Mechanics of Composite Materials最新文献

Hybrid composite materials reinforced with nanoscale additives provide better mechanical properties than traditional composites. Carbon-fiber-reinforced polyether ether ketone with various layups modified by 0.05-0.36 wt% of single-wall carbon nanotubes was experimentally studied. The influence of the nanotubes on the mechanical properties of the composites, found in tensile and bending tests, and on their electrical conductivity was studied and discussed. Adding 0.15 wt% of SWCNTs between layers of prepregs led to an increase in the tensile strength by 9.9% and flexural strength by 5.5%. The electrical conductivity of the unidirectional composite has not been changed significantly after the incorporation of SWCNTs, while for orthotropic layup it increases by 65%.

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model for shear flow of thixotropic viscoelastic-plastic media, which takes into account the mutual influence of the deformation process and structure evolution, is continued. A set of two nonlinear differential equations describing the processes of shear at a constant rate and stress relaxation is obtained. Equation set describing creep is derived; a general solution of the Cauchy problem for the set is constructed in an explicit form (the equations of the families of creep, and structuredness curves are derived). For arbitrary six material parameters and (increasing) material function that govern the model, basic properties of the families stress-strain curves at constant strain rates, stress relaxation curves and creep curves generated by the model, and the features of structuredness evolution under these types of loading are analytically studied. The dependences of these curves on time, shear rate, stress level, initial strain, and initial structuredness of the material, as well as on the material parameters and function of the model, are studied. Several indicators of the applicability of the model are found which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (unusual properties) are generated by a change in structuredness in comparison with typical stress-strain curves, relaxation curves, and creep curves of structurally stable materials. In particular, it is proved that creep curves always increase in time and have oblique asymptote, and structuredness under constant stress is always monotonous (unlike other loading modes), but can decrease or increase depending on the relation between the stress level and initial structuredness. The same condition controls creep curves to be convex up or down: at a certain (calculated) critical load creep curves change from convexity up (under smaller loads) to convexity down, and the structuredness becomes ascending instead of descending. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves, strain rate and strain hardening, flow under constant stress and so on.

This study aims to analyze the in-plane free vibrations of arches comprising the laterally symmetric functionally graded materials. Emphasis is placed on the circular arch whose material properties vary laterally symmetrically about the centroidal axis by a power-law function. The differential equations governing the mode shape of the arch were derived under the boundary conditions and were numerically solved to calculate the natural frequencies using the Runge–Kutta and Regula–Falsi methods. Calculation results of this study for natural frequencies compare well with those of the finite element method. The effects of various arch parameters on natural frequencies are highlighted and discussed in detail.

It is known that the initial fiber waviness affects the stiffness and strength of the polymer composite material. The influence of degree of waviness on stiffness characteristics under uniaxial tension and compression of a polymer composite material was investigated by using numerical modeling. A computational approach based on a special periodicity cell with different fiber waviness was developed. The hypothesis regarding the impact of manufacturing stresses, appearing during a curing process on waviness growth, was tested. The results obtained explain the mechanism that causes difference in the stiffness observed in fiber composites in the longitudinal direction under uniaxial tension and compression.

MECH-Gcomp was developed as web-based free software to aid in learning and to help researchers and industry professionals in failure analysis of composite materials. The software is already well-established for the study of micromechanics and has extended to other fields. This work focuses on one of its newest modules, related to the failure analysis of composite laminae, for which thirteen different failure criteria were implemented, along with an important tool for the construction of failure envelopes. The programming and characteristics of this module are presented and discussed. In addition, jute/polyester composites were manufactured and tested under different stress states to verify the software predictions. The root-mean-square error ranged from 0.096 to a maximum of 0.545, and most of the analyzed criteria yielded reasonable agreement compared to the experimental data. A significant variation in predictions among the criteria could be clearly observed, especially based on the produced failure envelopes for the different stress states.

Carbon fiber reinforced-polylactic acid (CF-PLA) composites nowadays are widely researched alternative structural materials for their potential application in prosthetic and orthotic implants. The present work firstly consolidates the findings on the application of 3D printing in biomedical and allied fields. Fatigue life and impact strength of 3D printed CF-PLA test specimens were determined. The test specimens were fabricated through the fused deposition modeling (FDM) approach at two printing temperatures. The pronounced effect of printing temperature is characterized by the significant change in fatigue life and impact strength of the FDM specimen. The fatigue life at the printing temperature of 240°C was 2.7 times greater than that at 225°C, whereas the impact strength was greater by 5.93%. The microscopy findings revealed increased diffusion and a reduced number of ridges and pores at higher printing temperature testifying that printing temperature prominently controls the durability and impact response of FDM printed parts.

