Polymer composites stress

Nassehi, V., Kinsella, M. and Mascia, 1.., 1993b. Finite element modelling of the stress distribution in polymer composites with coated fibre interlayers. J. Compos. Mater. 27, 195-214. 

The mechanical piopeities of stmctuial foams and thek variation with polymer composition and density has been reviewed (103). The variation of stmctural foam mechanical properties with density as a function of polymer properties is extracted from stress—strain curves and, owkig to possible anisotropy of the foam, must be considered apparent data. These relations can provide valuable guidance toward arriving at an optimum stmctural foam, however. 

Therefore in many cases, where the behavior of polymer compositions under real technological conditions is of practical interest, i.e. in the region of high deformation rates, the yield stress and the region near it may be neglected and only upper branches... 

We conclude that the preparation of the samples of the polymer composites with the corresponding electrical properties in the form, say, of the plates, bars, hollow cylinders, etc., that are usually used for the purpose of research in the laboratories, and of real articles should be considered as two interrelated problems. This is important and should be stressed, as the values of the conductivity and other parameters obtained for the simple forms might prove different for the forms that may be used as constructional elements. Therefore, these circumstances should be taken into account at the design stage of a conducting composite as well as the optimum technological techniques of molding of practically important articles. 

Adhesives and sealers can be an important part of a total corrosion protection system. Structural bonding procedures and adhesives for aluminum, polymer composites, and titanium are well established in the aerospace industry. Structural bonding of steel is gaining increasing prominence in the appliance and automotive industries. The durability of adhesive bonds has been discussed by a number of authors (see, e.g., 85). The effects of aggressive environments on adhesive bonds are of particular concern. Minford ( ) has presented a comparative evaluation of aluminum joints in salt water exposure Smith ( ) has discussed steel-epoxy bond endurance under hydrothermal stress Drain et al. (8 ) and Dodiuk et al. (8 ) have presented results on the effects of water on performance of various adhesive/substrate combinations. In this volume, the durability of adhesive bonds in the presence of water and in corrosive environments is discussed by Matienzo et al., Gosselin, and Holubka et al. The effects of aggressive environments on adhesively bonded steel structures have a number of features in common with their effects on coated steel, but the mechanical requirements placed on adhesive bonds add an additional level of complication. 

Nairn, J.A. (1985). Thermoelastic analysis of residual stresses in unidirectional high-performance composites. Polym. Composites 6, 123-130. 

Piggott, M.G. and Woo, M.S. (1986). Fiber composites with internal stresses under control. Polym. Composites 1, 182 185. 

The high strength of polymer composites is dependent on a transfer of external stress from the resin matrix to the fiber or filler. The efficiency of this transfer is dependent on the strength of the interfacial bond between the... 

Elmughrabi, A. E., Robinson, M., and Gibson, A. G. Effect of stress on the fire reaction properties of polymer composite laminates, Polym. Degrad. Stabil. 2008, 93, 1877-1883. 

The gap between the predictions and experimental results arises from imperfect dispersion of carbon nanotubes and poor load transfer from the matrix to the nanotubes. Even modest nanotube agglomeration impacts the diameter and length distributions of the nanofillers and overall is likely to decrease the aspect ratio. In addition, nanotube agglomeration reduces the modulus of the nanofillers relative to that of isolated nanotubes because there are only weak dispersive forces between the nanotubes. Schadler et al. (71) and Ajayan et al. (72) concluded from Raman spectra that slippage occurs between the shells of MWNTs and within SWNT ropes and may limit stress transfer in nanotube/polymer composites. Thus, good dispersion of CNTs and strong interfacial interactions between CNTs and PU chains contribute to the dramatic improvement of the mechanical properties of the... 

The main experimental methodology used is to directly characterize the tensile properties of CNTs/polymer composites by conventional pull tests (e.g. with Instron tensile testers). Similarly, dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were also applied to investigate the tensile strength and tensile modulus. With these tensile tests, the ultimate tensile strength, tensile modulus and elongation to break of composites can be determined from the tensile strain-stress curve. 

By analyzing the compositional dependent relaxation time, the stress-strain relationships of polymer composites are determined as a function of the filler concentration and strain rate. As the volume fraction of filler increases, both the effective elastic modulus and yield stress increases. However, the system becomes more brittle at the same time. 

The effect of speed on wear rate is probably due at least partly to the fact that polymers commonly exhibit visco-elasticity. As a result, increased contact speeds can lead to higher contact stresses. Higher speed also causes higher frictional heating, which will usually result in softening and increased wear. However, the use of polymer composites is best restricted to speeds below one or two metres/second because the combination of frictional heating and poor thermal conductivity leads to overheating and breakdown. 

Galiotis, C., Laser Raman spectroscopy, a new stress/strain measurement technique for the remote and on-line non-destructive inspection of fiber reinforce polymer composites. Mater. TechnoL, 8, 203, 1993. 

Brunner A.J., Blaclman, B.R.K., Williams, J.G. Deducing Bridging Stresses and Damage from Gic Test on Fibre Composites (at press). Proceedings 3 " ESIS TC4 Conference on Fracture of Polymers, Composites and Adhesives, Elsevier. 

Faflure in multiphase polymers and polymer composites (non-fibrous) is reviewed by Professor Bucknall. Several examples are presented in which the effect of adding a dispersed second phase to a polymer can be either beneficial or deleterious to stress, strain, or work to break. It is shown that two basic modes of local plastic deformation may be operative, namely crazing and shear band formation. 

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