With the increasing use of composites in medicine, the use of biocompatible composites of short fibers as fixtures for broken bones has also found its place. This paper uses damage mechanics to optimize a composite fixture for a wrist fracture - a fracture of the distal radius - to delay damage in the fixture. To model the fixture behavior, a model with two stages of homogenization as well as continuous Lemaitre damage is used to predict the damage. In this modeling, Mori-Tanaka homogenization is used to homogenize the grain hardness modulus and the Voight model is used for homogenizing the composite. The introduced algorithm for the numerical implementation of the two-stage homogenization model could easily be used to predict damage in other short fiber composites. After verifying the model presented in a valid fixture, the geometric shape of this fixture has been optimized. The research results show the proposed model; It is an efficient model for predicting damage in short fiber composite plates and can be used to optimize fixtures without clinical and experimental tests.

The Continuum Damage Mechanics is a branch of applied mechanics that predicts the initiation of cracks in metal forming processes. In this paper, a modified ductile damage model is applied to predict initiation of the micro-void as a central burst along the bar axis during the forward extrusion. The implicit integration scheme of the coupled constitutive equations is presented. The effects of various process parameters including die semi-angle, reduction in area, friction coefficient and material ductility on central bursts are discussed. To verify the quality of simulations, numerical predictions were compared with published experimental results, and good agreement was observed.

Ductile failure is one of the subjects that many researches on which have been done, up to now. X100 pipeline steel is one of the recently developed materials for gas transfer pipe production. Regarding the metallurgical structure and different treatments, this material has a correct balance between strength (yield stress of 690MPa) and toughness (150% true strain at failure in simple tension). Moreover this material is severely anisotropic in plastic deformation.In this article Continuum Damage Mechanics (CDM), which is a new method with high capabilities, is used to predict the failure of X100 steel. At first the CDM model is modified to take into account the effect of anisotropic plasticity (Hill quadratic plasticity), then according to damage formulations, an FE subroutine is developed to model the failure behavior of this material. Material parameters which are needed in damage and plasticity models are extracted from a series of experiments. Experiments and simulations on smooth and notched specimens show that this model has a good capability to predict the failure in different loading conditions.

Continuum Damage Mechanics (CDM) is a powerful tool to solve problems such as large plastic deformation, Where the fracture mechanics is unable to analysis of its effects. Continuum damage mechanics in terms of the internal variable theory of thermodynamics is derived and based on the experimental results on material properties is developed. As regards, Aluminum has an important role in designing and construction of aerospace structures and devices, since its density and strength are suitable to aerospace applications. Al 5083 is one of the most widely used materials in the construction of missiles, space vehicles and sounding rocket structure. In this paper, the continuum damage mechanics principles are studied. Nucleation, development and propagation of damage in Al 5083 are investigated based on Bonora model as a non-linear model. FE simulation of material behavior during failures is carried out by ABAQUS software package and USDFLD subroutine. The results are validated with experimental tests. This comparison shows that the simulation results are agree with that of experimental tests, also the Bonora model can be used of damage modeling of AL 5083.

The component operating at elevated temperature usually fails because of creep damage resulted from formation, growth and combination of micro-voids. To predict the creep life, ia number of methods have been suggested. One of them is Monkman-Grant (M-G) relationship that is widely applied in engineering problems.In order to adjust the variation between the empirical and theoretical results and because of the importance of the third phase of creep this model has been modified. In this work, the M-G method has been modified to give a more accurate result by using the Continuum Damage Mechanics and then, the creep life of IN738LC has been determined.The results show that the predicted creep life determining from the modified model demonstrates good agreement with that of the Koul-Castillo model due to pay more attention to the third stage of creep in the presented study model.

In general, materials include micro-cracks and small holes which is created during the manufacturing process. The growth of these micro-cracks leads to degradation of mechanical properties and resulting in deterioration of the materials. Continuum damage mechanics is the new field of failure criteria which survey the behavior and responses of weakened material during the complete process of deterioration of material. This method defines the damage growth with an internal variable and can be used to predict the failure behavior of many materials such as metals, composites, polymers, and so on. Shape memory alloys have unique features, such as, having memorable properties, being super elastic and being energy absorber, which led to new applications in science and engineering research. Super elastic property accompanies with a lot of energy absorption during creating a Hysteresis loop. In this research, we examine mechanical behavior of materials reinforced with smart alloy in the context of environmental damage mechanics. Simulation and experimental results were very close. The considered structure is a notched piece of aluminum which is reinforced by the smart alloy. This material is notched because when the smart alloy reaches to its maximum reversible strain, damage variable reaches to its critical value due to the stress concentration. Accordingly, in this case, the effect of existence of the smart alloy is studied to find how it reduces the growing of the damage. Simulation of the mentioned structure is performed with Finite Element Analysis, where the structure was modeled under longitudinal loading. UMAT code of Lemaiter model, was developed for behavioral properties with damaged aluminum, UMAT code of Brinson model was used for behavioral properties of shape memory alloy. Simulation results suggest that different behavioral aluminum with aluminum reinforced by SMA. Existence of smart alloy on the aluminum substrate reduces the damage evolution and the structure fails in higher loadings. Also, the simulation results showed that reinforcing materials such as aluminum with shape memory alloys, up to the failure, are suitable choices for cyclic loading.

In this paper, the reliability of rectangular plates without holes and containing a central circular hole under static tensile load has been studied. To investigate the initiation and evolution of damages, continuum damage mechanics approach together with finite element has been used. Constitutive equations with scalar damage have been obtained for the plate and implemented in finite element code, ABAQUS.  To analyze the probability of failure the first/second order reliability methods have been used and then, limit state function and random variables according to the continuum damage mechanics model obtained. The force-displacement curves for various sizes of the hole are obtained. With the addition of a central hole in a plate with a diameter of 2 to 10 mm, failure load is reduced by approximately 60 to 80%, which is consistent with the concepts of stress concentration. Finally, the probability of failure of each plate with different hole sizes is approximated and sensitivity analysis on the coefficient of variation is performed. The reliability of the specimen with a diameter of 10 mm has the lowest value, while the plate without a hole has the highest value and among the random variables, the critical damage is the most effective one in reliability.

According to the structure of sandwich panels, different failure modes occur during periodic loading in these structures. When the effect of these modes on each other is considered the predictions will be more accurate. In this research, a new tool presented with the help of the combination of USDFLD and UMAT subroutine in the Abaqus software to see the mutual fatigue effect of the face and the delamination between the face and the core using the existing models. This tool is used to fatigue analysis of a sandwich beam with a PVC core with different stiffness and AS4/3501-6 composite faces with [0]4, [90]4 layup. The delamination between the face and the core is analyzed by cohesive zone model and the face fatigue by an energy-based model simultaneously. The results showed that with the increase of the core stiffness, the delamination between the face and the core, caused by fatigue, begins later and moves towards the free edges of the plate. It was also observed that the failure mode that controls the life of this structure is the delamination between the face and the core. The results show the decrease in the growth rate of the damage parameter in the cohesive zone for specified element, increase of the crack growth rate and growth rate of the damage parameter in the face during loading.

As experiments show, there is nonlinear behavior of carbon nanotubes after exceeding a certain boundary surface while loading continues. Avoiding being involved in molecular dynamics methods and quantum mechanics approach, a continuum macro mechanics based method is employed to predict the nonlinear behavior of bonding forces in carbon nanotubes. Both analytical and numerical approaches, assuming elasto-plastic behavior of tubes are considered in this research. The presented results are well compared with the test as well as molecular dynamics results. Finally, the limitation and advantages of the proposed method are pointed out.