Fatigue of glass laminates subjected to repetitive impact loading

Fatigue characteristics obtained for repetitive impact tensile loading in a DSO impact tester are presented for a glass-reinforced Textolite. There are differences in the fatigue life, temperature rise, and the variation of the elastic properties as compared with the case of repetitive sinusoidal stress cycles. The effect of the geometry of the test piece gage length on the measured parameters is examined and methods of predicting fatigue life are discussed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 751–754, July–August, 1969.     

Fatigue performance of glass/polyester laminates and the monitoring of material degradation

Experiments are performed on glass/polyester composites under fatigue loading. The stiffness degradation is recorded as an indirect measure of material damage. The stiffness decrease rate is described by a power dependence on stress; this relationship allows the fatigue law to be derived. Stiffness-controlled fatigue curves are generated and presented in an S-N-diagram based on normalized stress (equivalent to strain). Such stiffness controlled fatigue curves can be used as a basis for design criteria for components.Presented at the 9th International Conference on Mechanics of Composite Materials, 17–20 October 1995, Riga, Latvia.Materials Department, Risø National Laboratory, Roskilde, Denmark. Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 1, pp. 32–41, January–February, 1996.     

Interlaminar fracture of multidirectional glass/epoxy laminates under mixed-mode I + II loading

The mixed-mode I + II interlaminar fracture of multidirectional glass/epoxy laminates is investigated. Mixed-mode bending (MMB) tests were performed on specimens with delaminations in 0/θ-type interfaces, with θ varying from 0 to 90°. Preliminary three-dimensional finite-element analyses validated the beam theory model (BTM) used for analysing experimental data. The compliances measured are in a good agreement with BTM predictions. The total critical energy release rate G_c varies linearly with the mode II ratio G_II/G, although some discrepancies are observed in the high-mode II results for the 0/45 and 0/90 specimens. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 3, pp. 349–366, May–June, 2007.     

Cylindrical bending responses of angle-ply piezoelectric laminates with viscoelastic interfaces

The time-dependent behavior of a simply supported, angle-ply piezoelectric laminate in cylindrical bending with viscoelastic interfaces is investigated. The interfacial bonding in piezoelectric laminates is considered to be dielectrically weakly (or highly) conducting, and mechanically compliant characterized by the Kelvin–Voigt viscoelastic law. The state-space approach, which is directly based on the piezoelectricity equations and very effective in analyzing laminated structures, is employed. For exact analysis, a state equation of the relative sliding displacements with respect to the time variable is further presented. Comparison study shows that the numerical results by the present analysis agree well with those reported before. Numerical results also indicate that the electromechanical response of the piezoelectric laminates with viscoelastic interfaces changes remarkably with time elapsing. Thus, the bonding imperfection should be considered carefully in the practical design of piezoelectric laminates.     

Deformation behavior and strength of unidirectional carbon fiber laminates

The elastic deformation behavior and the load-carrying capacity of unidirectional carbon fiber laminates under static loading at room and cryogenic (down to 77 K) temperatures are investigated. The possible ways of predicting their elastic and strength characteristics proceeding from the volume content and mechanical parameters of fibers and matrix are analyzed. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 583–598, September–October, 2006.     

Relation between the structural and strength characteristics of textolite glass laminates

The authors derive approximate relations between the microstructure parameters of densely reinforced textolite glass laminates and the static strength and fatigue life of the material. The relations obtained are compared with the results of experiments performed on materials with varying degrees of crimping of the filaments and varying densities of the cloth reinforcement.Mekhanika Polimerov, Vol. 3, No. 2, pp. 302–308, 1967     

Concerning the glass fiber strength distribution function

The statistical strength distribution functions of glass monofilaments of various composition are considered. On the basis of the experimental data it is shown that the fiber strength distributions can be described by a three-parameter function of the Weibull type.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fibers, Moscow Regions. Translated from Mekhanika Polimerov, No. 1, pp. 131–136, January–February, 1970.     

Multiple cracking in carbon/epoxy laminates and pre-stressing of fibers

The multiple cracking of laminates with brittle plies can be suppressed by prestraining in tension of the fibers in the ductile plies. Experiments with tensile loading, acoustic emission, and crack counting demonstrate that such multiple cracking can be delayed and thus higher working strains can be allowed (without multiple cracking) for such laminates. In [0°/±65°/0°] laminates the strain for crack initiation can be increased from about 9.9% (for no prestrain) to above 1.4% (for 0.8% prestrain).Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga. October, 1995.Materials Department, Risøe National Laboratory, Roskilde, Denmark. Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 350–362, May–June, 1996.     

Moisture absorption and mechanical and acoustic responses in shear of a glass fiber fabric/epoxy resin composite

An analysis of the mechanical and acoustic responses of a laminate composed of 12 layers of glass fiber fabric/epoxy resin and conditioned in environments with relative humidities of 0, 60, and 96% RH at 60°C is presented. The first part of the study consists in following the weight gain according to the duration of hygrothermal conditioning, and the second part—in test ing 45°-oriented specimens in uniaxial tension up to failure at constant imposed displacement rates, with registrating the acoustic emission to track the damage process. The influence of moisture content in the material showed up as a significant decrease in its shear modulus, shear stress, and acoustic emission with growing quantity of absorbed water. An exponential function is proposed for describing the relationship between the varying shear modulus and the shear strain. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 595–602, September–October, 2007.     

