Numerical simulation of chloride diffusion through high-performance binding systems such as limestone-calcined clay cement (LC3) and its comparison to control and fly ash modified concretes is ...discussed. The simulation framework considers the pore structure of concrete, the concentration-dependence of diffusion coefficient, and Freundlich binding. The LC3 concrete and the companion fly ash concrete exhibit similar service lives (~8× control mixture), despite the LC3 system having a reduced clinker factor than the fly ash concrete (~0.5, as opposed to 0.7). The diffusion model is augmented with a scalar isotropic damage variable that accounts for random distribution of microcracks under fatigue loading (e.g., in a bridge deck). The impact of damage on service life at different stress levels, for the different concretes is elucidated. The modeling approach can be used to evaluate the influence of binder composition and damage on effective service life of chloride-exposed concrete structures, thereby aiding in binder selection.
The presence of hierarchical microstructures in natural materials, such as connective tissues, makes them possess exceptional mechanical performance and undergo complex damage behaviors. Accordingly, ...in this study, a structure-based unit cell model (UCM) in which controllable irregular crimped fiber is embedded into soft matrix is constructed for the analysis of microstructural effects. An anisotropic hyperelastic constitutive model enhanced with different damage parameters is applied in finite element program, and the effects of damage parameters on the mechanical responses of fibrous soft tissues are investigated. The numerical results indicate that the fiber waviness plays a significant role in determining the stiffness of the tissues and that the microstructure controlled by the fiber crimp amplitude H, waviness χ and number of inflection points ω, mainly determines the fluctuation of the nominal stress–strain curves of these tissues with damaged fibers. In addition, a damage parameter analysis indicates that the attenuation of the strength and amplitude of the stress strongly depend on the strain energy limiter, and the parameter m mainly determines the rate of damage accumulation by the fibers with smaller strain energy limiters. The results of this study deepen the understanding of the mechanical behaviors of such fibrous soft tissues and provides a template for the optimization of structural and material designs for bioinspired composites.
Low‐cycle fatigue of IN 718: Effect of waveform Barat, Kaustav; Sivaprasad, S.; Kar, Sujoy Kumar ...
Fatigue & fracture of engineering materials & structures,
December 2019, 2019-12-00, 20191201, Letnik:
42, Številka:
12
Journal Article
Recenzirano
The influence of various strain waveforms on the low‐cycle fatigue of IN 718 tested at 650°C has been investigated. The straining paths are accompanied by dwell‐induced creep component(s) or unequal ...strain distribution in different portions of cycles reducing strength of material. The investigation intends to clarify mainly mechanistic aspects of relaxation‐fatigue interaction. Features of time‐dependent effect induced by nonpeak dwell and the same accompanied by peak dwell, slow unloading from the peak to a lower strain, and different loading and unloading rates are compared in terms of stress amplitude responses, mean stress relaxation, hysteresis loops, life, and damage parameter DC‐F. Softening is common in all the cases, and degree of softening varies linearly with life. The energy‐based life prediction model has been found to work well for the data, and we have introduced energy fraction–based approach to observe simultaneous contribution from both creep and fatigue on life.
•Developing a hysteresis CZM technique to predict the onset of delamination.•Proposing a new damage model for mixed-mode delamination.•Fatigue damage evolution is captured by gradual degradation of ...interface properties.•Defining a new damage parameter using mix-mode bilinear TSL parameters.•BVP is formulated and FE modeling is presented in the strong form.
A new approach is proposed to predict onset of fatigue-induced delamination in composite laminates under cyclic loading by progressive interface degradation. Based on the hysteresis cohesive zone approach, a new damage parameter is defined to construct an irreversible cohesive zone model. Residual displacement jump is introduced and used along with mixed-mode bilinear traction-separation law parameters for calculating the damage parameter. Fatigue-induced delamination onset is then predicted by proposing a damage criterion. 3-D Finite Element (FE) formulation is developed with proper elements for plies and also proper elements for the interface. Cyclic loading is also simulated mimicked by the MIN-MAX method. The current research is conducted in two parts as Part I and Part II. While this article focuses on the theoretical framework of the developed modeling, the numerical implementation of the modeling and also a comparison of the outputs with experimental observations will be presented in the companion paper as Part II.
With the wide application of SAC305 solders in electronic packaging, it is important to examine their reliability. In this study, uniaxial ratcheting experiments were carried out on SAC305 solders ...with varying loading rates, mean stresses, and stress amplitudes at room temperature. Based on the unified creep–plasticity constitutive model applicable to SAC305 solders, a nonlinear continuum damage mechanics model was established to simulate the whole-life ratcheting behavior. The damage variable was extracted from the elastic modulus decline of the unloading section during the cyclic loading process, and its evolution was based on the damage dissipation potential, which was derived from the theory of continuum damage mechanics. In addition, the normalized life was used to correct the evolution of the damage variable. For a more accurate description of their evolution, the energy method was used to modify the damage evolution parameters under different loading conditions. Finally, the uniaxial ratcheting behavior of SAC305 solder could be accurately described by the modified damage-coupled constitutive model under different loading conditions.
•The damage variable was expressed by the evolution of the unloading elastic modulus.•The speed of damage evolution was distinguished by the plastic strain energy density.•The modified damage model can capture the ratcheting behavior of the solder under different loading conditions.
