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The basic aspects of the J - A concept of elastoplastic two-parameter fracture mechanics based on a three-term asymptotic description of the stress field at the crack tip are presented. It is noted that the field of elastoplastic stresses at the crack tip is controlled by two parameters of fracture mechanics, namely, J -integral and parameter A . Parameter A is a measure of the deviation of the stress field from the HRR stress field and can be considered a parameter of elastoplastic constraint at the crack tip under conditions of both small- and large-scale yielding. The results of studying the influence of the exponent of the strain hardening of the material, crack aspect ratio, and the thickness of standard specimens with a crack on the elastoplastic stress intensity factor and parameter A are presented. A two-parameter elastoplastic J - A fracture criterion based on the relationship between J -integral and strain (stress) on the surface of the crack-notch and the principle of linear summation of damage is formulated. To reflect the crack-tip constraint, the parameter A is introduced into the criterion equation as a function of applied failure stresses. The elastoplastic fracture toughness as a function of the crack-tip constraint in the fracture criterion is interpreted as the corrected elastoplastic fracture toughness of a specimen with the corresponding constraint parameters A . The results of studying the normalized corrected fracture toughness as a function of failure stresses, crack aspect ratio, and strain hardening exponent of the material are presented.

The concept of the average stress has been employed to propose the maximum average tangential stress (MATS) criterion for predicting the direction of fracture angle. This criterion states that a crack grows when the maximum average tangential stress in the fracture process zone ahead of the crack tip reaches its critical value and the crack growth direction coincides with the direction of the maximum average tangential stress along a constant radius around the crack tip. The tangential stress is described by the singular and non-singular ( T -stress) terms in the Williams series solution. The predicted directions of fracture angle are consistent with the experimental data for the mixed mode I/II crack growth behavior of Guiting limestone.

Research results of damage and failure of unidirectional laminate packages under tension are presented. A study of the kinetics of damage and failure of the laminate structure is carried out by means of acoustic emission (AE) and synchronous video recording. The conformity between failure proceses occurring on the microscopic, mesoscopic and macroscopic scale levels and the recorded AE events including their energy parameters, shape and spectrum is established. The structural–phenomenological approach implemented by dividing the AE data array into energy clusters allows analyzing the degree of damage and failure of the material employing new criteria parameters, namely the registration activity and the weight content of the location AE events in the clusters of the lower, middle and upper energy levels.

Greenhouse gas concentrations are increasing over the past few decades, creating the need to measure their concentration with high accuracy, including for determining their trends, sources, and sinks. In this regard, various methods of regional and global control are being developed. One of the measuring methods is passive satellite method, but they allow for you to get data mainly during the day and outside the poles of the Earth. Another method is active lidar; they require the consideration of various aspects that are related to the technical characteristics of the lidar and methods for solving inverse problems. This article discusses the possibility of using lidars for sensing carbon dioxide from space (orbit 450 km) and from a height of 10 km and 23 km, which presumably corresponds to the aircrafts and balloons. As a method of solving the inverse problem, the method of fully connected neural networks with three layers and pre-training of first layer is considered, allowing for the application of additional data, including the IPDA (Integrated Path Differential Absorption) signal, the scattered DIAL (Differential Absorption Lidar) signal, temperature, and pressure profiles. These estimates show the possibility of measuring the average concentration from an orbit height of 450 km with an error of 0.16%, a resolution of 60 km, with a 50 mJ laser pulse energy, and 1 m diameter telescope. It is also shown that it is possible to obtain the concentration profile, including the near-surface concentration with an error of 2 ppm.

In this article, a new fracture criterion is formulated for a normal rupture crack, the most common in practice, based on the assumption that the tangential stresses in the prefracture zone are equal to the local strength of the material. In this case, the size of the prefracture area and the local strength are determined taking into account the nonsingular Т хx and Т zz stresses included in the asymptotic stress distribution according to Williams and characterizing the two-dimensional local constraint of deformation along the crack front in three-dimensional bodies. An expression for the effective stress intensity factor is obtained. In addition to the classical stress intensity factor, it includes the ratios of the Т xx and Т zz stresses to the yield strength. This makes it possible to take into account the restriction of deformations in the transverse (due to Т xx stresses) and longitudinal (due to Т zz stresses) directions in the vicinity of the crack front. Verification of the developed software tools and the proposed fracture criterion has been carried out. Examples of the implementation of the developed criterion for assessing crack resistance of a plate stretched in one or two directions with a coaxial transverse crack are given.

In this article, a new fracture criterion for a mixed-type crack (type I + type II) is proposed. It is based on the assumption that the maximum tangential stresses in the prefracture region are equal to the local strength of the material. In this case, the size of the prefracture area and the local strength are determined taking into account nonsingular Т хx and Т zz stresses included in the expansion of the Williams stress function. The use of Т хx and Т zz stresses in the calculations allows one to describe the two-dimensional local constraint of the deformation along the crack front in three-dimensional bodies. In addition to K I and K II , the expression for the effective stress intensity factor (SIF) includes the ratios of the Т хx and Т zz stresses to the yield strength. This makes it possible to take into account the constraint of deformations in the transverse and longitudinal directions of the crack front, respectively. An example of the implementation of the developed criterion in relation to the determination of the fracture load of a tensile-stressed plate with a through inclined crack is given. Dependences of the Т xx and Т zz stresses on the plate thickness are presented for various crack slopes and plate thicknesses. It is shown that an increase in the plate thickness and a decrease in the crack slope lead to a decrease in the fracture load.

