Bending strength of oriented glass-reinforced plastics

The authors consider the effect of the low shear strength and shear stiffness of oriented glass-reinforced plastics (GRP) on the stress distribution and type of failure in bending. On the basis of relations obtained in [1] it is shown that the effect of shears on the magnitude and law of distribution of the normal and shear stresses is important only for very short beams made of materials with a low shear stiffness. An experimental study of the nature of failure in bending has revealed that the chief cause of extension of the region of shear failure of oriented GRP is the low shear strength of the material, and has made it possible to establish the limits of this region for three typical materials. Anisotropy of the elastic properties has little effect on the type of failure in bending.Mekhanika Polimerov, Vol. 2, No. 4, pp. 535–542, 1966     

Investigation,Modelling and Analysis of stiffened GFRP-Samples

Glasfibre structures feature high potentials for optimization and substitution of conventional materials like steel and aluminum and their alloys. The paper deals with the insertion of glasfibre trusses into thin glasfibre structures to reinforce them. The effective material properties of the glasfibre structures were estimated by experiments and simulations. Furthermore the Young's modulus of the trusses was obtained by bending tests and tension tests. A comparison between bending experiments and bending simulations is given. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measuring the tensile and bending properties of nanohoneycomb structures

The mechanical properties, including Young’s modulus, the effective bending modulus, and the nominal fracture strength, of nanohoneycomb structures were measured by using an atomic force microscope (AFM) and a nano-universal testing machine (UTM). Anodic alumina films were taken as the nanohoneycomb structures. Bending tests were carried out on cantilever beams by pressing AFM tips, and the results were compared with three-point bending tests and tensile tests conducted by using the nano-UTM. A new and less damaging method for gripping the specimens was elaborated for the tensile tests. The results obtained can serve as design guidelines in applications of nanohoneycomb structures. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 247–264, March–April, 2006.     

Experimental estimation of the transverse tensile strength of carbon-reinforced plastics

The transverse tensile strength of carbon-reinforced plastics is estimated on the basis of the results of bending tests on open rings and segments. It is shown that structural discontinuities due to technological factors sharply reduce the transverse tensile strength of carbon-reinforced plastics. The radial stresses have an important influence on the strength of segments tested in three-point bending.     

Effect of sign-variable thermocycling on the mechanical properties of carbon-fiber plastics with various layups

Conclusion An economic method for the ST of carbon-fiber-reinforced plastics is proposed in this study. It is established as a result of investigations of the mechanical properties of carbon-fiber-reinforced plastics with different layups, which are subjected to ST in the range to 100 cycles, that in the majority of cases, the number and duration of thermal cycles has no effect on the stiffness and strength in tension, compression, bending, and shear. The effect of number of thermal cycles was manifested only on the stiffness in tension and bending and also on the tensile, compressive, and bending strengths of the material with the obliquely reinforced structure loaded in the direction of the diagonal. It is permissible to use the dynamic method to assess variations in the stiffness of a material subjected to ST.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 1, pp. 66–76, January–February, 1993.     

Investigation of the relations between the various mechanical properties and the biochemical composition of human bone tissue

Nondestructive and destructive methods have been used to establish a series of elastic and strength characteristics of the compact bone tissue in six zones of the cross section of the diaphysis of the human tibia. The quantity of five characteristic biochemical substances present in each zone has been determined. The experiments show that, from the standpoint of continuum mechanics, the compact bone tissue is an orthotropic material and that the bone is nonhomogeneous with respect to biochemical composition. The rank correlation coefficients between the mechanical characteristics and the biochemical concentrations are subjected to a detailed analysis. The important effect of the common glycoproteins on the elastic and strength properties of bone tissue in tension is established.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 138–145, January–February, 1973.     

Physicomechanical properties of composites from recycled polyethylene and linen yarn production wastes

The possibilities of utilizing wastes of linen thread production (chaffs, spinning and roving losses) in recycled polyolefin composites have been investigated. The wastes were mixed with recycled polyethylenes (produced from domestic and industrial film production wastes). The physicomechanical properties (tensile strength, bending and tensile moduli, and water resistance) and the fluidity (melt flow-behavior index) for systems with a different filler content are estimated. Almost all the composite materials obtained have satisfactory fluidity (melt flow-behavior index is not lower than 0.07–0.15 dg/min). For all types of the composites, a slight increase in tensile strength and a considerable increase (3–7 times) in bending and tensile moduli were observed. The water resistance of the composites decreased with an increase in the filler content. The modification of filled systems with diisocyanates (diphenylmethane diisocyanate) improved the useful properties and water resistance of all the composites investigated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 2, pp. 199–210, March–April, 1999.     

Strength of fresh bone and bone preserved by freezing

The bending strength of 85 plates obtained from the tibias of human cadavers has been determined and compared with the strength of plates of bone tissue from the same bone stored at temperatures from ?25 to ?30°C for 3 months (44 cases), 6.5 months (32 cases), and 9.5 months (32 cases). It is found that the strength of the deep-frozen bone decreases with time.     

