Literature study report of plasticity induced anisotropic damage modeling for forming processes

A literature study report covering the topics; micromechanics of damage, continuum damage mechanics (gurson model and effective variable concept) and the dependence of damage on strain rate and temperature

Progressive failure methodologies for predicting residual strength and life of laminated composites

Two progressive failure methodologies currently under development by the Mechanics of Materials Branch at NASA Langley Research Center are discussed. The damage tolerance/fail safety methodology developed by O'Brien is an engineering approach to ensuring adequate durability and damage tolerance by treating only delamination onset and the subsequent delamination accumulation through the laminate thickness. The continuum damage model developed by Allen and Harris employs continuum damage laws to predict laminate strength and life. The philosophy, mechanics framework, and current implementation status of each methodology are presented

Basic concepts and models in continuum damage mechanics

In this paper, we present some basic elements of macroscopic modelling of damage. We then recall the general approach of continuum damage based on the thermodynamics of irreversible processes and its application to isotropic damage modelling. The study of damage induced anisotropy is treated by considering a second order tensorial damage variable. Finally, we present an original macroscopic approach through which is addressed the question of unilateral effects due to the microcracks closure

Modeling of ductile damage using numerical analyses on the micro-scale

The presentation deals with a continuum damage model which has been generalized to take into account the effect of stress state on damage criteria as well as on evolution equations of damage strains. It is based on the introduction of damaged and corresponding undamaged configurations. Plastic behavior is modeled by a yield criterion and a flow rule formulated in the effective stress space (undamaged configurations). In a similar way, damage behavior is governed by a damage criterion and a damage rule considering the damaged configurations. Different branches of the damage criterion are considered corresponding to various damage mechanisms depending on stress intensity, stress triaxiality and the Lode parameter. Experiments with carefully designed specimens are performed and the test results are used to identify basic material parameters. However, it is not possible to determine all parameters based on these tension and shear tests. To be able to get more insight in the complex damage behavior under different loading conditions, additional series of micro-mechanical numerical analyses of void containing unit cells have been performed. These finite element calculations on the micro-level cover a wide range of stress triaxialities and Lode parameters in the tension, shear and compression domain. The numerical results are used to show general trends, to develop equations for the stress-statedependent damage criteria, to propose evolution equations of damage strains, and to identify parameters of the continuum model

Development of methologies to study the damage tolerance of aeronautical and aerospace composite structures

Mechanics of Advanced Materials research group (Department of Continuum Mechanics and Structural Analysis) of the University Carlos III of Madrid (Spain) offers their experience in the analysis and modelization of high and low velocity impact behaviour and damage tolerance of composite structures

Post-hoc derivation of SOHO Michelson doppler imager flat fields

<p><b>Context:</b> The SOHO satellite now offers a unique perspective on the Sun as it is the only space-based instrument that can provide large, high-resolution data sets over an entire 11-year solar cycle. This unique property enables detailed studies of long-term variations in the Sun. One significant problem when looking for such changes is determining what component of any variation is due to deterioration of the instrument and what is due to the Sun itself. One of the key parameters that changes over time is the apparent sensitivity of individual pixels in the CCD array. This can change considerably as a result of optics damage, radiation damage, and aging of the sensor itself. In addition to reducing the sensitivity of the telescope over time, this damage significantly changes the uniformity of the flat field of the instrument, a property that is very hard to recalibrate in space. For procedures such as feature tracking and intensity analysis, this can cause significant errors.</p> <p><b>Aims:</b> We present a method for deriving high-precision flat fields for high-resolution MDI continuum data, using analysis of existing continuum and magnetogram data sets.</p> <p><b>Methods:</b> A flat field is constructed using a large set (1000-4000 frames) of cospatial magnetogram and continuum data. The magnetogram data is used to identify and mask out magnetically active regions on the continuum data, allowing systematic biases to be avoided. This flat field can then be used to correct individual continuum images from a similar time.</p> <p><b>Results:</b> This method allows us to reduce the residual flat field error by around a factor 6-30, depending on the area considered, enough to significantly change the results from correlation-tracking analysis. One significant advantage of this method is that it can be done retrospectively using archived data, without requiring any special satellite operations.</p&gt

