Kryterium pękania struktury bi-materiałowej z ostrym karbem usytuowanym na interfejsie

Grzegorz Mieczkowski

doi:10.17531/ein.2019.2.15

Abstract

The fracture process of bi-material structure with the notch was analysed in this work. For fracture prediction, a criterion based on the Theory of Critical Distances was used. Under analysis were elements made of aluminium alloy and polymer combination (with a various structural notch-tip angle), which then were subjected to the three-point bending test. Values of critical loads resulting from the used hypothesis were compared with values obtained from the experiment. Validation of the selected criterion required defining a qualitative and quantitative description of singular stress fields present around the structural notch-tip area. Therefore, such solutions were obtained and methodology of their determining was discussed.

Highlights

Predicting durability of mechanical structures is a complex process that requires many factors to be taken into account
In the case when the fracture process occurs in a plane in which complex state of stresses is present, the use of numerical solutions may result in an erroneous prediction [13]. Most frequently in such situation, on the basis of analytical description of local stress fields, a global fracture criterion is formulated and it is based on an equivalent stress intensity factor [1, 13, 27] or minimum strain-energy density [9]
Using an equation (6), boundary conditions and the adopted generalized stress intensity factors definition (8), an analytical description of the stress fields occurring in the notch tip area can be obtained [18]: σ ik

Summary

Introduction

Predicting durability of mechanical structures is a complex process that requires many factors to be taken into account. Notches can be classified into many different categories, depending on their shapes, location within a structure, material recurrence or material manufacturing technology They all have one common characteristic – they cause a local increase of stress in the structure under load, and influence its durability and strength. Assuming homogeneity and continuity of a medium, of which a structural element has been made, they formulated limit values for a function, the exceeding of which resulted in material damage These hypotheses did not take into account the significant influence of stress and strain field gradients on the strength. A solution for this problem is an adequately formulated strength criterion This criterion should include accurately determined equation with defined material constants, on basis of which it is possible to predict the moment of cracking process initiation. Γ - Shear modulus’ ratio δ - Imaginary part of eigenvalue λ λ - Eigenvalue λr - Real part of eigenvalue λ μ - Shear modulus ν - Poisson’s ratio σφ ,σ r ,τ rφ -Stresses in polar coordinates φ0 - Cracking propagation angle ψ -Mode mixity ratio

Fracture Criterion

Testing specimens and FEM model

Test results and discussion

Summary and conclusions