•The applicability of two mixed-mode I + III fracture specimen are compared.•The effect of loading type on mixed-mode I + III fracture toughness is assessed.•The fracture parameters of both specimens ...are numerically and experimentally obtained.•The influence of stress triaxiality constraints on mixed-mode I + III fracture toughness is studied.
Towards measuring the mixed-mode I + III fracture toughness independent of geometry and loading type, two test specimens were numerically and experimentally compared. The capabilities of edge-notched disc bend (ENDB) and edge-notched diametrically compressed disc (ENDC) fracture test specimens were compared in producing the full range of mixed-mode I + III. Although the geometry of both specimens was similar, the difference of their loading type (i.e., bending and compression) noticeably affected the mixed-mode I + III fracture parameters. The existence of mixed-mode I + III fracture in the crack front of the ENDC specimen was more stable than the ENDB specimen. However, the variation of mode mixities ratio in the ENDC specimen was more sensitive to the rotation of the crack inclination angle than the ENDB specimen. The map of T-stress as the function of mixed-mode I + III geometry factors plotted for both specimens. There was an optimal crack length in the ENDB specimen by which the full range of mixed-mode I + III fracture toughness can be measured independent of geometry and loading type effects. While for the ENDC specimen, the optimum crack length only existed for pure mode III. The full range of mixed-mode I + III fracture toughness tests were performed using both test specimens. The corresponding fracture loads and fracture initiation angles were also obtained for both ENDB and ENDC specimens made of granite rock. The magnitude of pure mode I fracture toughness measured by the ENDB specimen was greater than the ENDC specimen. Conversely, the pure mode III fracture toughness measured by the ENDC specimen was greater than the ENDB specimen. These discrepancies were also predicted by the computed T-stress map. In addition to the T-stress, Tz, process zone size, and the stress triaxiality constraints, which governed the crack propagation path were other effective parameters on the difference between mixed-mode I + III fracture toughness values measured via both specimens.
Abstract Objective The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear ...resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials. Methods Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method. Results The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear—abrasion (third body) and Wear—attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush. Significance The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.
•A reformulated non-ordinary state-based peridynamic model describing the dynamic failure of ductile materials.•Updating the deformation gradient on the bond level, owning information including both ...the non-local deformation and the bond deviation.•A mixed strain-stress criterion describing the bond breaking and considering the temperature effect on the bond level.•Numerical analysis and discussion for failure mode transitions in the Kalthoff-Winkler impact test under different impact velocities.
A non-local correspondence peridynamic model is reformulated to describe the dynamic failure of ductile materials, under the framework of non-ordinary state-based peridynamics. To eliminate the zero-energy mode as well as to improve the numerical stability, the deformation gradient is updated on the bond level, which owns information including both the non-local deformation and the bond deviation. Peridynamic thermo-viscoplastic constitutive formulations are presented for the failure analyses of ductile materials. Moreover, a mixed strain-stress criterion describing the bond breaking and considering the temperature effect is presented on the bond level, in which the bonds can keep intact in calculations. Several comprehensive cases, including a notched tension test and Kalthoff-Winkler impact tests with different velocities, are investigated to verify the applicability of the proposed model for ductile fracture and impact failure. Numerical results, in terms of failure patterns, cracking switching and propagation, as well as adiabatic shear band propagation, show a reasonable agreement with corresponding experimental observations.
We present a gradient-based theoretical framework for predicting hydrogen assisted fracture in elastic-plastic solids. The novelty of the model lies in the combination of: (i) stress-assisted ...diffusion of solute species, (ii) strain gradient plasticity, and (iii) a hydrogen-sensitive phase field fracture formulation, inspired by first principles calculations. The theoretical model is numerically implemented using a mixed finite element formulation and several boundary value problems are addressed to gain physical insight and showcase model predictions. The results reveal the critical role of plastic strain gradients in rationalising decohesion-based arguments and capturing the transition to brittle fracture observed in hydrogen-rich environments. Large crack tip stresses are predicted, which in turn raise the hydrogen concentration and reduce the fracture energy. The computation of the steady state fracture toughness as a function of the cohesive strength shows that cleavage fracture can be predicted in otherwise ductile metals using sensible values for the material parameters and the hydrogen concentration. In addition, we compute crack growth resistance curves in a wide variety of scenarios and demonstrate that the model can appropriately capture the sensitivity to: the plastic length scales, the fracture length scale, the loading rate and the hydrogen concentration. Model predictions are also compared with fracture experiments on a modern ultra-high strength steel, AerMet100. A promising agreement is observed with experimental measurements of threshold stress intensity factor Kth over a wide range of applied potentials.
