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The editorial comments on the multi-scale predictive modelling of the composite materials' behavior. Transition of composite materials from nano to micron to meter-size is examined keeping in view the accuracy of computation and fabrication methods. The article probes the physical behavior of complex material systems under stress in terms of size, time and environment.

Polymer composite materials are being increasingly used in primary load-bearing structures in several advanced industrial fields such as aerospace vessels, railway wagons and mega-scaled wind turbines where detection of subcritical damage initiation can significantly reduce safety issues and maintenance costs. It is therefore crucial to inspect these composite structures in order to assess their structural health and to ensure their integrity. Non-destructive testing techniques (NDT) are used for this purpose, making it possible to monitor mechanical damage of composite materials under in situ or ex situ service conditions. This paper reviews the capabilities of the most common NDT techniques used to inspect the integrity of composite materials. Each technique has a detection potential and cannot allow a full diagnosis of the mechanical damage state of the material. Thus, depending on the occurring damage mechanism and the conditions of use, one technique will be preferred over another, or several techniques should be combined to improve the diagnosis of the damage state of the structures. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are expected to be ideal reinforcements of composite materials used in aircraft and sports industries due to their high modulus and low density. In the present paper, severe plastic deformation by high pressure torsion (HPT) of powders at elevated temperature (473 K) was employed to achieve both powder consolidation and grain refinement of aluminum-matrix nanocomposites reinforced by 5 vol% CNTs. Before the HPT, the powders were ball milled using planetary ball mill in order to achieve molecular level mixing. Aluminum was treated by the same process for a reference. The HPT processed disk were composed of considerably equilibrium grain boundaries with high misorientation angles. The CNT-reinforced ultrafine grained microstructural features resulted in high strength and good ductility. [ABSTRACT FROM AUTHOR]

Acid treatment and triethylene-tetramine (TETA) modification of multi-walled carbon nanotubes (MWCNTs) purposing to attain better dispersibility and stronger interfacial bonding between MWCNTs and epoxy matrix have been carried out in this paper. The epoxy and MWCNTs/epoxy composites were produced by cast molding method. Stress–strain curves show that TETA-MWCNTs/epoxy hold the greatest toughness of all samples with 0.5 wt.% nanoparticles. The Young’s modulus of TETA-MWCNTs/epoxy has a significant increase about 38% compared to the neat epoxy, while the Young’s modulus of unmodified MWCNTs/epoxy or acid-modified MWCNTs/epoxy has a bit of decrease. Tensile and impact strength tests reflect that TETA-MWCNTs reinforced epoxy composites have an obvious improvement of tensile strength about 30% and an enhancement of impact strength over 34% compared to the pure epoxy composites with only 0.5 wt.% loading of TETA-MWCNTs. Scanning electron microscopy images of fractured surface of MWCNTs/epoxy indicate homogeneous dispersibility of TETA-MWCNTs and strong interfacial adhesion between the TETA-MWCNTs and the epoxy in the MWCNTs/epoxy composite. [ABSTRACT FROM AUTHOR]

In this paper, an accurate formula for calculating the thermal residual stress field in a particle-reinforced composite are presented. Numerical examples are given to show r-variations of the thermal residual stresses. The increase in fracture toughness of matrix predicted by the thermal residual stress field is compared well with the experimentally measured increase. [ABSTRACT FROM AUTHOR]

The very complex, multi-level hierarchical construction of textile composites and their structural components commonly manifests via significant property variation even at the macro-level. The concept of a “meso-volume” (introduced by this author in early 1990s) is consistently applied in this work to 3-D stress/strain and failure analyses of 3-D woven composites at several levels of structural hierarchy. The meso-volume is defined as homogeneous, anisotropic block of composite material with effective elastic properties determined through volumetrically averaged 3-D stress and strain fields computed at a lower (“finer”) level of structural hierarchy and application of generalized Hooke’s law to the averaged fields. The meso-volume can represent a relatively large, homogenized section of a composite structural component, a lamina in laminated composite structure, a homogenized assembly of several textile composite unit cells, a single homogenized unit cell, a resin-impregnated yarn, a single carbon fiber, even a carbon nanotube assembly. When composed together, distinct meso-volumes constitute a 3-D Mosaic model at the respective hierarchy level. A multi-scale methodology presented in this paper first illustrates 3-D stress/strain analysis of the Mosaic unidirectional composite, computation of its effective elastic properties and their further use in 3-D stress/strain analysis of the Mosaic model of 3-D woven composite Unit Cell. The obtained 3-D stress/strain fields are then volumetrically averaged within the Unit Cell, and its effective elastic properties are computed. The predicted effective elastic properties of 3-D woven composite are compared with experimental data and show very good agreement. Further, those effective elastic properties are used in 3-D simulations of three-point bending tests of 3-D woven composite; theoretical predictions for central deflection show excellent agreement with experimental data. Finally, a 3-D progressive failure analysis of generic 3-D Mosaic structure is developed using ultimate strain criterion and illustrated on the 3-D woven composite Unit Cell. The predicted strength values are compared to experimental results. The presented comparisons of theoretical and experimental results validate the adequacy and accuracy of the developed material models, mathematical algorithms, and computational tools. [ABSTRACT FROM AUTHOR]

The fracture process of composite laminates subjected to static or fatigue tensile loading involves sequential accumulation of intra- and interlaminar damage, in the form of transverse cracking, splitting and delamination, prior to catastrophic failure. Matrix cracking parallel to the fibres in the off-axis plies is the first damage mode observed. Since a damaged lamina within the laminate retains certain amount of its load-carrying capacity, it is important to predict accurately the stiffness properties of the laminate as a function of damage as well as progression of damage with the strain state. In this paper, theoretical modelling of matrix cracking in the off-axis plies of unbalanced symmetric composite laminates subjected to in-plane tensile loading is presented and discussed. A 2-D shear-lag analysis is used to determine ply stresses in a representative segment and the equivalent laminate concept is applied to derive expressions for Mode I, Mode II and the total strain energy release rate associated with off-axis ply cracking. Dependence of the degraded stiffness properties and strain energy release rates on the crack density and ply orientation angle is examined for glass/epoxy laminates. Suitability of a mixed mode fracture criterion to predict the cracking onset strain is also discussed. [ABSTRACT FROM AUTHOR]