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In this paper, the triaxial compression tests with different confining pressures and strain rates are carried out on polycrystalline ice samples at − 6 °C, and under these conditions all the samples behave strain softening, with volumetric contraction followed by dilatancy at the lower confining pressure, and dilatancy at the higher confining pressure. Based on the framework of breakage mechanics and the above test data, a binary medium constitutive model is established to describe the mechanical properties of polycrystalline ice samples. In this model, polycrystalline ice is composed of two parts: the bonded elements and frictional elements. The bonded elements behave the mechanical properties of elastic–brittle, and the frictional elements have the mechanical properties of elastoplasticity. Under the external loads, the bonded elements gradually break up and transform into frictional elements, and both bear the load together. With the homogenization theory, the definitions of breakage ratio and strain concentration factor are given, which describe the evolution of the polycrystalline ice structure and the uneven distribution of strain on the mesoscopic level. Some parameters of the constitutive model are determined from the triaxial compression test results and the others are determined by trial and error. Meanwhile, the evolution law of the parameters varying with confining pressure is given. Finally, the test curves are compared with the predicted curves to verify the rationality of the model.

In this paper, the stress–strain responses of frozen sands and an elastoplastic constitutive model based on the homogenization theory of heterogeneous materials are presented. In the model, frozen soils are conceptualized as binary-medium materials consisting of bonded blocks and weak bands, and their mechanical behavior is described with elastic–brittle and elastoplastic constitutive models, respectively. By introducing two groups of parameters (i.e., the breakage ratio (λv and λs) and strain concentration coefficient (cv and cs) related to the spherical and deviatoric stress components), the proposed model incorporates the breakage process of ice crystals and nonuniform strain distributions between the matrix (bonded elements) and inclusions (frictional elements) of the heterogeneous frozen soil samples. Moreover, an elasticity-based model and a double hardening constitutive model are employed to simulate the mechanical properties of the bonded elements and the characteristics of the frictional elements, respectively. To provide appropriate and quantitative predictions with the binary-medium constitutive model proposed here, triaxial compression tests are performed on the frozen and unfrozen sands to determine the individual parameters at confining pressures of 300–1800 kPa. The model validations demonstrate that the predictions agree well with the available laboratory results.

The paper deals with solution of the numerical simulation problem on the stress and strain concentration tensor components in mesoporous silicon-based structures with adsorbed water frozen under spatial constraints. The constructed model takes into account the presence of a natural layer of silicon dioxide on the surface of the pores in the studied materials, the structure of the inhomogeneous medium (the ratio of the oxide layer thickness to the radius of the filamentous pore, as well as the orientation of the pores in the space of the silicon membrane), and the volume content of the components.

When a crack occurs under an installed waterproofing material and moves due to environmental effects (freeze–thaw, settlement, vibration, dead load, etc.), waterproofing materials without adequate elongation or tensile strength properties may break and tear. To enable the selection of materials with proper response against the strain that occur during crack movement, this study proposes and demonstrates a new evaluation method for determining and comparing strain concentration of waterproofing materials under the effect of concrete crack movement. For the proposed testing method and demonstration, three common types of waterproofing material types were selected for testing, poly-urethane coating (PUC), self-adhesive asphalt sheet (SAS) and composite asphalt sheet (CAS). Respective materials are installed with strain gauges and applied onto a specimen with a separated joint that undergoes concrete crack movement simulation. Each specimen types are subject to repeated movement cycles, whereby strain occurring directly above the moving joint is measured and compared with the strain occurring at the localized sections (comparison ratio which is hereafter referred to as strain concentration ratio). Specimens are tested under four separate movement length conditions, 1.5 mm, 3.0 mm, 4.5 mm and 6.0 mm, and the results are compared accordingly. Experimental results show that materials with strain concentration ratio from highest to lowest are as follows: PUC, SAS and CAS.

The low-yielding-strength (LYS) steel is promising for energy-absorbing devices due to its outstanding plasticity. Although the mechanical properties of LYS steel for quasi-static and ultra-high-rate were studied, the link between them has not been established yet. Here we report both experiments and numerical simulations on the dynamic behavior of a LYS steel (quasi-static yielding stress > 225 MPa, LYS225) under moderate dynamic loadings, which covers the typical range of strain rate in engineering applications. Our results quantify the rate effect of LYS225 under moderate loading speed, and the strain-rate dependent constitutive and damage models are proposed. Moreover, the stress and strain concentration for elliptic-holed LYS225 plate is numerically analyzed based on the proposed constitutive model, which shows significant difference compared to the static solutions. This work could bridge the gap between their quasi-static and ultra-high-rate properties, thereby improve the designing precision of LYS steel-based energy-absorbing structures.

