Modulus Of Epoxy Research Articles

4-Point beam tensile test on a soft adhesive

An adhesive butt joint with a soft bondline has been studied. A series of experiments was conducted on test pieces constituted of aluminium adherends bonded with a low modulus epoxy adhesive, Scotch Weld™ 2216. The joint was subjected to four point bending, in tension/compression loading, under constant deflection rate, with the bondline being parallel to the applied load. The objective was to examine and evaluate crack nucleation for a range of adhesive layer thicknesses. Three criteria were used to evaluate joint efficiency. Firstly, force/stress at crack onset revealed that thinner bondlines were preferable to produce stronger and stiffer bonded structures. Secondly, fracture energy was derived, which, in the present configuration, is associated with the energy stored within the adhesive layer, rather than the substrates. This is one of originalities of the test proposed. Fracture energy data lead to the conclusion, that more energy is dissipated by the joints with lower effective rigidity, viz. thicker bondlines. Finally, we applied a criterion of non-linear, ‘pragmatic’ work of adhesion – similar to the J-integral approach. In terms of energy consumption, the third criterion yielded (quasi) independence of the adhesive thickness. From the data collected, we conclude that for optimal joint design, rate effects must be carefully taken into account.

A Micro-Mechanical Model for Elastic Modulus of Multi-Walled Carbon Nanotube/Epoxy Resin Composites

Multi-walled carbon nanotube (MWCNT) powder was used as reinforcement in epoxy resin with weight percentages 0.5, 1, 2 and 3% respectively. Dispersion of MWCNTs in the epoxy resin was obtained by a three mill rolling process. Tensile strength, compressive strength and elastic modulus were obtained from load versus displacement results. A theoretical model was developed to calculate the elastic modulus and compare with the experimental results. There was a similar trend in the experimentally obtained elastic modulus and in a modified Halpin-Tsai theory. Results show that the tensile strength, compressive strength and elastic modulus of epoxy resin are increased with the increasing of percentage of MWCNT fillers. The significant improvements in tensile strength, compressive strength and elastic modulus were attributed to the excellent dispersion of MWCNT filler in the epoxy resin.

Modeling and mechanical performance of carbon nanotube/epoxy resin composites

The effect of multi-walled carbon nanotube (MWCNT) addition on mechanical properties of epoxy resin was investigated to obtain the tensile strength, compressive strength and Young’s modulus from load versus displacement graphs. The result shows that the tensile strength, compressive strength and Young’s modulus of epoxy resin were increased with the addition of MWCNT fillers. The significant improvements in tensile strength, compressive strength and Young’s modulus were obtained due to the excellent dispersion of MWCNT fillers in the epoxy resin. The dispersion of MWCNT fillers in epoxy resin was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis.Also, Halpin–Tsai model was modified by considering the average diameter of internal/external of multi-walled nanotube and orientation factor (α) to calculate the Young’s modulus of multi-walled carbon nanotubes (MWCNTs)/epoxy resin composite. There was a good correlation between the experimentally obtained Young’s modulus and modified Halpin–Tsai model.

Fabrication, Structure and Properties of Epoxy/Metal Nanocomposites

AbstractGd2O3 nanoparticles surface‐modified with IPDI were compounded with epoxy. IPDI provided an anchor into the porous Gd2O3 surface and a bridge into the matrix, thus creating strong bonds between matrix and Gd2O3. 1.7 vol.‐% Gd2O3 increased the Young's modulus of epoxy by 16–19%; the surface‐modified Gd2O3 nanoparticles improved the critical strain energy release rate by 64.3% as compared to 26.4% produced by the unmodified nanoparticles. The X‐ray shielding efficiency of neat epoxy was enhanced by 300–360%, independent of the interface modification. Interface debonding consumes energy and leads to crack pinning and matrix shear banding; most fracture energy is consumed by matrix shear banding as shown by the large number of ridges on the fracture surface. magnified image

Prediction of Mechanical Properties of Mica-filled Epoxy Composite Using Various Mechanical Models

This paper reports an investigation on the prediction of tensile properties of mica-filled epoxy composites. Various mechanical models were used to predict the tensile properties of mica-filled epoxy composites at several mica concentrations (5-30 vol%). The tensile properties of mica-filled epoxy at various mica contents were determined experimentally and modeled using Nielsen, Nicolais-Narkis, Verbeek, Halpin-Tsai, Guth, and Novak models. It was found that the tensile modulus of epoxy increases with increasing mica content, whereas the elongation at break and tensile strength decrease. Predictions, which have been offered by the models on tensile strength, elongation at break, and Young’s modulus, are in good agreement with experimental data over the range of mica contents studied. The Halpin-Tsai model shows best agreement in predicting the Young’s modulus (accuracy > 93 %), and Novak curve fitting shows best prediction for elongation at break (accuracy > 99%) for mica-filled composites. In the case of tensile strength, good agreement with Nicolais-Narkis models (accuracy > 99%) was obtained.

