Analysis of biaxial proportional low-cycle fatigue crack propagation for hull inclined-crack plate based on accumulative plasticity

Fracture failures of ship plates subjected to in-plane biaxial low-cycle fatigue loading are generally the coupling result of accumulative plasticity and biaxial low-cycle fatigue damage. A biaxial low-cycle fatigue crack growth analysis of hull structure that accounts for the accumulative plasticity effect can be more suitable for the actual evaluation of the overall fracture performance of the hull structure in severe sea conditions. An analytical model of biaxial low-cycle fatigue crack propagation with a control parameter for ∆CTOD is presented for hull inclined-crack plate. A test was conducted for cruciform specimens made of Q235 steel with an inclined crack to validate the presented analysis. The biaxial accumulative plasticity behavior and the effects of biaxiality and stress ratios were investigated. The results of this study reveal a strong dependence of biaxial low-cycle fatigue crack propagation on biaxial accumulated plasticity.

Peculiar aspects of cracking in prestressed reinforced concrete T-beams

In order to study the cracking of prestressed reinforced concrete T-shaped beam structures, the authors planned and carried out a full-scale experiment with five variable factors. The following factors were chosen as variable factors: the relative span of the shear, the ratio of the table overhang width to the thickness of the beam rib, the ratio of the table overhang thickness to the working height of the beam section, the coefficient of transverse reinforcement, the level of prestressing in the working reinforcement. The article describes the cracking process and the destruction of test beams. It was found that the loading level of an opening of inclined cracks is 53% larger than the loading level of a normal crack opening. Mathematical models of bending moments and transverse forces of cracking were built using the “COMPEX” software. Also, the mathematical models of the crack opening width and the projection length of a dangerous inclined crack were obtained. These models are based on the experimental data. Analysing the obtained models, the complex influence of variable factors on the main parameters of crack formation and crack resistance was established. In particular, it was found that the prestress level in the working reinforcement has the greatest effect on the bending moment of cracking. In this case, the value of the shear force of cracking significantly depends on both the prestressing level in the reinforcement and the relative span of the shear. On the basis of the experimental data, the empirical expression is obtained for determining the projection of a dangerous inclined crack for prestressed reinforced concrete T-shaped beams. The resulting equation can be used to calculate a shear reinforcement.

Evaluation of inclined crack in mixed mode I and II

In this work,we tented to study the mixed mode of failure with two angles of inclination, of a treated steel, for that we tried to determine the parameters of failure as the stress intensity factor, tenacity and the critical energy in mixed mode of a rupture and see the criterion of rupture and seeing the effect of the angles evolution applied for all parameters. of in our close there is a fragile and less ductile rupture.

Theoretical Analysis of the Variation of Hydraulic Pressure in Cracks Under Uniaxial Compression of Water-saturated Rock Pillar

In order to analyse the variation of hydraulic pressure in cracks of water-saturated rock pillar under uniaxial compression,taking the water-saturated rock pillar as the research object,in which the cracks are divided into two types: longitudinal crack and inclined crack, and the elastic-brittle plastic model is used to describe the mechanical behavior of rock. Assuming that the long axial direction of the crack is consistent with the axial direction of the rock pillar, the expression of tensile stress in the direction perpendicular to the long axial direction of the crack under axial compression is derived by using Maxwell model and Inglis formula. Simplifying the crack to flat elliptic, clinical hydraulic pressure in the case of tensile shear failure and compressive shear damage of the cracks are deduced, and the distribution of clinical hydraulic pressure in uniaxial compression cracks with different growth pattern is analysed. The results show that with the propagation of cracks, the clinical hydraulic pressure near the tip is approach to zero, and in case of hydraulic fracturing, the extension should exhibit the characteristic of discontinuity.