Alloys used for turbine blades have to safely sustain severe thermomechanical loadings during service such as, for example, centrifugal loadings, creep and high temperature gradients. For these applications, cast Ni-based superalloys characterized by a coarse-grained microstructure are widely adopted. This microstructure dictates a strong anisotropic mechanical behaviour and, concurrently, a large scatter in the fatigue properties is observed. In this work, Crystal Plasticity Finite Element (CPFE) simulations and strain measurements performed by means of Digital Image Correlations (DIC) were adopted to study the variability introduced by the coarse-grained microstructure. In particular, the CPFE simulations were calibrated and used to simulate the effect of the grain cluster orientations in proximity to notches, which reproduce the cooling air ducts of the turbine blades. The numerical simulations were experimentally validated by the DIC measurements. This study aims to predict the statistical variability of the strain concentration factors and support component design.

The stress and strain concentration in some component has been a significant topic for structural safety assessment. However, the evaluation of the stress and strain concentration based on the widely existing solutions for linear elastic material under static loading would lead to remarkable errors when the material undergoes the dynamic loading, since the coupling effect induced by the nonlinearity of the stress–strain relationship and the strain-rate strengthening could be of significant influence. Here we analyzed the strain-rate dependent concentration of stress and strain for a visco-plastic plate with an elliptic hole subjected to dynamic loading. The three-dimensional stress and strain are calculated by finite element analyses based on a rate-dependent Johnson–Cook model in which the material constants are set according to a typical visco-plastic standard 45 carbon steel. Our results show that both the plastic stress and strain concentration factors significantly depend on not only the strain but also the strain rate. With the increment of the remote strain rate, the stress concentration monotonically increases, while the strain concentration shows decreasing tendency.

In this paper, a new technology for on-orbit cold forming of space truss rods is proposed. For the cold roll forming process of asymmetric cross sections of thin strips, the effects of roll gap and roll spacing on the forming of asymmetric cross sections of strips were investigated using ABAQUS simulation + experiments. The study shows the following. When forming a strip with a specific asymmetric cross section, the stresses are mainly concentrated in corners 2/4/6, with the largest strain value in corner 2. With increasing forming passes, when the roll gap is 0.3 mm, the maximum equivalent strain values are 0.09, 0.24, 0.64 sequentially. Roll gaps of 0.4 mm and 0.5 mm equivalent strain change amplitude are relatively similar, and their maximum equivalent strain values are approximately 0.07,0.15, 0.44. From the analysis of the stress–strain history of the characteristic nodes in corners 2/4/6, it can be seen that the stress and strain changes in the deformation process mainly occur at the moment of interaction between the upper and lower rollers, where the stress type of node 55786 shows two tensile types and one compressive type, the stress type of nodes 48594 and 15928 shows two compressive and one tensile type, and the strain of the three nodes is in accordance with the characteristics of plane strain. When the roll gap is about 0.4 mm, the forming of the strip is relatively good. With increased roll spacing, the strip in the longitudinal stress peak through the rollers shows a small incremental trend, but the peak stresses are 380 Mpa or so. When the roll spacing is 120 mm, the longitudinal strain fluctuation of the strip is the most serious, followed by the roll spacing at 100 mm, and the minimum at 140 mm. Combined with the fluctuation in strip edges under different roll spacings, manufacturing cost and volume and other factors, a roll spacing of 100 mm is more reasonable. It is experimentally verified that when the roll gap is 0.4 mm and the roll spacing is 100 mm, the strip is successfully prepared in accordance with the cross-section requirements. When the rolling gap is 0.3 mm, due to stress–strain concentration, the strip is prone to edge waves in forming. The top of corner 2 of the flange triangular region is susceptible to intermittent tear defects, and the crack extension mechanism is mainly based on the cleavage fracture + ductile fracture.

PurposeThe purpose of this paper is to investigate the strain concentration factor in a central countersunk hole riveted in rectangular plates under uniaxial tension using finite element and response surface methods.Design/methodology/approachIn this work, ANSYS software was elected to create the finite element model of the present structure, execute the analysis and generate strain concentration factor (,) data. Response surface method was implemented to formulate a second order equation to precisely compute (,) based on the geometric and material parameters of the present problem.FindingsThe computations of this formula are accurate and in a great agreement with finite element analysis (FEA) data. This equation was further used for obtaining optimum hole and plate designs.Originality/valueAn optimum design of the countersunk hole and the plate that minimizes the (,) value was achieved and hence validated with FEA findings.

Stress raisers such as holes are inevitable in structures at which stress concentration occurs and the static as well as fatigue strength of the structures can be significantly weakened. Therefore, to accurately evaluate the stress concentration factor and stress fields at holes is of essential importance for structure design and service life prediction. Although stress and strain concentration and fields at holes in finite thickness plates strongly change with and along the thickness, manuals of stress concentration for engineering design are mainly based on two-dimensional theory and no explicit formula is available even for circular holes in finite thickness plates. Here we obtain for the first time a complete set of explicit formulae for stress and strain concentration factors and the out-of-plane constraint factor at circular as well as elliptical holes in finite thickness plates by integrating comprehensive three-dimensional finite element analyses and available theoretical solutions. The three-dimensional stress distributions ahead of holes can also be predicted by the obtained formulae. With their accuracy and the corresponding applicable range being analyzed and outlined in detail, the formulae can serve as an important fundamental solution for three-dimensional engineering structure design and guideline for developing three-dimensional analytical methods.