A Numerical Study of Crack Mixed Mode Model in Concrete Material Subjected to Cyclic Loading.

In quasi-brittle materials such as concrete, numerical methods are frequently used to simulate the crack propagation for monotonic loading. However, further research and action are required to better understand the fracture properties under cyclic loading. For this purpose, in this study, we present numerical simulations of mixed-mode crack propagation in concrete using the scaled boundary finite element method (SBFEM). The crack propagation is developed based on a cohesive crack approach combined with the thermodynamic framework of a constitutive concrete model. For validation, two benchmark crack-mode examples are modelled under monotonic and cyclic loading conditions. The numerical results are compared against the results from available publications. Our approach revealed good consistency compared to the test measurements from the literature. The damage accumulation parameter was the most influential variable on the load-displacement results. The proposed method can provide a further investigation of crack growth propagation and damage accumulation for cyclic loading within the SBFEM framework.

Modeling Cyclic Crack Propagation in Concrete Using the Scaled Boundary Finite Element Method Coupled with the Cumulative Damage-Plasticity Constitutive Law.

Many concrete structures, such as bridges and wind turbine towers, fail mostly due to the fatigue rapture and bending, where the cracks are initiated and propagate under cyclic loading. Modeling the fracture process zone (FPZ) is essential to understanding the cracking behavior of heterogeneous, quasi-brittle materials such as concrete under monotonic and cyclic actions. The paper aims to present a numerical modeling approach for simulating crack growth using a scaled boundary finite element model (SBFEM). The cohesive traction law is explored to model the stress field under monotonic and cyclic loading conditions. In doing so, a new constitutive law is applied within the cohesive response. The cyclic damage accumulation during loading and unloading is formulated within the thermodynamic framework of the constitutive concrete model. We consider two common problems of three-point bending of a single-edge-notched concrete beam subjected to different loading conditions to validate the developed method. The simulation results show good agreement with experimental test measurements from the literature. The presented analysis can provide a further understanding of crack growth and damage accumulation within the cohesive response, and the SBFEM makes it possible to identify the fracture behavior of cyclic crack propagation in concrete members.

A New Efficient Approach to Simulate Material Damping in Metals by Modeling Thermoelastic Coupling.

The realistic prediction of material damping is crucial in the design and dynamic simulation of many components in mechanical engineering. Material damping in metals occurs mainly due to the thermoelastic effect. This paper presents a new approach for implementing thermoelastic damping into finite element simulations, which provides an alternative to computationally intensive, fully coupled thermoelastic simulations. A significantly better agreement between simulation results and experimental data was achieved, when compared with the empirical damping values found in the literature. The method is based on the calculation of the generated heat within a vibration cycle. The temperature distribution is determined by the mechanical eigenmodes and the energy converted into heat, and thus dissipated, is calculated. This algorithm leads to modal damping coefficients that can then be used in subsequent analyses of dynamically excited oscillations. The results were validated with experimental data obtained from vibration tests. In order to measure material damping only, a test setup excluding friction and environmental influences was developed. Furthermore, comparisons with fully coupled thermoelastic simulations were performed. It was clear that the new approach achieved results comparable to those of a computationally expensive, coupled simulation with regard to the loss factors and frequency response analyses.

Numerical simulation techniques to study the structural response of the human chest following median sternotomy.

BACKGROUND: The optimal closure technique of median sternotomy remains controversial. The objective of this study was to analyze the structural response of the separated sternum using computer-based numerical discretization techniques, such as finite element methods. METHODS: Thoracic computer tomographic scans (2.5-mm slices) were segmented, analyzed by image processing techniques, and transferred into a three-dimensional finite element model. In a first approach a linear elastic material model was used; neglecting nonlinear and damage effects of the bones. The influence of muscles and tendons was disregarded. Nonlinear contact conditions were applied between the two sternal parts and between fixation wires and sternum. The structural response of this model was investigated under normal breathing and asymmetric leaning on one side of the chest. Displacement and stress response of the segmented sternum were compared regarding two different closure techniques (single loop, figure-of-eight). RESULTS: The obtained results revealed that for the normal breathing load case the single loop technique is capable of clamping the sternum sufficiently, assuming that the wires are prestressed. For asymmetric loading conditions, such as leaning on one side of the chest, the figure-of-eight loop can substantially reduce the relative longitudinal displacement between the two parts compared with the single loop. CONCLUSIONS: The application of numerical simulation techniques using complex computer models enabled the determination of structural behavior of the chest regarding the influence of different closure techniques. They allowed easy and fast modifications and therefore, in contrast to a real physical model, in-depth parameter studies.