Based on the critical plane approach and the shear damage model, a new damage parameter based on the strain energy density criterion is proposed. This parameter takes into account the interaction ...between shear stress and hydrostatic stress during microcrack initiation and the contribution of hydrostatic strain energy density to fatigue damage. On this basis, a new multiaxial fatigue life prediction model is established by combining the Basquin-Manson-Coffin equation. The analysis results of five metal materials show that the predicted life correlated well with the experimental observations. The merits of the proposed model are further highlighted by the comparison between the results of the proposed method and those of two fatigue damage prediction models.
•Based on the shear damage model, a new expression of plastic strain energy density is derived.•The damage parameters which can reflect the interaction between different stresses are proposed.•The fatigue life prediction model is established and compared with the prediction results of different models.
•Experimental investigation of multiaxial fatigue of thermoplastics.•Influences of mean stress and stress concentration.•Damage mechanism, multiaxial damage modeling, and life predictions.
...Thermoplastics are used in many industries with many applications and can be manufactured using different processing techniques. Multiaxial loading and non-proportionality between different loading sources are inevitable in many design applications with such materials. In this study, multiaxial fatigue behavior of extruded high density polyethylene (HDPE), polypropylene (PP), and neat polyamide66 (PA66) as well as reinforced with short glass fibers (PA66-G30) was investigated. The effects of mean stress and stress concentration on multiaxial fatigue behavior were also studied. Analytical models to account for these effects based on observed damage mechanism are presented and discussed by the comparing with the experimental data.
This paper presents a comprehensive investigation into non-proportional multi-axial fatigue of welded components by introducing an equivalent structural stress parameter that takes into account of ...load-path non-proportionality in addition to plate thickness and stress state effects. This is accomplished by formulating a “moment of load path” or “MLP” based fatigue damage parameter that provides a consistent treatment of load-path non-proportionality under arbitrary multi-axial loading conditions for which cycle counting can be consistently performed by means of a previously developed path-dependent maximum range (PDMR) cycle counting procedure. To examine its broad applicability and effectiveness, non-proportional multi-axial test data obtained using different components, joint types, and loading conditions from various sources are analyzed using the newly developed equivalent stress parameter. The results show that the new equivalent stress parameter enables not only an effective consolidation of all multi-axial test data (up to about 300 tests) analyzed in this paper into a narrow band, but also the demonstrated transferability between the master S-N curve (dominated by test data under uniaxial cyclic loading conditions) adopted by the 2007 ASME Div 2 and API 579 RP/ASME FFS-1 Codes and the consolidated S-N curve dominated by severe non-proportional multi-axial cyclic loading conditions. As a result of the present development, a unified fatigue evaluation procedure based on the newly proposed effective stress parameter and a single master S-N curve can be implemented for arbitrary cyclic loading conditions regardless of stress multi-axiality or load path proportionality.
•Developing a hysteresis CZM technique to predict the onset of delamination.•Proposing a new damage model for mixed-mode delamination.•Fatigue damage evolution is captured by gradual degradation of ...interface properties.•Defining a new damage parameter using mix-mode bilinear TSL parameters.•BVP is formulated and FE modeling is presented in the strong form.
Delamination onset of composite laminates is investigated under cyclic loading by numerical simulation and fatigue experiments. Firstly, laminated composites in the form of double cantilever beam (DCB) testing specimens are fabricated. Two different manufacturing methods including hand layup and vacuum infusion process are used for fabricated three different lay-up configurations. All specimens are subjected to cyclic loading under displacement control conditions. The variations of compliance versus number of cycles are monitored and recorded during the performed fatigue tests. Then, the developed novel approach in the companion article (Part I) is implemented in this article and numerical simulation is performed to predict the onset of fatigue-induced delamination for the same investigated testing specimens. Results show a good agreement with experimental data. It is observed that the proposed model is able to capture the interfacial degradation by employing a damage evolution law in the onset stage of delamination.
The ongoing studies of the influence of internal defects on fatigue strength of additively manufactured metals adopted an internal crack or notch-like model at which the threshold stress intensity ...factor is the driving mechanism of fatigue failure. The current article highlights a shortcoming of this approach and offers an alternative based on X-ray microcomputed tomography and cyclic plasticity with a hybrid formulation of Chaboche and Armstrong-Frederick material laws. The presented tessellation and geometrical transformation scheme enabled a significantly more realistic morphological representation of internal defects that yielded a cyclic strain within 2% of the experimental values. This means that cyclic plasticity models have an accurate prediction of mechanical properties without repeating a full set of experiments for additively manufactured arbitrary microstructures. The coupling with a material law that is oriented towards the treatment of cyclic hardening and softening enabled more accurate computation of internal stresses under cyclic loading than ever before owing to the maturity of tessellation and numerical tools since then. The resulting stress-strain distributions were used as input to the Fatemi-Socie damage model, based on which a successful calculation of fatigue lifetime became possible. Furthermore, acting stresses on the internal pores were shown to be more than 450% concerning the applied remote stress amplitude. The results are a pretext to a scale bridging numerical solution that accounts for the short crack formation stage based on microstructural damage.
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