Mixed Mode I/II Fracture Analysis of Bi-Material Adhesive Bonded Joints Using a Novel Short Beam Specimen

Until now, some test specimens with different shapes and loading mechanisms have been utilized for investigating the cracking behavior of adhesive bounded joints. In this research, using a novel test configuration called adhesive short bend beam specimen containing an inclined crack and loaded by three-point bending, mixed mode I/II fracture parameters of a crack initiated in the adhesive part is studied. Compared to other test methods, the specimen used in this research needs a lesser amount of material and the fracture test can be performed easily. A large number of finite element models of this specimen were analyzed using ABAQUS code to study the effect of adhesive and adherent type, and also the crack length and loading span distance on KI, KII, T-stress and fracture initiation direction under different mode mixities. The results showed that the fracture parameters (and in particular the shear mode component) are sensitive to the type and location of adherent in the bounded joint; however, the shape and size of fracture plastic zone is not affected noticeably by the type of adhesive-adherent materials. It was also shown that the complete mode mixities ranging from pure mode I to pure mode II can be introduced for adhesive bounded joints using the proposed test specimen and therefore the specimen is a good candidate test configuration for investigating the mixed mode I/II fracture behavior of adhesive bounded joints.

DESIGN MODELS OF THE BEARING CAPACITY OF THE SUPPORT SECTIONS OF BASALT-CONCRETE BEAM STRUCTURES

In the past decade, structures with non-metallic composite reinforcement (FRP) find more and more widespread use in construction practice, especially in buildings and structures for special purposes. Due to its high strength, resistance to chemical and physical corrosion, dielectric and diamagnetic properties, low weight and low thermal conductivity, FRP is increasingly replacing steel reinforcement. However, the wider use of concrete structures with FRP is constrained by insufficient knowledge of the features of their work, insufficient regulatory support and little experience in operating these facilities. Practice has shown the promise and economic feasibility of using FRP in road, hydraulic engineering, transport construction, in the construction of bridge spans, treatment facilities, chemical and food industry facilities, and foundations in an aggressive soil environment. At the same time, the prospects for using basalt-plastic reinforcement (BFRP) are primarily due to the low cost of the main raw material, basalt fibers, due to the presence of significant reserves of basalt in the world. The basic principles of calculation of bending structures reinforced with FRP, in all foreign standards, as well as in the domestic Manual, are the same as for elements with steel reinforcement. The design models of the bearing capacity of the bearing sections of concrete beams reinforced with BFRP are considered. The bearing capacity of inclined sections of elements with large and medium shear spans should be determined by an inclined crack using variable coefficients , taking into account the real length of a dangerous inclined crack , a significant reduction in tensile stresses in transverse reinforcement to . The bearing capacity of the support sections with small shear spans must be determined as for short cantilevers along an inclined compressed strip between the concentrated force and the support using a variable coefficient . This approach provides satisfactory convergence between the calculated and experimental values of the bearing capacity of inclined sections (coefficient of variation BFRP.

Analysis of Mixed-Mode I/II/III Fracture Toughness Based on a Three-Point Bending Sandstone Specimen with an Inclined Crack

The crack-propagation form may appear as an arbitrary mixed-mode fracture in an engineering structure due to an irregular internal crack. It is of great significance to research the mixed-mode fracture of materials with cracks. The coupling effect of multiple variables (crack height ratio, horizontal deflection angle and vertical deflection angle) on fracture parameters such as the stress intensity factors and the T-stress are the key points in this paper. A three-point bending specimen with an inclined crack was proposed and used to conduct mixed-mode fracture research. The fracture parameters were obtained by finite element analysis, and the computed results showed that the pure mode I fracture and mixed-mode fractures (mode I/II, mode I/III and mode I/II/III) can be realized by changing the deflection angles of the crack. The pure mode I and the mixed-mode fracture toughness of sandstone were obtained by a series of mixed-mode fracture experiments. The experimental results were analyzed with the generalized maximum tangential strain energy density factor criterion considering T-stress. The results showed that the non-singular term T-stress in the fracture parameters cannot be ignored in any mixed-mode fracture research, and the generalized maximum tangential strain energy density factor criterion considering T-stress can better predict the mixed-mode fracture toughness than other criteria.