Data reduction methodologies for single fibre fragmentation test: Role of the interface and interphase

The single fibre fragmentation test (SFFT) is commonly used to characterise the fibre/matrix adhesion. In order to quantify the fibre/matrix adhesion the cumulative stress transfer function (CSTF) methodology was developed so that the elastoplasticity of the matrix could be included in the analysis through the plasticity-effect model [Tripathi D, Chen F, Jones FR. A comprehensive model to predict the stress fields in a single fibre composite. J Comp Mater 1996;30;1514–38., Tripathi D, Jones FR. Measurement of the load-bearing capability of the fibre/matrix interface by single fibre fragmentation. Comp Sci Technol 1997;57:925–35.] The limitations of this technique for the data reduction have been addressed by the use of the Plasticity Model to input the non-linearity of the matrix into methodology for fragmentation of a fibre in a matrix. An improved methodology, known as the revised cumulative stress transfer function (RCSTF) is described. The adhesion of a nanoscale plasma copolymer coated glass/epoxy system has been used to examine this approach to the fragmentation process. This methodology is also extended to account for the presence of an interphase. To validate the three phase model, carbon fibre coated with high and medium modulus epoxy resin were used to simulate fibre/interphase/matrix.

Electrospun Polymer/MWCNTs Nanofiber Reinforced Composites “Improvement of Interfacial Bonding by Surface Modified Nanofibers”

AbstractIn-house synthesized copolymers Polystyrene-co-glycidyl methacrylate (PSt-co-GMA) are electrospun as mat of surface modified nanofibers with and without multi walled carbon nanotubes (MWCNTs). Composites are then formed by embedding layers of the nanofiber mats into epoxy resin. Interfacial bonding between polymer matrix and the nanofibers, and surface modification driven enhancement in mechanical response is assessed under flexural loads. Results indicate that at elevated temperture storage modulus of epoxy reinforced by PSt-co-GMA nanofibers and PSt-co-GMA/ MWCNTs composite nanofibers is about 10 and 20 times higher than the neat epoxy, respectively, despite weight fraction of the nanofibers being as low as 2%. Interfacial interaction is revealed by the storage modulus comparison of unmodified Polystyrene (PSt) and modified PSt-co-GMA nanofiber reinforced composite. To enhance further the resulting “crosslinked” structure, crosslinking agent ethylenediamine is also sprayed on the nanofibrous mats. Increased crosslinking density improves mechanical response of sprayed-over PSt-co-GMA nanofibers reinforced composites which is about 4 times higher than plain PSt-co-GMA nanofibers.

Stress failure of airborne optical assembly resulting from rigid, high modulus epoxy adhesive and quality improvements

AbstractUp to 40% failure odds on an airborne optical assembly were found during finalizing the design‐production phase. It resulted in lens splitting, cracking, and shattering. The combined stress of residual stress originated from solidification shrinkage and deformation stress and from temperature changes that drastically caused the failures. The optical assembly was composed of aluminum shell, rigid epoxy adhesive layer, and glass lens. Mechanism and affecting factors of the failure were investigated on process, operation, and materials. A series of comparative trail experiments were carried out. It was recommended to prevent the failures by redesigning match clearance between duralumin wall and lens, replacing rigid epoxy adhesive with flexible polyurethane adhesive. Via these new measures, all optical assemblies made hereafter succeeded and passed all military environmental tests and inspections, with a zero percent failure odds. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 45–51, 2006

Relation between shear yield strength at the fiber-matrix interphase and Young's modulus of epoxy resin

(2000). Relation between shear yield strength at the fiber-matrix interphase and Young's modulus of epoxy resin. Composite Interfaces: Vol. 7, No. 5-6, pp. 487-495.

Effects of Young's modulus of epoxy resin on axial compressive strength of carbon fibre

Using epoxy resins with various molecular weight between cross-linkings, attempts have been made to estimate the fibre axial compressive strength of pitch-based graphitized fibre, and the effect of Young's modulus of epoxy resins on compressive strength was investigated. The estimated compressive strength of fibre decreases with increasing temperature. This decrease in compressive strength may be accounted for by a decrease in the radial compressing force due to a decrease in the residual thermal stress. There is a linear relationship between the estimated compressive strength and radial compressive force in a temperature range from room temperature to 80 °C. The estimated compressive strength of the fibre increases with increasing Young's modulus of epoxy resins. In order to realize reinforcing fibres with a higher compressive strength, it will be necessary to use a resin matrix with a higher modulus.

A study on compressive strength of unidirectional graphite-epoxy composites

The shear moduli of the unidirectional graphite-epoxy composites and the matrix material 'epoxy' under compressive load were measured by torsion tests. The compressive failure tests were also carried out and the acoustic emission was measured. The shear modulus of epoxy did not decrease until a high compressive strain was applied. Therefore, the previous theories for the compressive strength which require the decrease of shear modulus of epoxy under the compressive stress should be questioned. Young's modulus and the shear modulus of composites suddenly decreased at a load about 10-20% lower than the compressive fracture load, and the numbers of events of acoustic emission rapidly increased. Scanning electron micrographs have shown that the section of the failed fiber is skewed and stepwise, (characteristics different from those of the tensile fracture). The stresses caused by the difference between Poisson's ratio of the fiber and that of the matrix under a compressive load and the thermal residual stres...

Prediction of residual stress in LSI plastic packages by thermoviscoelastic analysis for a 3-layer laminated beam.

Fundamental equations based on the linear-thermoviscoelastic theory were established to obtain the temperature and residual stress by cooling in a 3-layer laminated beam. The transient thermal stress and deformation in the laminated beam made of composite materials constructed LSI plastic packages were calculated using these fundamental equations. It was found that the residual stress is strongly related to glass transition temperature and Young's modulus of epoxy resins, and the material design method necessary in order to decrease the residual stress was clarified.