Theory of Narrow U-Shaped Notches in Linear Fracture Mechanics

2021 ◽  
pp. 57-72
Author(s):  
Yu.N. Ovcharenko
Keyword(s):  
Fracture Mechanics ◽  
Strain State ◽  
Fracture Initiation ◽  
Deformation Energy ◽  
Asymptotic Formulas ◽  
Stress Strain ◽  
Linear Fracture Mechanics ◽  
Stress Strain State ◽  
Linear Fracture ◽  
Corrosive Effect

On the basis of linear fracture mechanics, a complete set of asymptotic formulas is obtained to describe the stress-strain state at the top of a narrow U-shaped notch. This type of defect can be possessed by a crack that has undergone a corrosive effect of the environment, or there can be a crack-like defect in a welded joint, e.g. lack of penetration, undercut, or a narrow slot in the part. To comparatively assess the risk of cracking at the tops of narrow U-shaped notches, and identify the places and directions of fracture initiation, we reveal the possibility of using such energy criteria as the deformation energy density and The previously indicated criteria were proposed by the author of this work for classical cracks-cuts. The purpose of this work was to study, on the basis of singular solutions of linear fracture mechanics, the stress-strain state in terms and near the tops of extremely narrow U-shaped notches, i.e., blunt cracks, in comparison with classical cracks-cuts

Evaluation of strength of carrying metal structures of trailers

2020 ◽  
Vol 2 (100) ◽  
pp. 58-69
Author(s):  
P. Popovych ◽  
L. Poberezhny ◽  
O. Shevchuk ◽  
I. Murovanyi ◽  
T. Dovbush ◽  
...  
Keyword(s):  
External Load ◽  
Strain State ◽  
Deformation Energy ◽  
Strength Analysis ◽  
Preliminary Assessment ◽  
Stress Strain ◽  
Load Bearing ◽  
Metal Structures ◽  
Stress Strain State ◽  
Increased Risk

Purpose: Development of a computational model of stress-strain state bearing elements of trailer frames for preliminary assessment and identification of areas with increased risk of failure. Design/methodology/approach: The object of the study is the processes of loading the load-bearing metal structures of trailers - fertilizer spreaders. The stress-strain state of the spreader bearing system is investigated for the established three typical cases of external load. To refine the values obtained as a result of modelling, they were determined in SOLIDWORKS. Findings: Computational models of load have been compiled by improving the method of minimum potential deformation energy for its effective correct use in analytical studies of a similar type of metal structures. It is proved that for a flat closed frame structure made of thin-walled profiles, loaded with forces perpendicular to the plane of the frame, the levelling of compression and shear energies, as well as axial and transverse forces and bending moments in the horizontal plane does not significantly affect the calculation results. Research limitations/implications: Horizontal components of the shear forces as well as the normal forces and as a consequence the corresponding potential deformation energy are neglected, which has some effect on the accuracy of the calculations. Practical implications: An effective tool for strength analysis with preliminary assessment and diagnostics of load-bearing metal structures based on the constructed calculation models of stress strain state load-bearing frames of typical geometry with an arbitrarily given distribution of external load. Originality/value: A universal algorithm for recording additive functions of bending and torques, as well as the potential deformation energy of welded frames of trailers.

ANALYSIS OF THE KINETICS AND DIRECTIONALITY OF ELASTOPLASTIC DEFORMATION AND FRACTURE

2019 ◽  
Vol 85 (6) ◽  
pp. 47-52
Author(s):  
N. A. Makhutov ◽  
I. V. Makarenko ◽  
L. V. Makarenko
Keyword(s):  
Numerical Methods ◽  
Fracture Mechanics ◽  
Fracture Surface ◽  
Elastoplastic Deformation ◽  
Strain State ◽  
Stress Strain ◽  
Nonlinear Fracture Mechanics ◽  
Stress Strain State ◽  
Nonlinear Fracture ◽  
Cycle Loading