Effect of low-speed impact damage on the buckling properties of E-glass/epoxy laminates

The postimpact buck ling loads of E-glass/epoxy laminates have been measured. Composite samples with the stacking sequence [+45/−45/90/0]_2s were subjected to low-speed impact loadings at various energy levels. The tests were conducted on a specially developed vertical drop-weight testing machine. The main impact parameters, such as the peak load, absorbed energy, deflection at the peak load, and damage area, were evaluated and com pared. The damaged specimens were subjected to compressive axial forces, and their buckling loads were determined. The relation between the level of impact energy and buck ling loads is investigated.     

Numerical aspects on computational homogenization of epoxy/glass composites

Numerical aspects of two-scale modeling of epoxy/glass composites are presented. The homogenization process is carried out under consideration of periodic boundary constraints (PBC) of the representative volume element (RVE) due to the periodic structure of glassfiber reinforced epoxy systems. The introduction of artificial constraints for computing macro-stresses and macro-moduli is presented by giving the modified algorithmic treatment of a two-scale approach using PBC. The proposed algorithm is applied to an ISO 527 epoxy/glass test specimen. The results of computations considering or not considering interphases and interfaces within the composite are compared. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Water absorption and swelling of glass/epoxy syntactic foams

The results of experimental and theoretical investigation of glass/epoxy syntactic foams at a long-term (10 years) exposure in water are presented. Specimens for experimental investigation were made from EDT-10 epoxy filled with MSO-779 hollow glass spheres. Seven types of specimens with filler volume fraction varying from 0 to 0.6 were tested. The curves of long-term water absorption and swelling were determined. It was expected that the addition of hollow glass spheres must substantially reduce the sorptional capacity of material because of the reduction of the volume content of the matrix and, therefore, because of reduction of the part of the volume where the molecules of water can diffuse. However, the water absorption process in syntactic foams was found to continue during the total term of the experiments without a tendency to stop. After ten years the limiting equilibrium state was not achieved and the concentration of water in composite specimens became higher than the equilibrium concentration of water in unfilled EDT-10 epoxy. In long-term tests the swelling strain was found to be a nonlinear function of water content. The degree of nonlinearity increased when the volume content of the filler was increased. The calculational prediction of absorption and swelling curves of syntactic foams with different volume contents of the filler was done using the experimentally determined characteristics of absorption of the matrix. The water transport process in the matrix was considered to obey Fick's law. It was found that the initial parts of the experimental curves (during the first year of exposure) show a good enough agreement with calculated data for engineering applications. Subsequently, the discrepancy between the experimental results and calculated data increased and reached such large values that the predicted results became unacceptable. The possible reasons of such discrepancy (breaking of adhesion bonds between the matrix and the filler with subsequent sorption of water at the glass sphere surface, and diffusional filling by water of the inner parts of the damaged glass spheres, etc.) are discussed.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995. University of Colima, Colima City, Colima, Mexico. Institute of Polymer Mechanics, Latvian Academy of Sciences, Riga, LV-1006, Latvia. Published in Mekhanika Kompozitnykh Materialov, No. 1, pp. 83–97, January–February, 1996.     

Macromechanical characteristics deduced from tests on glass/epoxy composites with optical methods

Experimental results are required to verify the simulation results obtained by the homogenisation procedure of a biaxial weftknitted fabric reinforced composite with the Binary Model [1]. Tensile, bending and shear tests were performed to investigate and validate the elastic macro‐mechanical behaviour of the composite material. Beside other methods an optical whole‐field measuring system was used to estimate the deformation in all tests. Additionally, natural frequencies and the appropriate mode shapes of plates were used to get the elements of the compliance matrix. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Micromechanical modelling and two-scale simulation of epoxy/glass composites with interphases and interfaces

Composite systems consisting of glass fibres and epoxy matrix with interphases and interfaces will be considered in the modelling approach. The interphase forms the transition zone between the epoxy matrix and the glass fibre. The interface is the layer between the glass fibre and the surrounding interphase. The macroscopic strength of the composite material is intrinsically related to the bond strength of the polymeric/solid interface and the micromechanical characteristics of the three phases (epoxy, glass and interphase). Homogenization is an appropriate methodology to link these two scales to predict the overall physical behaviour of the composite. The nonlinear behaviour of amorphous polymers, cohesive interface elements and the elastic behaviour of glass fibres as part of the considered composite material are presented, as well as a representative example to show the necessity of taking interface influences into account. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Choice of optimal structure of glass laminates with random reinforcement. I

The effect of structural parameters — length, diameter, and distribution of the reinforcing elements — on the mechanical characteristics of glass-reinforced plastics is investigated with reference to the case of glass laminates with randomly distributed, straight, uncut glass fibers in parallel planes. It is shown that the reduced strength of these laminates as compared with unidirectional material is associated with the redistribution of the load between the fibers and the resin and the relative reduction in the number of fibers in the cross section. A formula is proposed for estimating the strength of glass-reinforced plastics with a random distribution of the fibers in parallel planes.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fiber, Moscow Region. Moscow Bauman Higher Technical College. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1043–1050, November–December, 1968.