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•Stochastic identification of the parameters contained in a cyclic cohesive zone model.•Novel test set-up for CT specimen providing more meaningful experimental information.•Crack ...propagation and deformation curves data used in input for the inverse analysis.•Minimum experimental data required for the model parameters unique identification.
Cyclic cohesive zone models provide a useful tool to describe fatigue driven crack propagation, covering a wide range of engineering applications. For a proper use of these models, particular attention must be devoted to the correct calibration of the parameters contained, considering that some of these can be characterized by a large variability and/or by the absence of a precise physical meaning so that they are not amenable to a direct measurement. This paper proposes a robust inverse analysis procedure, to investigate the identifiability of the model parameters governing the fatigue induced damage evolution, in a recently proposed cyclic cohesive zone model. A novel control for compact test specimens providing more meaningful experimental information is proposed. The identification problem is formulated by considering fatigue crack propagation curve and deformations measurements in a discrete number of points of the specimen surface as input data of the inverse algorithm. The finite element operator, adopted to simulate the experimental tests, has been substituted by a proper calibrated meta model to reduce the computational cost of the forward operator and, thus, to solve the inverse problem in a stochastic context through Monte Carlo like procedures. Representative results, obtained starting from virtual data affected by different levels of noise, are reported to highlight the identifiability of the model parameters on the basis of the experimental data adopted. Indications regarding the minimum number of measurements needed to make the inverse problem well-posed are also provided, supporting possible planning of measurements setups for laboratory investigations.
•A micromorphic peridynamic model is proposed.•A bond damage criterion that involves the effect of microstructure is proposed.•The relation between PD parameters and micromorphic parameters is ...discussed.•The effect of the micromorphic parameters on crack propagation is investigated.
This paper proposes a micromorphic peridynamic model (MPD) based on the micromorphic theory and the bond-based peridynamic model (BBPD). In micromorphic theory, the material particle is assumed to be embedded with a micro-volume that consists of many micro-particles. Such assumption enables the micromorphic theory can describe the deformation of the microstructure. The proposed MPD is an extended version of BBPD, where the bond interaction considers the effect of microstructure and the bond can transmit both the peridynamic pair-wise forces and peridynamic pair-wise moments. Under special cases, the proposed MPD can degenerate into the BBPD. In this study, the proposed MPD is applied to simulate the crack propagation of the concrete plate and investigate the effect of the micromorphic parameters on crack propagation. The concrete has a size effect due to the existence of the microstructure, and its mechanical behaviors, especially the fracture behavior, are highly influenced by the microstructure. The numerical examples firstly compare the proposed MPD and the micromorphic finite element method, and the results show good agreement between these two numerical models. Then, mode I, mode II and mixed-mode crack propagations are simulated and the influences of the micromorphic parameters on the crack paths are investigated. The results indicate that the micromorphic parameters have an impact on the local damage initiation and have a weak influence on the main trajectory of crack.
•A novel adaptive mesh refinement strategy is specially developed for phase-field method for fracture.•The virtual crack insertion technique is proposed to simplify the mesh process.•Phase-field ...method with the combination of the two techniques is demonstrated applicable and efficient on 2-D and 3-D cases.
