phase morphology of hybrid composites with SEBS, SEBS-g-MA interlayers effect a reduced stiffness of the hybrid composites but improve interfacial adhesion and, thus, tensile yield stress. Rheological storage and loss moduli increase with an increase in glass bead and TPE volume fraction. Due to improved interfacial adhesion, melt elasticity and viscosity are enhanced by the SEBS-g-MA interlayer when compared with separately dispersed SEBS. Consequently, the reduced stiffening effect of the glass beads due to SEBS-g-MA interlayer decreases mechanical elasticity, whereas improved interfacial adhesion, also promoted by the SEBS-g-MA interlayer, enhances tensile yield stress and melt elasticity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2499–2506, 1998     

Effects of moisture absorption on mechanical and viscoelastic properties in liquid thermoplastic resin/carbon fiber composites

This article investigated the effect of moisture on the tensile strength and in‐plane shear of laminated composites. For this, the results of a composite system based on a new thermoplastic Elium® 150 resin were compared to a traditional epoxy resin result. Both composites were fabricated via VARTM using a 0/90° plain weave carbon fiber fabric. For the non‐conditioned specimens, the thermoplastic composites presented 30% more tensile resistance in comparison to epoxy composites. For conditioned specimens, this difference was 14%. These results were related to plasticization, which tends to favor the polymer softening providing a greater matrix plastic deformation, promoting a ductile fracture of the composite. On the other hand, the in‐plane shear properties were 30% higher for the thermosetting laminates for both conditions. In this case, moisture may have favored the formation of surface cracks and weakened the fiber/matrix interfacial adhesion. Additional analysis based on design of experiments has shown that the Elium® 150 resin significantly affects all responses and presented in fact a better behavior in comparison to Epoxy resin. While the conditioning effects have featured a statistically noticeable contribution to the tensile strength, the presence of the moisture did not provide a significant enhancement to the in‐plane shear strength. Besides that, the unknown fractographic aspects of the fracture surfaces of both composites were used as a complementary tool for the mechanical characterization. POLYM. ENG. SCI., 59:2185–2194, 2019. © 2019 Society of Plastics Engineers     

Fracture behavior of glass bead-filled poly(oxymethylene) injection moldings

The mechanical properties of glass bead filled poly(oxymethylene) were investigated as a function of glass bead content and glass bead diameter using injection molded test pieces. Fracture toughness measurements were made using single edge-notched tension and single edge-notched bend specimens. The effect of notch orientation with respect to the mold fill direction on fracture toughness was studied using single gate and double gate moldings. Tensile strength and flexural modulus were measured using standard test pieces. It was found that; (i) fracture toughness of the filled and unfilled polymer was relatively independent of notch orientation, (ii) the presence of weldlines in the molded test pieces did not affect the fracture toughness of unfilled polymer or its composites, (iii) fracture toughness of filled polymer was always considerably lower than that of the unfilled polymer; fracture toughness decreased sharply with increasing bead concentration, (iv) fracture toughness was not a sensitive function of glass bead diameter; it decreased slightly as bead diameter increased, (v) strain energy release rate as measured under impact decreased with increasing bead concentration, (vi) tensile strength decreased linearly with increasing glass bead concentration and was inversely proportional to the square root of the bead diameter, (vii) weldlines did not affect the tensile strength of the polymer or its composities, (viii) flexural modulus increased linearly with increasing glass bead concentration according to the Einstein equation.     

Some mechanical properties of particulate-filled thermosetting and thermoplastic polymers

A semiempirical, single-parameter equation describes the modulus of particulate systems This equation has been found applicable for thermoplastic/glass bead systems, and it is further verified for particulate thermosetting systems (epoxy and polyester matrices). The temperature effect on the modulus of epoxy/glass bead composites is also analyzed. Crazing characteristics calculated from tensile data of thermoplastic/glass bead composites are summarized and compared with literature results on the corresponding unfilled polymers. The effect of coupling agents and preliminary results on rigid foams are also presented.     

Experimental analysis and theoretical modeling of the mechanical behavior of short glass fiber and short carbon fiber reinforced polycarbonate hybrid composites

In this research, polycarbonate (PC) composites with short glass fiber (SGF) and short carbon fiber (SCF) hybrid fiber reinforcements were compounded by single screw extruder and specimens were prepared by injection molding machine. This article aims to investigate the mechanical properties of PC hybrid composites, by means of the experimental and the theoretical methods. The composites were subjected to tensile test. Experimental results showed the improvements in tensile strength and modulus by increasing the SCF content of the hybrid composite. The theoretical tensile strength was predicted based on Kelly–Tyson model and rule of hybrid mixture. Kelly–Tyson model showed to be a good approximation to predict the tensile strength of composite. When the SCF was replaced by milled carbon fiber (MCF) to form a PC/SGF/MCF hybrid system, poorer mechanical properties are reported due to the weaker interfacial adhesion between MCF and PC, as proven by the scanning electron microscopy. POLYM. COMPOS., 37:1238–1248, 2016. © 2014 Society of Plastics Engineers     