The assessment of material toughness is governed by codes based largely on rigorous experimental results. However, the problem of transferability from the laboratory specimen to field-scale structures limits the extent to which these results can be used. The present work is a developmental contribution to a new approach for assessing the toughness of pipeline steels. The procedure concerns the interaction between material fracture curve based on the three-parameter fracture criterion () and the surface longitudinal notch driving force of a pipe under internal pressure. This could be applied as an important engineering parameter for assessing the structural integrity of pipelines during long-term operation.

The correlation dependences between the safety factors of the yield stress and the safety factors of the crack resistance characteristics (fracture viscosity, crack resistance diagram, critical J integral, and crack-tip opening displacement) are provided. It is proposed to calculate the probabilistic safety factors at preset failure probabilities by means of the probabilistic safety factors of the yield stress, taking into account their correlation, as well as the independence of the static mechanical performance variation coefficients from the type of limit state. The results of calculating the probabilistic safety factors applied to fracture viscosity and the crack resistance diagram are provided.

A methodology for evaluating the durability of plate elements of structures taking into account biaxial constraints of deformations along the front of a normal rupture crack (mode I crack) is presented. The absence of the available published data in which the prediction of the crack growth is carried out using T xx and T zz stresses which are nonsingular terms in the Williams expansion for stresses at the crack tip is noted. The calculation of the fatigue crack growth rate is based on the Paris equation in which the range of the effective SIF is used instead of the range of the usual stress intensity factor (SIF). In this case, the expression for the effective SIF includes T xx and T zz stresses in addition to the usual SIF. This approach provides taking into account, for example, the thickness of the plate for predicting the durability, which is impossible when only the SIF and T xx stresses are used. The formula for the effective SIF is derived on the basis of the assumption that tangential stresses in the pre-fracture zone are equal to the local strength of the material. In this case, the size of the pre-fracture zone and the local strength of the material are determined taking into account T xx and T zz stresses. The numerical simulation is based on a proprietary finite element program which allows calculating T xx and T zz stresses at the front of a through crack in a plate subjected to cyclic uniaxial and biaxial tension. It is shown that nonsingular T xx stresses primarily describe the effect of biaxial loading on the survivability, whereas T zz stresses describe the effect of the plate thickness on the survivability. It is shown that, with increasing thickness of the plate, the value of the effective SIF increases owing to the increased constraint along the crack front, thus increasing the crack growth rate and decreasing the survivability. With an increase in the stress ratio R , under the condition of a constant stress range, the maximum effective SIF reaches the critical value equal to the fracture toughness much faster, thus reducing the durability. It is shown that, for uniaxial cyclic tension, the durability predicted by the proposed methodology is higher than that in the classical approach, when the conventional SIF is used in the Paris equation. For biaxial cyclic tension of a plate, an increase in stresses directed parallel to the crack banks leads to an increase in crack front constraints and therefore to a decrease in the durability compared to the classical approach. In other words, the classical theory does not always provide a conservative estimate of the durability, which indicates the expediency of using the developed method for calculating the durability taking into account biaxial constraints of deformations along the crack front.

The results of fatigue tests of two geometrically identical and similar in design models of the lower wing panel of a commercial aircraft were analyzed. The panels differed in the way of installing mounting bolts, which connect the skin and stringers. Cold expansion of holes drilled both in the skin and stringer was performed for the first panel before joining. The second panel included no additional treatment after drilling pilot holes and final reaming. The bolts were mounted with an interference fit varying from 1.3 to 2.1% and from 2.9 to 3.2% for the first and the second panel, respectively. Changes in the interference fit were the consequence of a scatter attributed to the presence of a tolerance zone for the diameters of both bolts and mounting holes. A two-step comparison of both technologies was based on the experimental study of residual stress fields. The first stage, being a subject of the present study, included the analysis of residual stress fields arising after removal of the bolts and separation of the skin from stringers. Hole drilling and gradual crack growth were used to determine the components of residual stresses. The deformation response was measured by electronic speckle pattern interferometry. High quality interferograms, which provided a reliable resolution of the interference fringes of ultimate density over the hole edge or directly along the notch borders, were obtained for both ways of local removal of the material. The first (pointwise) method, based on drilling a probe hole, provided a quantitative determination of the residual stress components, starting from 1.4 mm distance from the assemblage hole edge. The second technique implements the crack compliance method of subsequent lengthening of the notch, starting directly from the mounting hole edge. This approach provided for a quantitative analysis of residual stress fields, related to different bolt mounting technologies, proceeding from the comparison of SIF values. A high level of compressive residual stresses near open holes was characteristic for both types of panels. Both experimental approaches showed the benefits of joints, where bolts are mounted into cold-expanded (reinforced) holes. For this case, the estimation of the relaxation parameters of the principal component of residual stresses in the direction of the external load is presented.