International Journal of Fracture最新文献

An energy-based analytical model is proposed here to investigate the mechanical behavior of adhesively bonded simple-lap and stepped-lap joints (SLJ) with carbon fiber-reinforced polymer (CFRP) adherends subjected to tensile loading. In this study, the CFRP uni-directional (UD) adherends of ([0]_{16}) and quasi-isotropic (QI) layup sequence of ([45/-45/0/90]_{2s}) are considered to be joined. The governing differential equations (GDEs) of equilibrium are derived for the adhesively bonded adherends in stepped lap joint configuration following an energy-based approach. Additionally, this model is reduced for GDEs of the simple-lap joint configuration. The finite difference scheme is employed to obtain the numerical solution of the proposed analytical model. The field distributions of strain and displacement over the specimen surfaces are captured in the experimental investigation using the full field technique of 2D digital image correlation (DIC). The analytical model generates the load–displacement curve, validated against experimental and finite element (FE) predictions. Additionally, a sensitivity analysis is conducted to assess the influence of the design parameters of the adhesive joint, including the thickness of the adhesive layer, length of overlap region, and elastic modulus. Finally, the analytical model prediction of the peak load for damage in adhesively bonded joints under shear loading is compared with experimental results. The developed analytical model provides an understanding of the mechanical behavior, including possible failure/critical locations of the adhesive joints from the design perspective.

The fatigue crack growth behavior of a submicron-grained WC–Co hardmetal is investigated by artificially introducing small flaws by means of sharp indentation. Similar fatigue testing is also conducted on notched specimens with long through-thickness cracks for comparison purposes. The use of controlled small indentations flaws is shown to be a valid and successful approach for studying and describing crack growth behavior under cyclic loading for the material under consideration. This statement is based on the similitude found in fatigue mechanics and mechanisms between both crack types. Regarding the former, accounting of the indentation-induced residual stresses is key to rationalize the experimental findings. Concerning the latter, inspection of crack-microstructure interaction as well as fracture surfaces permit to discern similar features and scenarios, at both meso- and micrometric length scales. Results from this research yield an immediate practical implication, as indentation techniques may then be proposed as an alternative testing route for investigating fatigue crack growth behavior of hardmetal grades where sharp indentation is capable to induce well-developed radial crack systems.

Contrary to the second-order Phase field model (PFM) of fracture, fourth-order PFM provides a more precise representation of the crack surface by incorporating higher-order derivatives (curvature) of the phase-field order parameter in the so-called crack density functional. As a result, in a finite element setting, the weak form of the phase-field governing differential equation requires (C^1) continuity in the basis function. (C^0) Sibson interpolants or Natural element interpolants are obtained by the ratio of area traced by the second-order Voronoi cell over the first-order Voronoi cells, which is based on the natural neighbor of a nodal point set. (C^1) Sibson interpolants are obtained by degree elevating the evaluated (C^0) interpolants in the Bernstein-Bezier patch of a cubic simplex. For better computational efficiency while accounting only for the tensile part for driving fracture, a hybrid PFM is adopted. In this work, the numerical implementation of higher-order PFM with (C^1) Sibson interpolants along with some benchmark examples are presented to showcase the performance of this method for simulating fracture in brittle materials.

This work examines the void growth and coalescence in isotropic porous elastoplastic solids with sigmoidal material hardening via finite element three-dimensional unit cell calculations. The investigations are carried out for various combinations of stress triaxiality ratio (({mathcal {T}})) and Lode parameter (({mathcal {L}})) and consider a wide range of sigmoidal hardening behaviors with nominal hardening rates spanning two decades. The effect of ({mathcal {L}}) is considered in the presence and in the absence of imposed shear stress. Our findings reveal that depending on the nature of sigmoidal hardening the cell stress-strain responses may exhibit two distinct transitions with increasing stress triaxiality (({mathcal {T}})). Below a certain lower threshold triaxiality the stress-strain responses are sigmoidal, while above a certain higher triaxiality they exhibit softening immediately following the yield. Between these threshold levels, the responses exhibit an apparent classical rather than sigmoidal strain hardening. The sigmoidal hardening characteristics also influence porosity evolution, which may stagnate before a runaway growth up to final failure. For a given ({mathcal {L}}), an imposed shear stress adversely affects the material ductility at moderate ({mathcal {T}}) whereas at high ({mathcal {T}}) it improves the ductility. Finally, we discuss the role of material hardening and stress state on the residual cell ductility defined as strain to final failure beyond the onset of coalescence.