Safety, survivability, and serviceability of the equipment are governed by the strength characteristics of the separate units and elements which can contain initial or operational defects such as superficial differently oriented semi-elliptical cracks. Numerical methods of calculation provide a large bulk of information about the stress-strain state (SSS) of those elements proceeding from the given algorithms for calculating the corresponding fracture models. Change in the type of the SSS near the crack contour when going from the bulk to the surface depends on the constraint of deformations along their front, i.e., on the 3D character of the SSS. Diagnostics of the form change of the defects (surface differently oriented semi-elliptic low-cycle cracks) is carried out on the basis of experimental results and numerical solutions. The data of the finite element modeling are implemented on the basis of macros of the ANSYS program complex. The regularity of the directionality of developing the elastoplastic fracture under low-cycle loading is studied. The proposed methodology is proved by the parametric equations of the kinetics of forming changes of the cracks under study in the fractographic analysis of the surfaces of their development. The results of testing samples with semi-elliptic cracks under low-cycle loading are used in analysis of the parameters of the morphology of the surfaces of the developed defects. The results of measuring fields of elastoplastic deformation intensity in the crack tip and geometrical characteristics of the fracture surface development are presented. Analysis of the dynamics of the local stress-strain state near the contour of multi-oriented defects in parts and structural units of the equipment showed a good agreement between the experimental parameters of the geometry of developing cracks and characteristics obtained by numerical methods. The presented parametric equations specify the characteristics of nonlinear fracture mechanics thus providing reliable estimation and forecasting of survivability, and safety of serviceability of the critical equipment. The deformation criteria of nonlinear fracture mechanics are used to demonstrate the dependence of fracture development on the 3D character of the stress-strain state indicating to the directionality of the geometric development of the fracture surface form.

КОНСТРУКТИВНО-ТЕХНОЛОГІЧНІ ОСОБЛИВОСТІ ХВОСТО-ВИХ БАЛОК СІТЧАСТОГО ТИПУ З ПОЛІМЕРНИХ КОМПО-ЗИЦІЙНИХ МАТЕРІАЛІВ ВЕРТОЛЬОТІВ ТРАНСПОРТНОЇ КАТЕГОРІЇ

2020 ◽  
pp. 15-30
Author(s):  
А. Г. Гребеников ◽  
И. В. Малков ◽  
В. А. Урбанович ◽  
Н. И. Москаленко ◽  
Д. С. Колодийчик
Keyword(s):  
Finite Element ◽  
Strain State ◽  
Layer Structure ◽  
Metal Structure ◽  
Element Model ◽  
Stress Strain ◽  
Element Analysis ◽  
Mesh Structure ◽  
Stress Strain State ◽  
Mesh Structures

The analysis of the design and technological features of the tail boom (ТB) of a helicopter made of polymer composite materials (PCM) is carried out.Three structural and technological concepts are distinguished - semi-monocoque (reinforced metal structure), monocoque (three-layer structure) and mesh-type structure. The high weight and economic efficiency of mesh structures is shown, which allows them to be used in aerospace engineering. The physicomechanical characteristics of the network structures are estimated and their uniqueness is shown. The use of mesh structures can reduce the weight of the product by a factor of two or more.The stress-strain state (SSS) of the proposed tail boom design is determined. The analysis of methods for calculating the characteristics of the total SSS of conical mesh shells is carried out. The design of the tail boom is presented, the design diagram of the tail boom of the transport category rotorcraft is developed. A finite element model was created using the Siemens NX 7.5 system. The calculation of the stress-strain state (SSS) of the HC of the helicopter was carried out on the basis of the developed structural scheme using the Advanced Simulation module of the Siemens NX 7.5 system. The main zones of probable fatigue failure of tail booms are determined. Finite Element Analysis (FEA) provides a theoretical basis for design decisions.Shown is the effect of the type of technological process selected for the production of the tail boom on the strength of the HB structure. The stability of the characteristics of the PCM tail boom largely depends on the extent to which its design is suitable for the use of mechanized and automated production processes.A method for the manufacture of a helicopter tail boom from PCM by the automated winding method is proposed. A variant of computer modeling of the tail boom of a mesh structure made of PCM is shown.The automated winding technology can be recommended for implementation in the design of the composite tail boom of the Mi-2 and Mi-8 helicopters.

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