A mechanism!based theory of strain gradient plasticity "MSG# is proposed based on a multiscale framework linking the microscale notion of statistically stored and geometrically necessary dislocations to the mesoscale notion of plastic strain and strain gradient[ This theory is motivated by our recent analysis of indentation experiments which strongly suggest a linear dependence of the square of plastic ~ow stress on strain gradient[ While such linear dependence is predicted by the Taylor hardening model relating the ~ow stress to dislocation density\ existing theories of strain gradient plasticity have failed to explain such behavior[ We believe that a mesoscale theory of plasticity should not only be based on stressÐstrain behavior obtained from macroscopic mechanical tests\ but should also draw information from micromechanical\ gradient!dominant tests such as micro!indentation or nano!indentation[ According to this viewpoint\ we explore an alternative formulation of strain gradient plasticity in which the Taylor model is adopted as a founding principle[ We distinguish the microscale at which dislocation interaction is considered from the mesoscale at which the plasticity theory is formulated[ On the microscale\ we assume that higher order stresses do not exist\ that the square of ~ow stress increases linearly with the density of geometrically necessary dislocations\ strictly following the Taylor model\ and that the plastic ~ow retains the associative structure of conventional plasticity[ On the mesoscale\ the constitutive equations are constructed by averaging microscale plasticity laws over a representative cell[ An expression for the e}ective strain gradient is obtained by considering models of geometrically necessary dislocations associated with bending\ torsion and 1!D axisymmetric void growth[ The new theory di}ers Corresponding author[ Fax] 990 304 612 0667^e!mail] gaoÝam!sun1[stanford[edu from all existing phenomenological theories in its mechanism!based guiding principles\ although the mathematical structure is quite similar to the theory proposed by Fleck and Hutchinson[ A detailed analysis of the new theory is presented in Part II of this paper[ Þ 0888 Elsevier Science Ltd[ All rights reserved[

H. Gao

Y. Huang

W.D. Nix

J.W. Hutchinson

Journal of the Mechanics and Physics of Solids

目的是发表关于固体力学的最高质量和具有持久意义的研究。范围很广，从力学的基本概念到新现象和应用的分析。固体被广义地解释为包括硬质和软质材料以及天然和合成结构。该方法可以是理论的、实验的或计算的。这项研究活动位于工程科学和应用数学、材料科学、生物力学、应用物理学和地球物理学的相关领域。该杂志由 RODNEY HILL 于 1952 年创立，他是其主编直至 1968 年。该杂志感兴趣的主题随着主题的发展而发展，但其基本精神保持不变：发表与固体力学有关的最高质量的研究。因此，重点放在基于理论、实验或计算方法的力学基本概念的发展和这些概念的新应用上，利用工程科学的各个分支以及应用数学、材料科学、结构工程、应用物理学和地球物理学。该杂志的主要目的是促进对所有固体材料（技术和自然）的变形和机械失效过程以及这些过程及其潜在物理机制之间的联系的科学理解。从这个意义上说，期刊的内容应该反映学科在分析、实验观察和数值模拟方面的现状。为了实现这一目标，除了描述他们的工作细节外，鼓励作者考虑他们对力学领域的贡献的重要性及其结果的影响。

The Journal of the Mechanics and Physics of Solids aims to publish high-quality and enduring research in the field of solid mechanics. Its scope is broad, covering analyses from fundamental concepts of mechanics to new phenomena and applications. Solids are broadly defined to include both hard and soft materials, as well as natural and synthetic structures. The methods of study can be theoretical, experimental, or computational. This research activity spans relevant fields such as engineering science, applied mathematics, materials science, biomechanics, applied physics, and geophysics. The journal was founded by RODNEY HILL in 1952, who served as its editor until 1968. While the topics of interest have evolved with the field, the journal's fundamental spirit remains unchanged: to publish high-quality research related to solid mechanics. Thus, the focus is on the development of fundamental concepts of mechanics based on theoretical, experimental, or computational methods, and the new applications of these concepts, utilizing various branches of engineering science, as well as applied mathematics, materials science, structural engineering, applied physics, and geophysics. The primary goal of the journal is to promote a scientific understanding of the deformation and mechanical failure processes of all solid materials (both technical and natural) and the connections between these processes and their potential physical mechanisms. In this sense, the content of the journal should reflect the current state of the discipline in terms of analysis, experimental observation, and numerical simulation. To achieve this goal, authors are encouraged to consider the significance of their contributions to the field of mechanics and the impact of their results, in addition to detailing their work.

《Journal of the Mechanics and Physics of Solids》旨在发表高质量且具有持久意义的固体力学研究。其研究范围广泛，涵盖从力学基本概念到新现象和应用的分析。固体的定义广泛，包括硬质和软质材料以及天然和合成结构。研究方法可以是理论的、实验的或计算的。这项研究活动涉及工程科学、应用数学、材料科学、生物力学、应用物理学和地球物理学等相关领域。该杂志由RODNEY HILL于1952年创立，并担任主编直到1968年。随着主题的发展，杂志感兴趣的研究领域也在不断扩展，但其核心宗旨始终如一：发表与固体力学相关的高质量研究。因此，重点在于基于理论、实验或计算方法的力学基本概念的发展，以及这些概念的新应用，涉及工程科学的各个分支，以及应用数学、材料科学、结构工程、应用物理学和地球物理学。该杂志的主要目的是促进对所有固体材料（包括技术和自然材料）的变形和机械失效过程的科学理解，以及这些过程与潜在物理机制之间的联系。因此，期刊内容应反映该学科在分析、实验观察和数值模拟方面的最新进展。为实现这一目标，除了详细描述研究工作外，鼓励作者考虑其研究对力学领域的贡献及其结果的影响。

Category	Quartile
工程技术	2
工程技术, 材料科学综合	2
工程技术, 力学	2
工程技术, 物理凝聚态物理	2

Mechanism-based strain gradient plasticity— I. Theory

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Category	Quartile
PHYSICS, CONDENSED MATTER	2