Metin Tanoğlu

The effects of glass-fiber sizings on the strength and energy absorption of the fiber/matrix interphase under high loading rates

The interphases of various sized E-glass-fiber/epoxy-amine systems were tested at displacement rates in the range 230–2450 μm/s by a new experimental technique (dynamic micro-debonding technique). By this method, the rate-dependent interphase properties, apparent shear strength and absorbed energies due to debonding and frictional sliding, were quantified. The systems include unsized, epoxy-amine compatible, and epoxy-amine incompatible glass fibers. The high displacement rates that induce high-strain-rate interphase loading were obtained by using the rapid expansion capability of piezoelectric actuators (PZT). The results of dynamic micro-debonding experiments showed that the values of interphase strength and specific absorbed energies varied in a manner that is dependent on the sizing and exhibited significant sensitivity to loading rates. The unsized fibers exhibit greater frictional sliding energies that could provide better ballistic resistance, while the compatible sized fibers show higher strength values that improve the structural integrity of the polymeric composites. In addition, significantly higher amounts of energy are absorbed within the frictional sliding regime compared to debonding. By using the experimental data obtained, a case study was performed to reveal the importance of the interphase related micro damage modes on energy absorption (and therefore ballistic performance) of glass/epoxy composite armor.

Investigating the effects of a polyester preforming binder on the mechanical and ballistic performance of E-glass fiber reinforced polyester composites

Abstract An experimental investigation was carried out to determine the effects of a preforming binder on the mechanical properties and ballistic performance of E-glass-fiber/polyester composite systems. The glass preforms were consolidated by application of heat and pressure over plies of the glass fabrics coated with various concentrations of a thermoplastic polyester binder. The peel strength of the preforms with various binder content was measured and the highest peel strength was obtained from preforms prepared with about 9 wt % of the binder. Composite laminates with and without binder were fabricated using VARTM technique and the effects of the binder on the composite mechanical properties were evaluated. It was found that the flexural strength and mode I interlaminar fracture toughness decreases by 15% and 40%, respectively, due to the presence of 3 wt % of the binder. Ballistic test was performed on E-glass/polyester composite panels using 1.1-g fragment-simulating projectiles and it was found that the binder amount has some considerable effect on the damage extension of the impacted composites. The results showed that the preforming binder has significant potential to tailor composite properties.

USE OF SILANE COUPLING AGENTS TO ENHANCE THE PERFORMANCE OF ADHESIVELY BONDED ALUMINA TO RESIN HYBRID COMPOSITES

Abstract Silane coupling agents were employed to improve the adhesion of vinyl-ester to alumina (Al2O3). Shear test by compression loading (ASTM D905) was used to study dry and wet adhesion. Scanning electron microscopy (SEM) was used to study the uniformity of silane coatings and the fracture modes after shear testing. Results showed that the adhesion and durability of the sandwiched alumina/vinyl-ester systems were significantly improved by certain silane surface treatment for most of the systems.

Effect of adhesive on the strengthening of aluminum foam-filled circular tubes

Studies of the crushing behavior of closed-cell, aluminum foam-filled aluminum and steel tubes have shown an interaction effect between tube wall and foam filler [1, 2, 3]. The crushing loads of foam-filled tubes are, therefore, found to be higher than the sum of the crushing loads of foam (alone) and tube (alone) mainly due to this effect. Santosa et al. [1], based on FEM results, proposed the following equation for the average crushing load of foam-filled square tubes of length b,

Investigation of properties of fiber/matrix interphase formed due to the glass fiber sizings

Sizings on glass fibers consist of a silane-based network that is chemically bound to the fiber and other compounds that are adsorbed onto the glass surface. Formation of interphase involves dissolution of adsorbed species and inter-diffusion of these compounds and resin monomers into the interphase region and chemical reaction of available functional groups. All these phenomena occur at the presence of the silane-based network. In this study, the effects of the silane-based network on the properties of the interphase region are investigated for an epoxy/amine resin system and compatible sized glass fibers. The composition of the sizing material bound to glass was determined using nuclear magnetic resonance (NMR) spectroscopy. Based on this information, model interphase materials were synthesized that were a blend of an epoxy/amine matrix and inclusions. The inclusions consist of an interpenetrating network of silane-based polymer and epoxy/amine thermoset that represents the interphase material formed during processing. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques were used to characterize the glass transition temperature and flexural modulus of the model materials. The properties of the model interphase material were obtained using the DMA results and established micromechanics models. The results show that the glass transition temperature of the model interphase is about −5°C, and its flexural storage modulus at room temperature is about 50% of that of the bulk matrix. This work has also shown that a reduction in the cross-link density of the bound network might significantly reduce the modulus within the interphase region by a factor of 5 to 8.