This study focuses on the effect of copper nanoparticles and graphene oxide nanosheets on the tensile properties and impact strength of epoxy-based hybrid nanocomposites. A mechanical mixer and an ultrasonicator were used to mix the reinforcements with the epoxy resin. Field Emission Scanning Electron Microscope (FE-SEM) was used to examine the fracture surface morphology, and tensile and impact tests were conducted to assess the mechanical properties of the nanocomposites. These properties were optimized by a genetic algorithm. The results showed that adding 0.75 wt% copper nanoparticles and 1 wt.% graphene oxide to the epoxy increased its tensile strength by 45.7 and 37.14%, respectively, compared with those of pure epoxy, and adding 0.5 wt% graphene oxide and 0.75 wt% copper nanoparticle led to a 61.76 and 32.35% increase in its fracture strength. The tensile test results indicated that the tensile strength of specimens reinforced with 0.125 wt% graphene oxide and 0.125 wt% copper nanoparticles increased by 47.51% compared with those of pure epoxy and adding 0.375 wt% graphene oxide and 0.375 wt% copper nanoparticles increased the fracture energy by 91.18%.

Bio-based composites with passive control layers were investigated by means of a comprehensive set of experiments. The structure, composed of an exterior layer of PLA/Flax and an inserted rubber layer, were manufactured using 3D printing technology. Tensile tests on PLA/Flax and rubber specimens revealed that it exhibited higher stiffness, whereas rubber demonstrated superior elongation. Additionally, three-point bending tests were conducted on 3D-printed composites with varying viscoelastic layer thicknesses (VL) to assess their bending performance. However, the composite with a single 1-mm thick viscoelastic layer (V₁t₁) showed optimal deflection and stiffness compared to counterparts with different viscoelastic layers. Furthermore, resonance vibration experiments were performed to investigate dynamic parameters such as frequencies and modal loss factors. Based on the experiments, it was determined that V₁t₁ was the composite that offered the optimal compromise between mechanical and vibration behavior due to its excellent damping characteristics.

The aim of the present study is to use beech wood flour (WF) and expanded ethylene vinyl acetate (EVA) copolymer industrial waste to develop a sustainable composite and its production method for further engineering use. Polyamide (PA) powder waste obtained after multiple selective laser sintering (SLS) thermal cycles was used to increase the strength and adhesion between the waste composite components. The morphological, mechanical, and thermal properties of the EVA/WF composites were characterised along with their interfacial wetting and water absorption properties. Optical and electron microscopy investigations revealed that the composites prepared have homogeneous dispersion and good interfacial adhesion between EVA and wood. The addition of SLS waste PA powder increases the strength and stiffness of the composite developed. The composite with 40 wt% WF exhibited the best water absorption, mechanical properties, and processability among the various compositions. The sustainable composite proposed can replace commercially available materials, which helps to save resources and reduce waste.

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model for shear flow of thixotropic viscoelastic-plastic media is continued. For arbitrary six material parameters and an (increasing) material function that control the model, the basic properties of the families of stress-strain curves at constant strain rates and relaxation curves generated by the model, and the features of the evolution of the structuredness under these types of loading are analytically studied. The dependences of these curves on time, shear rate, initial strain and initial structuredness of the material, as well as on the material parameters and function of the model, are studied. Several indicators of the applicability of the model are found which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (unusual properties) are generated by a change in structuredness in comparison with typical stress-strain curves and relaxation curves of structurally stable materials. In particular, it has been proved that stress-strain curves can be both increasing functions and can have decreasing sections resembling a “yield tooth” or damped oscillations, that all stress-strain curves (SSCs) possess horizontal asymptotes (steady flow stress), monotonically dependent on shear rate, and flow stress increases with shear rate growth, that the instantaneous shear modulus, on the contrary, depends on the initial structuredness, but does not depend on shear rate. Under certain restrictions on the material parameters, the model is also capable of providing a bilinear form of stress-strain curves, which is typical for an ideal elastoplastic model, but with strain rate sensitivity. It has been established that the family of stress-strain curves does not have to be increasing either in initial structuredness or in shear rate: in a certain range of shear rates, in which the equilibrium position is a “mature” focus and pronounced oscillations of stress-strain curves are observed, it is possible to intertwine stress-strain curves with different shear rates. It is proved that for any material parameters and functions, all stress relaxation curves decrease and have a common zero asymptote as time tends to infinity. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves, strain rate and strain hardening, flow under constant stress and so on.