The present study investigates in the failure of adhesive bondings with structural silicone sealants. Point connectors of two circular metal adherends bonded with DOWSIL™  TSSA are subjected to tensile loading. We formulate and use a constitutive law that captures volumetric softening owing to the formation of cavities. Therein, cavitation is considered a process of elastic instability which is homogenized with a pseudo-elastic approach. Ultimate failure initiating from the free edges is predicted employing the framework of finite fracture mechanics. The concept requires both a strength-of-materials condition and a fracture mechanics condition to be satisfied simultaneously for crack nucleation. For the former, we use a novel multiaxial equivalent strain criterion. For the latter, we employ literature values of the fracture toughness of DOWSIL™  TSSA . The predicted onset of cavitation and ultimate failure loads are in good agreement with our experiments. The proposed model provides initial crack lengths that allow for the derivation of simple engineering models for both initial designs and proof of structural integrity while simultaneously extending the range of usability of the structural silicone compared to standardized approaches.

Hydride precipitation ahead of a crack is examined under conditions of hydrogen chemical equilibrium, constant temperature and elastic-plastic power-law hardening metal behavior. The limiting conditions are approached via the interaction of the operating physical mechanisms of material deformation, hydrogen diffusion and hydride precipitation. Hydrides are characterized by hydride volume fraction and isotropic transformation strain. Analytical relations are presented for hydride volume fraction and stress, as well as for hydride precipitation zone boundary. It is shown that there is an annulus, within the hydride precipitation zone, where stresses, although vary according to ({left(1/rright)}^{1/n+1}) -singularity, deviate significantly from the well-known HRR-field, being smaller, according to the difference of hydrostatic stress before and after hydride precipitation. Hydride precipitation zone increases with crack-tip constraint, given by triaxiality parameter (Q).

This work reports a selective median crack propagation phenomenon in glass, leading to a novel glass cutting process. We found that by scribing a glass sample to the extent of plastic deformation with a deformation depth of 100–400 nm, followed by inducing an initial crack, a subsurface crack with a depth of ~ 10 μm was propagated backward along the centerline of the scribed region with a speed of 1 μm/s order. The crack depth and propagation speed were increased by increasing the scribing load. We conclude that the propagation direction was determined by the effect of the shear stress caused by a scribing tip sliding motion.

The objective of this work is to investigate the three-dimensional nature of stationary mode I notch tip fields in a basal-textured magnesium alloy. To this end, crystal plasticity based finite element analyses are performed pertaining to a four-point bend fracture specimen for two notch orientations. In the first orientation, the notch and line perpendicular to it are taken parallel to transverse and rolling directions, respectively, while in the second, they are chosen along normal and transverse directions. An additional simulation is performed corresponding to an isotropic plastic solid obeying the von Mises yield condition. The macroscopic results from the simulations agree well with an experimental study conducted pertaining to the first orientation. A pronounced thickness variation in stresses is perceived up to a radial distance of about 0.4 times specimen thickness from the tip. The stresses and plastic strains near the tip on the specimen mid-plane are higher for the ND-TD orientation, whereas on the surface they are more for the TD-RD case. In the former, multiple slip systems along with profuse tensile twinning is observed near the tip, whereas prismatic slip is preponderant for the latter. The strong anisotropy of this alloy manifests in terms of plastic zone shape and size, near-tip plastic strain/slip distributions and plane strain constraint ratio.

In the last few decades, the advancements made in material characterisation equipment and physics-based multiscale material modeling have generated vast database in the field of Material Science and Engineering. This has inspired material innovators to attempt predicting mechanical properties of synthesised materials using big-data so as to reduce the cost, time and effort for materials innovation. However, the impact of collinerarity has always been a matter of concern in emperical research, specially in such predictions of mechanical properties. In the present work, we revisit NIMS database for steel and study the effect of multicollinearity on regression based models for predicting fatigue strength for the material. We use an iterative scheme to isolate highly correlated parameters contributing in determination of the fatigue strength of the steel. We then construct a regression model using only the non-correlated parameters to make the model more efficient computationally. Our results show that the regression model built after consideration of multicollinearity of the variables provide better performance in comparison with regression model built without consideration of the same.