Experimental Evaluation of the Effect of the Structure of Composite Rings on Their Properties in the Radial Direction

Based on the results of bending tests on cut glass-fiber-reinforced plastic rings with a longitudinal-circumferential reinforcement, their radial peel strength is evaluated. The effect of the fiber layout on the properties of the rings in the radial direction is investigated. It is shown that their radial tensile strength only slightly depends on the fiber layout but is basically determined by the properties of the polymer interlayer between the fibers. In radial tension, the presence of fibers in the polymer layer leads to a strain concentration, which results in a premature failure of the polymer phase of the composite. The strain-concentration factor cannot be used for an accurate prediction of the breaking stresses or strains of the composite, because of different failure modes of the pure resin and the composite.     

The ultimate state of polymeric materials and laminated and fibrous composites under asymmetric high-cycle loading

The prediction of the high-cycle fatigue strength of polymeric and composite materials in asymmetric loading is considered. The problem is solved on the basis of a nonlinear model of ultimate state allowing us to describe all typical forms of the diagrams of ultimate stresses. The material constants of the model are determined from the results of fatigue tests in symmetric reversed cycling, in a single fatigue test with the minimum stress equal to zero, and in a short-term strength test. The fatigue strength characteristics of some polymers, glass-fiber laminates, glass-fiber-reinforced plastics, organic-fiber-reinforced plastics, and wood laminates in asymmetric tension-compression, bending, and torsion have been calculated and approved experimentally. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 1, pp. 87–102, January–February, 2008.     

Physicomechanical properties of composites from recycled polyethylene and linen yarn production wastes

The possibilities of utilizing wastes of linen thread production (chaffs, spinning and roving losses) in recycled polyolefin composites have been investigated. The wastes were mixed with recycled polyethylenes (produced from domestic and industrial film production wastes). The physicomechanical properties (tensile strength, bending and tensile moduli, and water resistance) and the fluidity (melt flow-behavior index) for systems with a different filler content are estimated. Almost all the composite materials obtained have satisfactory fluidity (melt flow-behavior index is not lower than 0.07–0.15 dg/min). For all types of the composites, a slight increase in tensile strength and a considerable increase (3–7 times) in bending and tensile moduli were observed. The water resistance of the composites decreased with an increase in the filler content. The modification of filled systems with diisocyanates (diphenylmethane diisocyanate) improved the useful properties and water resistance of all the composites investigated.     

Deformation and failure of angle-plied organic fiber-reinforced plastics in the 3D stress state

Tubular specimens of organic fiber-reinforced plastic (OFRP) are tested in tension under a high hydrostatic pressure of up to 300 MPa. The specimens are made by winding at an angle of ±60° to the generatrix. The experimental equipment and technique are described. The tests show the insignificant effect of hydrostatic pressure on the elastic properties and the failure mode of the OFRP. The hydrostatic pressure considerably affects the strength properties of the OFRP. The material strength increases almost twofold under a pressure of 300 MPa. The failure strains of the material increase significantly as well.N. E. Bauman Moscow Higher Technical School, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 5, pp. 592–602, September–October, 1997.     

Dynamic response of fiber-reinforced composite plates

The dynamic stability of orthotropic thick plates subjected to a periodic uniaxial stress and a bending stress is investigated. Both the rotary inertia and the transverse stress are considered in the investigation. The governing equations of motion of Mathieu type are established by applying the Galerkin method with reduced eigenfunction transforms. Based on Bolotin’s method, the dynamic instability regions of graphite- and glass-fiber-reinforced plates are evaluated by solving eigenvalue problems. A dynamic instability index is defined and used as an instability measure to study the influence of various parameters. The effects of material properties and load parameters on the instability region and on the index of dynamic instability of orthotropic plates are discussed.     

The Effect of an Active Diluent on the Properties of Epoxy Resin and Unidirectional Carbon-Fiber-Reinforced Plastics

The influence of an active diluent on the properties of an epoxy matrix and carbon-fiber-reinforced plastics (CFRP) is investigated. The physicomechanical properties of an ED-20 epoxy resin modified with diglycidyl ether of diethylene glycol (DEG-1), the adhesion strength at the epoxy matrix–steel wire interface, and the mechanical properties of unidirectional CFRP are determined. The concentration of DEG-1 was varied from 0 to 50 wt.%. The properties of the matrix, the interface, and the composites are compared. It is stated that the matrix strength affects the strength of unidirectional CFRP in bending and not their strength in tension, compression, and shear. The latter fact seems somewhat unexpected. The interlaminar fracture toughness of the composites investigated correlates with the ultimate elongation of the binder. A comparison between the concentration dependences of adhesion strength and the strength of CFRP shows that the matrices utilized provide such a high interfacial strength that the strength of CFRP no longer depends on the adhesion of its constituents.     

