Authors: Vladislav Kozák, Ivo Dlouhý, Zdeněk Chlup
Abstract: The micromechanical modelling encounters a problem that is different from basic
assumptions of continuum mechanics. The material is not uniform on the microscale level and the
material within an element has its own complex microstructure. Therefore the concept of a
representative volume element (RVE) has been introduced. The general advantage, compared to
conventional fracture mechanics, is that, in principle, the parameters of the respective models
depend only on the material and not on the geometry. These concepts guarantee transferability from
specimen to components over a wide range of dimensions and geometries. The prediction of crack
propagation through interface elements based on the fracture mechanics approach (damage) and
cohesive zone model is presented. The cohesive model for crack propagation analysis is
incorporated into finite element package by interface elements which separations are controlled by
the traction-separation law.
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Authors: Yin Fang Jiang, Lei Fang, Zhi Fei Li, Zhen Zhou Tang
Abstract: As a new lightweight material and new technique,Tailor Rolled Blanks has a good prospect in energy-saving environmental protection and the future development of the automobile industry, formability window of Tailor Rolled Blanks at blank-holder force has important practical significance. Based on the research of a square box TRB, the paper proposes a theory of TRB’ formability window, also with the usage of an ABACUS finite element software to simulate the TRB sheet in the course of the critical wrinkling BHF curve and critical fracture BHF curve, to establish TRB formability window under the condition of blank holder force. The results not only show that the square box of TRB has the security zone in the deep drawing process, but also has got the wrinkling and fracture areas of the square box.
488
Authors: Zhi Fang Zhao, Qiu Yu Wang, Zhi Hua Yang, Yang Yang
Abstract: The softening curves of four groups specimens with different sizes were obtained by inverse analysis based on the fictitious crack model（FCM）and the P-CMOD curve achieved by a three-point bending notched beam (TPB) test. According to the softening curves obtained by inverse analysis, size effect of softening curves was investigated，which shows both the tail of calculated softening curve, namely the maximum crack width wc and fracture energy GF have an increasing trend with the increase of the specimen size, but no longer to increase when the specimen size attains to a certain level.
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Authors: Faramarz Fereshteh Saniee, Farzan Barati
Abstract: One of the ways for determination of flow curves is the application of a ring test. Using this method, friction in the interface between the die and the specimen leads to a bulging of the sample and thereby to an inhomogeneous stress and strain state. The calculation of the flow stress from experimentally determined force–displacement curves implies a uniaxial stress state, but this will produce an error because of the above-mentioned bulging, when friction occurs. One method of avoiding these sources of error is to use the sigmoid curves, but the sigmoid curves are varied by the change of temperature and strain rate. Calculations of numerical sigmoid curves were done by the use of an iterative procedure, applying a corrective function. The paper presents a complete investigation of the AZ41 magnesium alloy sigmoid curves at temperature ranging between 473 K and 513 K and strain rates ranging between 0.025 s-1 and 0.00025 s-1 . Ring tests are used to determine the numerical sigmoid curves sensitivity to temperature and strain rate.
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Abstract: In order to find out the influence of geometric characteristics, distribution and combination condition of mineral aggregates on mixture properties, the single and multi aggregates were built using finite element method and the mechanical properties of aggregates was discussed. Then comparison analysis was carried out for three representative asphalt mixture structures with different gradations. Finally the optimal gradation curve was obtained. Simulation results are as follows: extreme values or damage of stress was likely to emergence on the interface between mortar and aggregate; the impact on the equivalent stress of aggregate space in vertical direction is greater than in horizontal direction; in comparison with "framework-pore" structure, the "suspend-dense" structure and "framework-dense" structure had better shear resistance behavior and load-carrying capacity. The results shows that the macroscopical carrying capacity of asphalt mixtures was determined by the microcosmical mechanical properties of aggregates, and it was a new mehtod for researching mechanical behavior owing to internal nonuniformity of asphalt mixture in future.
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