In this paper a novel adaptive refinement strategy, which features no hanging nodes or hybrid elements generated, is proposed for phase-field model to realize the refinement of 2-D quadrilateral elements. The strategy is implemented and proved the capacity of enhancing efficiency in calculation. Meanwhile, the virtual crack insertion technique is developed to simplify mesh generation process in 2-D and 3-D phase-field based fracture models. The technique is also proved to be robust in simulating the initial crack with trial on benchmark examples. The applicability of phase-field method with novel adaptive refinement strategy and virtual crack insertion technique for fracture is demonstrated by numerical experiments of 2-D models containing single and multiple cracks. The work shows great promise in engineering application. In addition, mode I-II-III fracture can be well simulated with virtual crack insertion technique. Therefore, virtual crack is recommended on fracture simulation of 3-D problems for convenient mesh generation and higher computational efficiency.
A fretting fatigue model based on self-steered cracks Erena, Diego; Vázquez, Jesús; Navarro, Carlos ...
Theoretical and applied fracture mechanics,
February 2022, 2022-02-00, 20220201, Letnik:
117
Journal Article
Recenzirano
Odprti dostop
•Fretting fatigue model based on a critical plane parameter.•Simultaneous prediction of fretting fatigue cracks and total life.•Fatigue life prediction considering crack initiation and propagation ...phases.
In this article a new fretting fatigue life prediction model is presented. The model can be classified as a variable crack initiation length: the crack initiation and crack propagation phases are calculated as a function of the crack initiation length, and among all the feasible crack initiation lengths and orientations, that producing the minimum fatigue life is considered. In this new proposal the crack direction is automatically determined as a function of fatigue parameters in both phases: initiation and propagation. The model is applied to a wide experimental campaign of fretting fatigue tests, and excellent correlation is obtained between experimental and predicted fretting fatigue lives and crack paths.
•Crack propagation gauges were applied in crack propagation speed calculation.•Fractal theory was applied in propagated length correction of dynamic crack.•Microscopic fracture surface of three ...sandstones were analyzed by scanning electron microscope.•The chemical composition of green sandstone under different cyclic wetting and drying was measure by X-ray diffraction (XRD).•A larger specimen was used to calculate rock dynamic fracture toughness.
Under dry-wet cycles, rock mechanical parameters may be degraded with material strength reduced and structure stability weakened. The impact test was conducted with large single cleavage semicircle compression (LSCSC) specimens to investigate the effect of dry-wet cycles on rock crucial parameters including dynamic parameters, fracture toughness, elastic modulus and tensile strength. Crack extending gauges (CEG) were applied to investigate fracture time and crack velocity. The fractal theory was introduced to correct the extended length and the speed of the crack. A RSM-SY5 (T) non-metal ultrasonic detector was employed to measure P-wave and S-wave under different dry-wet cycles. Additionally, the chemical composition and microscopic morphology features of sandstone in different dry-wet cycle numbers were determined by using X-ray diffraction (XRD) and a scanning electron microscope (SEM-TM3000). The dynamic stress intensity factors (DSIFs) were computed by ABAQUS software. The fracture toughness under different dry-wet cycle numbers was confirmed by using numerical-experimental method. The investigation demonstrates that the mode I crack propagation was influenced by the number of dry-wet cycles with the crucial parameters, fracture toughness, material parameters, cracking time and average crack propagation speed affected. The fracture toughness decrease and disperse with the increase of dry-wet cycles. With the increase of dry-wet cycle number, the crack propagation speed increases, and the crack initiation time decreases.
In this paper, fatigue tests using SENT specimens with different thicknesses were carried out to evaluate the effect of plate thickness on the DIC measurements and fatigue crack propagation ...properties. The fatigue crack propagation rate da/dN of the thin specimen was slower than that of the thicker specimens. The crack opening/closure behaviors at the arbitrary crack location were evaluated by the crack opening displacement measured by the DIC. The crack opening load Pop was higher with thinner specimens, especially with shorter crack lengths. da/dN was correlated with effective stress intensity factor range ΔKeff based on the Pop at the fatigue crack tip, but the error increased with thinner plate thicknesses and longer crack lengths. The strain range at the fatigue crack tip measured by DIC showed a good correlation with da/dN, irrespective of the plate thickness and crack length.
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