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Introduction to Composite Materials
Published in Robert M. Jones, Mechanics of Composite Materials, 2018
Because of the inherently heterogeneous nature of composite materials, they are conveniently studied from two points of view: micromechanics and macromechanics: Micromechanics is the study of composite material behavior wherein the interaction of the constituent materials is examined on a microscopic scale to determine their effect on the properties of the composite material.Macromechanics is the study of composite material behavior wherein the material is presumed homogeneous and the effects of the constituent materials are detected only as averaged apparent macroscopic properties of the composite material.
Scaling in Tensile and Compressive Fracture of Concrete
Published in Alberto Carpinteri, Applications of Fracture Mechanics to Reinforced Concrete, 2018
In (numerical) micromechanical models the heterogeneity of the material is directly captured in the schematisation. The advantage of this is that the length scale due to the material itself is directly introduced. The crack-law can be very simple. A disadvantage of the method is that an incredible amount of computer capacity is needed for analysing a simple geometry containing only a few aggregates (see for example the Numerical Concrete developed by Roelfstra et al. [6]). The micromechanics models have a wide application. First of all they may be used for obtaining a better understanding of fracture processes. The entanglement between boundary condition influences and specimen size as touched upon in the first part of this chapter might be resolved with the micromechanics models. Based on this, assumptions made in higher order continua may be justified. For example the determination of the characteristic length can be based on micromechanics, as is done already in the analysis of the regular array of microcracks [37], but should be extended to include other crack interactions and crack–aggregate interactions as well. Another use of the micromechanics may be the design of new materials, tailored for specific applications. This is common practice in the field of ceramics [40], [41].
Introduction
Published in Xi Frank Xu, Multiscale Theory of Composites and Random Media, 2018
Micromechanics and multiscale modeling began to emerge in science and engineering in the 1950s and 1990s, not by coincidence, around the times when microfibers and nanotubes were fabricated leading to the births of composites technology and nanotechnology, respectively. Micromechanics is focused on understanding of the micro–macro relationship between macroscopic behavior and microscopic information of a composite. By extending the micro–macro bridging concept of micromechanics into a new territory occupied by multiple scales, multiscale modeling of materials has introduced many new tools, and certainly many challenges as well, to deal with phenomena newly observed or not well understood. A most critical challenge confronting multiscale modeling is to fit so-called scale-coupling phenomena into the current theoretical framework of mechanics, or alternatively, as exhorted by this book, to develop new theory of scale-coupling mechanics.
Micro metal powder hot embossing: influence of binder on austenitic stainless steel microparts replicability
Published in Powder Metallurgy, 2022
E. W. Sequeiros, M. T. Vieira, M. F. Vieira
Microfabrication technologies are emerging due to the increasing demand in microengineering applications, such as micromoulds, micromechanical structures, sensors, and micromedical devices. They are considered promising technologies for today and the near future, but they still have challenges to overcome [1,2]. Micro hot embossing and micro-polymer injection moulding are replicative technologies well established for the mass production of low-cost polymer microparts or devices [1,2]. However, there are specifications that polymers do not accomplish, such as mechanical properties and thermal stability. Micro metal injection moulding (microMIM) has been developed to overcome polymer limitations [3,4]. Metal micro powder hot embossing is a recent sustainable process based on MIM that can provide complex geometries for small metallic parts at low cost and without waste [5,6]. In general, hot embossing is a replicative process that provides microparts and in which shaping occurs by applying heat and pressure for predefined times [1]. In the last decade, the optimisation of this new replicative process for metallic powder remains an objective of the research. Several scientific studies address the control of the main factors determining the quality of hot embossing parts, such as shaping process parameters (temperature, pressure, and time), rheological properties, and die surface finishing [7–14]. Hot embossing and micro hot embossing techniques can be carried out in the laboratory using a relatively unsophisticated hot press [15].
The development of a global mix design and analysis approach for alkali activated soil reinforcement grouts
Published in European Journal of Environmental and Civil Engineering, 2019
This paper presents some results of an approach to formulation and characterisation of alkali activated grout for soil reinforcement. The aspects that were examined range from the physicochemical properties of the reaction products, to the micromechanical and rheological behaviour, as well as the development of the structure and an assessment of their durability performance in acid environments. The main results are:First, the use of metakaolin-fly ash binary combinations has overcome the rheological limitations imposed by the absence of effective industrial admixtures.The effect of calcium levels on the products formed and the reaction process was emphasised through the comparison of slag and metakaolin.An analysis methodology based on micromechanics was presented, which ultimately made it possible to predict the macroscopic behaviour of the material.Finally, geopolymer grouts have been shown to be particularly suitable for use in acidic media that are too aggressive for traditional binders. This result confirms the usefulness of such materials for soil reinforcement, starting with acid-exposed soils.
Impact properties of thermoplastic composites
Published in Textile Progress, 2018
Ganesh Jogur, Ashraf Nawaz Khan, Apurba Das, Puneet Mahajan, R. Alagirusamy
Different combinations of failure mechanisms exist in composites, and they require different failure criteria, which further depend upon matrix and fibre failures. Totry et al. [238] studied the composite failure under transverse compression and out-of-plane shear stress; the authors considered three failure criteria namely those of Hashin, Puck, and LaRC, and also reported a new failure criterion with help of the simulation having interface de-cohesion. The author suggested using interface de-cohesion in the simulation either in case of matrix dominated failure or fibre failure in compression mode. In another study, Totry et al. [239] discussed the prediction of failure location of the composite under transverse compression and longitudinal shear using computational micromechanics. Computational micromechanics is a tool for the prediction of composite materials’ macroscopic behaviour using representative volume element (RVE) in the microstructure via numerical simulation.