Concentration effect of γ‐glycidoxypropyltrimethoxysilane on the mechanical properties of glass fiber–epoxy composites

In this study, glass fibers were modified using γ‐glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of γ‐glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short‐beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three‐point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat‐cleaned glass fiber reinforced composite is enhanced by ∼59% as a result of the glass fiber treatment with 0.5% γ‐GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% γ‐GPS treatment of glass fibers was observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Fiber-stretching test: a new technique for characterizing the fiber–matrix interface using direct observation of crack initiation and propagation

A new micromechanical technique for experimental determination of fiber-matrix interfacial properties is presented. This technique consists in tensile loading of the fiber, with a matrix droplet on it, at both ends, accompanied by continuous direct observation of interfacial crack propagation. In comparison with the well-known microbond test, the new method has two important advantages. First, crack propagation is stable for any embedded fiber length and any relation between adhesion and friction at the interface. Second, compliance of the test equipment does not affect the results, and specimens with long free fiber ends can be successfully tested. A similar result can be reached using the pull-out or microbond test with an 'infinite' (very long) embedded fiber length. An algorithm for separate determination of the interfacial adhesion and friction from experimental relationships between the crack length and applied load is described. The new test was employed to determine the interfacial parameters for composites of glass fibers with polypropylene, polystyrene, and polycarbonate. For each fiber-polymer system investigated, the following parameters were calculated: ultimate interfacial shear strength; critical energy release rate for crack propagation; and adhesional pressure. Our approach to the estimation of the work of adhesion, WA, from micromechanical tests, based on the concept of adhesional pressure, allowed us to calculate the WA values for several thermoplastic matrix-glass fiber pairs and to obtain values consistent with previous estimations made according to other approaches.     

The Melt Flow Properties of Poly(propylene)/Glass Bead Composites

The effects of filler content and its surface treatment on the melt flow properties of A‐glass bead‐filled poly(propylene) (PP) composites have been investigated using a capillary rheometer at a wide apparent shear rate scope of 150 to 7 200 s^–1 and a temperature range of 160 to 200°C. It was found that the melt shear flow obeyed roughly the power law. The melt shear viscosity (η_w) of the treated glass bead‐filled system with a silane coupling agent was somewhat higher than that of the raw glass bead‐filled system when both the systems were subjected to the same test conditions. The increase of the resistance to flow and flow satiability for the former system can be attributed to the improvement of the compatibility and interfacial adhesion between the filler and matrix as well as the dispersion of the filler in the matrix due to the surface treatment of the glass beads. The dependence of η_w on temperatures can be expressed with an Arrhenius relationship. The temperature sensitivity of η_w for the composite melts is greater than that of the unfilled PP. Furthermore, η_w increases obviously with the volume fraction (ϕ_f) of the fillers at lower shear rates, while the dependence of η_w on ϕ_f decreases with the increase of shear rates. This is attributable to the increase of the ability of relative movement between the filler and matrix melt at high extrusion rates.     

Acoustic emission in single filament carbon/polycarbonate and Kevlar®/olycarbonate composites under tensile deformation

An analysis of envelope signals of acoustic emission (AE) produced from carbon/polycarbonate and Kevlar®/polycarbonate composites undergoing tensile deformation has been carried out to identify the sources of emission. The Kaiser effect was reproduced to validate the AE technique. Two different fiber failure mechanisms, i.e., fiber fracture and fiber degradation in Kevlar®/polycarbonate composite have been identified. A one-to-one correspondence between acoustic emission signals and fiber fracture and degradation has been established. It is shown that the critical length of the fiber, evaluated by using acoustic emission signals, is helpful in understanding the fracture behavior of the composites, as affected by surface treatments of the fibers.     

Physico-Chemical and micromechanical analysis of the interface in a poly(phenylene sulfide)/glass fiber composite—a microbond study

The glass fiber/PPS composite has excellent thermal and chemical properties. The main disadvantage of the composite is its poor mechanical resistance to impact. To improve this property, the fibers were coated with a new type of sizing. The equired characteristics for this sizing is to create strong interactions between the PPS matrix and the glass fiber surface. The ability of the sizings to improve the glass/PPS adhesion has been assessed by the microbond technique. An inconvenience of this technique is the difficulty in defining a parameter that is characteristic of the interfacial adhesion. The objective of this publication is to demonstrate that a plastic flow of the PPS matrix around the fiber leads to a uniform shear strength. The adhesion between these two materials can therefore be obtained by the mean interfacial shear strength.