A differential CDM model for fatigue of unidirectional metal matrix composites

A multiaxial, isothermal, continuum damage mechanics (CDM) model for fatigue of a unidirectional metal matrix composite volume element is presented. The model is phenomenological, stress based, and assumes a single scalar internal damage variable, the evolution of which is anisotropic. The development of the fatigue damage model, (i.e., evolutionary law) is based on the definition of an initially transversely isotropic fatigue limit surface, a static fracture surface, and a normalized stress amplitude function. The anisotropy of these surfaces and function, and therefore the model, is defined through physically meaningful invariants reflecting the local stress and material orientation. This transversely isotropic model is shown, when taken to it's isotropic limit, to directly simplify to a previously developed and validated isotropic fatigue continuum damage model. Results of a nondimensional parametric study illustrate (1) the flexibility of the present formulation in attempting to characterize a class of composite materials, and (2) the capability of the formulation in predicting anticipated qualitative trends in the fatigue behavior of unidirectional metal matrix composites. Also, specific material parameters representing an initial characterization of the composite system SiC/Ti 15-3 and the matrix material (Ti 15-3) are reported

New tension-compression damage model for complex analysis of concrete structures

A new damage model, based on continuum damage mechanics and simulating the opening, closing, and reopening of cracks in concrete using only one surface of discontinuity, is proposed in this article. The model complies with the thermodynamics principles of nonreversible, isothermal, and adiabatic processes. Two scalar internal variables have been defined: a tensile damage variable d+d+ and a compressive damage variable d-d-; the threshold of damage is controlled by only one surface of discontinuity and a new parameter controlling the damage variable that should be activated. This new parameter represents the ratio of tensile stress to compressive stress in the damaged material. The continuity of response under complex loads, which is one of the aims of this work, is ensured. An adequate response under different types of loads leads to the conclusion that the proposed model provides a powerful tool to numerically analyze reinforced concrete structures. Validation and illustrative examples are included in the article.Peer ReviewedPostprint (author's final draft

Differential continuum damage mechanics models for creep and fatigue of unidirectional metal matrix composites

Three multiaxial isothermal continuum damage mechanics models for creep, fatigue, and creep/fatigue interaction of a unidirectional metal matrix composite volume element are presented, only one of which will be discussed in depth. Each model is phenomenological and stress based, with varying degrees of complexity to accurately predict the initiation and propagation of intergranular and transgranular defects over a wide range of loading conditions. The development of these models is founded on the definition of an initially transversely isotropic fatigue limit surface, static fracture surface, normalized stress amplitude function and isochronous creep damage failure surface, from which both fatigue and creep damage evolutionary laws can be obtained. The anisotropy of each model is defined through physically meaningful invariants reflecting the local stress and material orientation. All three transversely isotropic models have been shown, when taken to their isotropic limit, to directly simplify to previously developed and validated creep and fatigue continuum damage theories. Results of a nondimensional parametric study illustrate (1) the flexibility of the present formulation when attempting to characterize a large class of composite materials, and (2) its ability to predict anticipated qualitative trends in the fatigue behavior of unidirectional metal matrix composites. Additionally, the potential for the inclusion of various micromechanical effects (e.g., fiber/matrix bond strength, fiber volume fraction, etc.), into the phenomenological anisotropic parameters is noted, as well as a detailed discussion regarding the necessary exploratory and characterization experiments needed to utilize the featured damage theories

Modeling and experimental investigations of the stress-softening behavior of soft collagenous tissues

This paper deals with the formulation of a micro-mechanically based dam-age model for soft collagenous tissues. The model is motivated by (i) a sliding filament model proposed in the literature [1] and (ii) by experimental observations from electron microscopy (EM) images of human abdominal aorta specimens, see [2]. Specifically, we derive a continuum damage model that takes into account statistically distributed pro- teoglycan (PG) bridges. The damage model is embedded into the constitutive framework proposed by Balzani et al. [3] and adjusted to cyclic uniaxial tension tests of a hu- man carotid artery. Furthermore, the resulting damage distribution of the model after a circumferential overstretch of a simplified arterial section is analyzed in a finite element calculation