Effects of thermoplastic preforming binder on the properties of S2-glass fabric reinforced epoxy composites

Abstract The effect of a thermoplastic polyester binder on the thermophysical and mechanical properties of an S2-glass/epoxy–amine system was investigated. The purpose of the polymeric binder is to bond the individual fabric layers together during preforming prior to composite fabrication. This paper will address the significance of the binder chemistry, i.e., the compatibility of the binder with the matrix polymer, on the composite properties. The peel strength of preforms consolidated with various concentrations of binder was evaluated using the T-peel test. The highest peel resistance was obtained from preforms that have full coverage of the binder on the glass fabric. Further increase of the concentration of the binder does not change the peel strength. Scanning electron microscopy (SEM) on peel test fracture surfaces revealed mostly adhesive-type failure between binder and fiber. Double cantilever beam (DCB) and short beam shear (SBS) test results of the composite showed that the presence of about 2.6 wt% of the polyester binder reduces the Mode I interlaminar fracture toughness and apparent interlaminar shear strength of the S2-glass/SC-15 epoxy-amine system by about 60% and 25%, respectively. Moreover, the Tg of the matrix polymer within the interlaminar region decreases about 6°C due to the presence of the binder. The dissolution of the polyester binder within the reacting matrix resin is limited for the standard cure cycle.

A new technique to characterize the fiber/matrix interphase properties under high strain rates

Dynamic interphase-loading apparatus (DILA) has been developed to directly characterize the fiber/matrix interphase properties of composites under high loading rates. This apparatus uses a micro-mechanical method (micro-indentation) that is based on the debonding of a fiber from the matrix at the interphase region. Displacement rates up to 3000 μm/s that cause deformation of the interphase under high shear strain rates were obtained using the fast expansion capability of piezoelectric actuators (PZT). Transient force and fiber displacement for a specific displacement rate is measured during the test. The data are reduced to apparent average interphase shear strength and energy absorbed during debonding and frictional sliding during the micro-debonding process. An E-glass-fiber/epoxy-amine interphase was tested under various loading rates to demonstrate the capability of the test apparatus. Test results showed that the strength and energy-absorbing capability of the E-glass/epoxy-amine interphase are sensitive to loading rate.

Fiber/matrix interphase characterization using the dynamic interphase loading apparatus

The dynamic interphase loading apparatus (DILA) developed to perform microdebonding push-out tests directly characterizes the fiber/matrix interphase properties of composites as a function of loading rate. The use of a piezoelectric transducer allows one to input a variety of displacements and loading rates (quasi-static to 50 mm/s) to the indenter. Transient force and displacement values, recorded during the test, are then used to determine the average shear strength and energy absorbed during debonding and frictional sliding during the microdebonding process. An E-glass/vinyl ester composite was tested under single microdebonding as well as fatigue loading. Test results showed that the strength and energy-absorbing capability of the interphase was sensitive to loading rate.

Mechanical Behavior of Polypropylene-based Honeycomb-Core Composite Sandwich Structures

This article presents results from an experimental study, investigating the effects of core thickness on the mechanical properties of composite sandwich structures with polypropylene(PP)-based honeycomb core and glass fiber-reinforced polymer (GFRP) face-sheets fabricated by hand lay-up technique. Epoxy matrix and non-crimp glass fibers were used for the production of GFRP laminates. Flatwise compression (FC), edgewise compression (EC), three-point bending (3PB) and double cantilever beam (DCB) tests were performed to evaluate the mechanical behavior of the composite sandwich structures (CSSs). Based on the FC tests, an increase in the compressive modulus and strength was observed with an increase in the core thickness. For EC tests, peak loads up to crush of the sandwich panel is discussed using core thickness. According to the 3PB tests, a decrease in core shear stress and facesheet bending stress was observed as the core thickness increases.

Electrical and mechanical properties of superconducting MgB2/Mg metal matrix composites

MgB2/Mg composites were prepared using a metal matrix composite fabrication method that offers the potential to produce superconducting wires as an alternative approach to the powder in tube process. To obtain composites, MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical die under the pressure of 0.5 and 1.0 GPa for two hours at various temperatures. The x-ray diffraction technique was used for phase identification. Temperature dependence of resistivity and magnetization measurements were carried out to determine superconducting properties. The effects of composite fabrication temperature and the addition of the Mg on the mechanical properties of MgB2/Mg composites were investigated. For this purpose, the compressive mechanical testing was performed to measure the elastic modulus and fracture strength values of the composites. It was found that the relative weight fraction of the Mg and the fabrication conditions of the composites have considerable effect on the superconducting and mechanical properties of the composites.