很多同学找**英国Assignment辅导**会首先考虑价格问题。诚然，价格还是要比一比的，但是价格后面的问题你们考虑多少呢，又了解多少呢？

就像去餐厅吃饭，一顿看起来令人大快朵颐的好餮大餐没有一个折扣的广告牌，或许知道的人少之又少。那么，看到广告牌入内以后，即便钱交了，东西入口了，厨房的情况你们又知道多少呢？

地沟油，以次充好，脏乱差，这些不仅仅是餐饮业的普遍问题，**英国辅导**市场也是比比皆是，不言而喻的潜规则在光鲜的营销策略下令人羞愧。

下面的文章使我们的一个范本，抽取一段大家可以看看

**A Multiscale Prediction of Elasticity of Cement Paste at Early Age Based on ****Percolation**

**Abstract****：***As an evolving component of concrete, the cement paste plays an important role on the mechanical properties. It is well known that the mechanical characteristics of cement paste, which is random, complex, multiscale composite, follows a rapid change at early age. This paper focuses on the evolution in the elasticity of the cement paste during the hydration, e.g. Young’s modulus and Poisson’s ration, which proposed by the homogenization method combined the percolation algorithm with individual phase intrinsic elasticity. A paste development model of the cement, named CEMHYD3D, is used to capture an accurate microstructural model. The model results are in good agreement with the experimental data and other numerical results, which are available in the open literature. *

*Keywords:**Multiscale; Microstructure; Early age; Cement paste; Percolation; Elasticity*

**1. INTRODUCTION**

Young’s modulus, in which the compressive and tensile strengthof hardening and hardened cement-based materials are the vital parameters used in the structural design and analysis of concrete structure. Especially, it is known that the rate of development of Yong’s modulus is considerably faster than that of compressive and tensile strength, which is reaching a significant fraction of its final value after a few days. The stresses that are generated in structures are also closely related to the rapid development of the Young’s modulus, which makes it as an essential parameter to be studied in order to better understand the behavior of the cement-based materials. It is very helpful to know the microstructure evolution of the hydrating material to understand the development of the material properties, as it is believed that, at the microstructure level , the microstructure evolution governs the material mechanical properties[Maekawa *et al*., 2009; Breugel, 1991; Garboczi *et al*., 1999; Venkiteela *et al*., 2010].

Bernard proposed an analytical homogenization approach to study the aging elasticity of cement-based materials[Bernard*et al*., 2003]. The authors considered the microstructure of the concrete at four different levels, and chose a suitable homogenization approach, e.g. Mori-Tanaka scheme(MT) and/or self-consistent scheme(SCS) at each level, which bridge the gap between the physical and chemistry during the process of hydration and the mechanics, however, the proposed model could only give realistic values for high water to cement(w/c) ratios and fail to predict the low w/c ratios for obtaining non-zero values below percolation threshold. Sanahuja modified the aspect ratio of the hydration product to predict the elasticity of cement-based materials at early age[Sanahuja*et al.*, 2007]. Still, the authors did not successfully predict the evolution of Young’s modulus at the early age, e.g. the hydration degree is smaller than 0.3. Smilauer reconstructed a digital image of the hydrating cement paste given by the CEMHYD3D hydration model[Smilauer*et al.*, 2007;Bentz, 2000]. The authors showed that numerical homogenization yielded more accurate results, however, the presented method is only appropriate for a w/c ratio higher than 0.35 and predict a stiffer response of Young’s modulus at early age, besides, the FEM method was a too heavy computational method for the computation of development of properties of cement paste at early age. Sun proposed a approach that considered hydrate products coming into contact with the advancement of hydration and the contact area among the particles, which was the essential factor that dominates the mechanical properties of the system[Sun*et al.*, 2005]. Sanahuja improved the prediction accuracy of early age elasticity evolution by modifying the aspect ratio of C-S-H and in terms of percolation threshold, and clearly illustrated a change in the response of the homogenization method used by changing the morphology of the inclusion[Sanahuja*et al.*, 2007], which was generally considered sphere-shaped [Pichler*et al.*, 2009]. Still, they pointed out that the agreement was not good at very early age, e.g. hydration degree was smaller than 0.3. Therefore, it is problematic for the prediction of elasticity of cement paste at early age without considering the transition from a suspension to a solid structure.

The goal of this paper is to propose a model relating the intrinsic properties of its individual chemical phase in effective elastic properties of cement paste at the nano- and micro-level using upscaling methods, for the prediction of elasticity of cement paste, especially at very early age when cement-based material evolves from a close to plastic state to a solid state by applying solid phase percolation concept.

**2. Fundamentals of continuum micromechanics**

**2.1. Representative volume elements (RVE) and separation of scales principle**

The transition material is from a heterogeneous material to a homogeneous materialat higher level requires statistically homogeneous material, in other words, a simple of an appropriate size called representative volume elements(RVE). This subsection provides a brief introduction to micromechanics and homogenization in linear elasticity. It is well known that a material, e.g., cement paste, is regarded as macro-homogeneous, but micro-heterogeneous body filling a RVE[Biot, 1955; Zaoui, 2002], which is fulfilled with the separation of scales requirement[Dormieux*et al.*, 2006; Salenon, 2001; Zaoui, 1997; Pichler*et al.*, 2009]. As shown in Figure 1, the characteristic lengths of RVE need to be defined according to (a) to be representative, it needs to be significantly larger than characteristic dimensions , where ** **stands for the characteristic length of microheterogeneities within the RVE, and

这篇文章涉及工科的问题，如果由好写手去写，查文献软件做数据怎么也得一周时间连续工作才能完成。但是，如果仅仅只看了题目，贪图便宜，随便在中国国内找个二本学生网上找个类似的中文Assignment随便翻一下也能交差。

最可怕的在于，客户对这一切并不知道。初步交稿说不定看看还觉得很好。然后出分的时候，他傻眼了，他也许觉得这是一个意外。为什么呢？

答案冥冥之中早有注定，价格战的背后是一场分数的博弈。

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