Papers by Keyword: Damage Mechanics

Abstract: The concept of complex damage variables is introduced in this work. These damage variables have both real and imaginary parts. They are introduced not to use them in practical applications but to try to derive a direct relationship between the damage due to cross-sectional area reduction and the damage due to elastic stiffness degradation. In addition this concept can provide an insight in addressing the concept of healing that the authors have extensively published as well as the concept of undamageable materials. Toward this goal some success is achieved in the sense that some complicated relationships between the two damage processes are formulated. These relationships and the complex variable approach are novel ideas in Continuum Damage Mechanics. Throughout the formulation the hypothesis of strain equivalence is used in order to simplify the mathematical equations. This work can be extended and generalized by substituting the hypothesis of energy equivalence but this will complicate the equations unnecessarily.

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After surrounding rock is disturbed by some damage form a loosen circle in surrounding rocks of a roadway, in order to solving the range of loosen circle, mechanical mechanism of loosen circle was discussed on the basis of damage mechanics and loosen circle radius calculation formula proposed. This work has some certain reference for roadway support design.

Abstract: The low cycle fatigue damage of turbine disc which is made of GH901 material is systematic analyzed and studied in the article that is based on the theory of continuum damage mechanics and fatigue testing, we improved the common Lemaitre’s low cycle fatigue damage mechanics model, the damage evolution law that the model describes is in good agreement with the test results throughout the course of the fatigue damage. The simplified analysis method for low cycle fatigue damage evolution and life prediction is proposed based on the GH901 low cycle damage features, the practical method of getting damaged material’s constants by existing data is proposed as well.

Abstract: As an exploration and extension of load/unload response ratio theory, unload/ load response ratio theory (ULRR for short) is introduced firstly, and the relationship between ULRR (Y′) and elastic modulus (E for short) is obtained. Based on the basic theory of damage mechanics,the relationship between ULRR and damage variable (D for short) is set up and analyzed with the relationship between E and D. The unloading and loading experiments on a two-story structure carried out in the University of Naples in Italy are introduced;and calculated damage variable is compared with that calculated by Zhang Langping who put forward Weibull distribution as random distribution function. The results show that damage variable of the structure keep highly consistent with calculations of these two methods. Therefore, the relationship between Y′and D provides a new approach to a health assessment to catastrophic failure of large-scale structures and prediction of engineering.

Abstract: In this work, a new damage model for mixed-mode fracture in the scope of the discrete crack approach is introduced. An energy-based internal damage variable is adopted. In the model, deformation-driven loading surfaces are defined and the dual loading surfaces in the traction space are derived. Under proportional loading, it is found that the constitutive relationship is symmetric. Further enrichment of the energy-based variable on the traction field is also introduced, allowing for a better approximation of: i) the limit surface defined in traction space and ii) non-proportional loading. However, in this case symmetry of the constitutive tensor is lost.

Abstract: Fatigue failure of sucker rod can occur under the effect of alternating load, and results in failure of sucker rod. In this paper, the damage mechanics theory is applied to the fatigue damage of sucker rod on the study, establish the fatigue damage evolution equation of sucker rod, and the damage mechanics-finite element method is adopted to solve fatigue damage of sucker rod, obtain change law of stress field, strain field and fatigue damage field of sucker rod, and carry out fatigue damage cycles of sucker rod. The study has a certain theoretical significance and practical significance on the rational use of sucker rod, the decrease of sucker rod fracture accident and the improvement of overall economic benefits in oilfield development.

Abstract: Waste tires create big problem in the world as for their utilization. One domain in which this material is able to found promising application is civil engineering. The waste tires additive in the concrete manufacturing leads to change of mechanical properties such as: Young modulus, compressive strength, fracture toughness, energy absorption, brittleness, water absorption etc. It was partly reported in the literature only for the plain concrete. There is no investigations for a lean concrete - the material which has potential applications as a subgrade of roads. The aim of this paper is to investigate the importance of the rubber particles addition in the lean concrete production as for modification of the basic mechanical properties and further degradation of the material due to mechanical loading. The new technology of compaction of the concrete was elaborated to perform basic test: cyclic uniaxial compression and cyclic bending. In order to describe gradual degradation of the rubberized lean concrete a scalar damage parameter D related to loading history was proposed. The current value of the elastic modulus was expressed as E=E_o(1-D), where E_o denotes the initial value of the Young’s modulus. The paper includes also a numerical model of the beam made of the rubberized lean concrete, which is subjected to 3-point bending deformation. The stress distribution in this beam is highly non-homogeneous with visible stress concentrations around the rubber particles.

Abstract: The paper deals with identifying of the damage model for a bundle of T300 and AS4D fibers under tensile load. The damage model is implemented in ANSYS for a one-dimensional bar element and obtained the strain-stress response of a bundle of fibers. The delamination of laminate plate, which consists of unidirectional fiber reinforced layers, is investigated. The methodology adopts the first-order shear laminate plate theory and fracture and contact mechanics. Within the interface modeling there are calculated the individual components of energy release rate along the lamination front. Numerical results are given for mixed mode delamination problems. Numerical example is done by the commercial ANSYS code.

Abstract: We develop a novel constitutive modeling approach for the analysis of fracture propagation in quasi-brittle materials using the Material Point Method. The kinematics of constitutive models is enriched with an additional mode of localized deformation to take into account the strain discontinuity once cracking has occurred. The crack details therefore can be stored at material point level and there is no need to enrich the kinematics of finite elements to capture the localization caused by fracturing processes. This enhancement also removes the drawback of classical smeared crack approach in producing unphysical snapping back constitutive responses when the spatial resolution is not fine enough. All these facilitate the implementation of the new approach in the Material Point Method for analysis of large scale problems. Numerical examples of fracture propagation are used to demonstrate the effectiveness and potentials of the new approach.

Abstract: Currently, researches on the gravity dam deep and shallow anti-sliding stability mainly focus on the analysis method and instability criterion, while the studies on specifically test the breakage of gravity dams due to weakening foundation rock mass and structural planes under loading are rare. Based on damage mechanics theory, this paper established a numerical model that analyzed the damage failure process of dam foundation rock mass. Taking two typical gravity dam models as the study objects, the damage processes of the dam foundations were simulated dynamically. Additionally, a comparison with other two traditional methods further validated the correctness and feasibility of the numerical model. In sum, the study findings point out that the numerical model is not only applicable to the study of the breakage mechanism of dam foundation rock mass, but also can be used as a new method to analyze problems related to deep anti-sliding stability of gravity dams.