Macroscopic damage modeling for silicon nitride

Modeling the damage of brittle materials is of great importance considering a variety of structural components. Prominent examples are high strength engineering ceramics. The present work is concerned with silicon nitride, a material with increasing relevance in industrial applications. In the sense of a hierarchical model structure, effective properties of micromechanical simulations were applied to macroscopic, phenomenological damage models for monotonous and cyclic loading. In the following, both models are introduced and the application of the cyclic damage model to a four point bending test is discussed. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy in the destruction of compact bone material

Conclusions 1. The nature of the destruction of compact bone material upon short-term static compressive and tensile stresses, as well as upon impact bending, is a function of the anistropy of the structure on the osteon level.2. The compact bone material of femoral bones of the age range studied is destroyed by shear for the types of stresses indicated.3. The nature of the destruction of samples of compact bone material for the stresses studied may be generalized for tubular bones.Kurgan Scientific-Research Institute of Experimental and Clinical Orthopedics and Traumatology. Translated from Mekhanika Polimerov, No. 2, pp. 319–324, March–April, 1978.     

Effect of building structure on the distribution of random bending strength of multilaminate reinforced plastics

A probabilistic structural model has been constructed for predicting the bending strength distribution in multilaminate reinforced plastics. The number and random strength/elastic properties of the layers or repeating structural elements are parameters of the structure. The random properties of the repeating structural elements are characterized by the scheme and geometry of the unidirectional layers. Two failure conditions have been analyzed: multistep failure caused by successive failure of separate layers and failure caused by the failure of the weakest component. The effect of the number of layers and the instability of the strength and elastic properties on the basic statistical properties of the bending strength was analyzed numerically for typical structures and for both failure conditions. The quantitative significance of the size effect determined by the thickness of the plastic was investigated. The main theoretical results were checked experimentally for unidirectional reinforced carbon plastic under uniaxial bending. The experimental distribution agrees well with the predicted distribution.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 3, pp. 336–344, May–June, 1993.     

Constitutive modeling of fiber-reinforced aerogels

Aerogels are open-cell highly porous solids having exclusive properties such as lowest bulk density, lowest thermal conductivity and lowest acoustic velocity. These properties make them useful over a large spectrum of applications. However, their brittle and hydrophilic natures result in a road block which is overcome by polymer or fiber reinforcement. In this study, we are focussing on fiber-reinforced aerogels which retain the exclusive properties of aerogels mentioned above while giving them a good load bearing strength at the same time. These fiber-reinforced aerogels show many complex phenomena under loading such as, a strong nonlinearity, cyclic stress softening, and permanent set. However, there have been very few studies on fiber-reinforced aerogels oriented towards their mechanical characterization. To the best of our knowledge, there also is no micromechanical model that can capture the constitutive response of these fiber-reinforced aerogels. In this contribution, we propose a micro-mechanically motivated constitutive model of fiber reinforced aerogels. The prime source of elasticity and damage in these aerogels is the effect of bending and breakage of fibers in the material network. Accordingly, we consider non-linear bending of fibers supported by an elastic foundation of particles. Based on this concept, the strain energy function is analytically derived for a single fiber in a particular direction. The strain energy of the whole network is then obtained by integration over an unit sphere. The model shows good agreement with experimental data. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of temperature and moisture on the mechanical properties of polyester resin in tension

The effect of environment on the physical and mechanical properties of composite materials in some cases is determined by the environmental sensitivity of the binder. The results of experimental investigation of the deformability and strength of polyester resin, widely used as a binder in composites, upon the action of stationary and quasi-stationary loads, temperatures, and moisture are presented. The ranges of acceptable values of these services factors are determined. The elastic modulus and tensile strength of the material are obtained from quasi-static tests. The viscoelastic behavior of the resin is investigated in creep tests. From the results of a short-term experiment with stepwise loading up to failure, it is found that the creep of specimens with a moisture content of 0.14% can be described by a linear viscoelastic model for stresses up to 20 MPa (two thirds of the strength). The action of single loading impulses is summarized according to the Boltzmann superposition principle. The temperature and absorbed moisture are considered as factors accelerating the relaxation processes in the material. The creep activation under the action of these factors is described using the methods of time-temperature and time-moisture equivalence. The results of short-term creep tests allow us to determine the relaxation characteristics of the material in stationary conditions. The long-term creep under close-to-service conditions is predicted using these data and quite good agreement with the control test is obtained. The sensitivity of the material characteristics (strength, elastic modulus, and creep strain) to the action of temperature and moisture is estimated. The creep strain is most sensitive to the action of environmental factors. For a fully saturated material (moisture content 1.64 wt.%), after one hour creep, this strain four times exceeds that of a dry one. The same growth in deformability is caused by an 18°C increase in temperature. A quantitative comparison of the characteristics of polyester and epoxy resins allows us to choose the binder for composites and to estimate the expected environmental effect. Presented at the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 395–406, May–June, 2000.     

Effect of Water Absoption,Elevated Temperatures and Fatigue on the Mechanical Properties of Carbon-Fiber-Reinforced Epoxy Composites for Flexible Risers

The influence of water absorption, under different temperatures and thermal aging in an oven, on the elastic and strength characteristics of carbon-fiber-reinforced epoxy composites is investigated by comparative tests in three-point bending. The tension-tension fatigue behavior of the composites is also studied.