Issue 50

A. Salmi et alii, Frattura ed Integrità Strutturale, 50 (2019) 231-241; DOI: 10.3221/IGF-ESIS.50.19 233 This study presents a tool for simulating the crack growth in thermo-mechanically loaded equipment. This tool is based on the crack block concept and aims to minimize the cost of meshing operations, which are prevalent in this type of application. Moreover, this work is based on the creation of a program in Python language using the advantages of the Abaqus calculation codes, chosen for their respective flexibility in terms of mesh size and geometric modeler, in the absence of a versatile tool. The reminder of the article is organized as follows: Section 2 describes the material used to conduct this study. Section 3 discusses the results and, finally, section 4 summarizes the results of this work and draws conclusions. To study the characteristics of long-standing cracks, all tests were performed in ambient air with a frequency of 10 Hz [7] and under sinusoidal loading of constant amplitude 118 MPa [8], with a load ratio R between 0.1 and 0.7. The purpose of these tests is to characterize the behavior of long cracks in the case of 2024 T3 aluminum alloy plates by determining the propagation threshold and the Parisian law coefficients. Initial crack size a init = 5.08mm capable spread to a critical final size a = 7.18 mm. Fig. 1 shows the sample (30 mm*10 mm*2.29mm) exposed to an initial temperature of 20°C. This study focuses on the behavior of an external crack, since the rate of crack propagation is more severe [9]. S TUDY MATERIAL 2024-T3 alloy he 2024 alloy is a copper magnesium aluminum alloy with a high copper content of up to 4% by mass. Generally, impurities such as iron and silicon are always present in the composition. In addition to the precipitation hardening, fine particles of size ≈ 100 nm formed during heat treatment, alloy 2024 also contains intermetallic particles. These particles are much larger than the hardening precipitates; they are formed during processing and have no effect in the curing process. On the other hand, they have an important role in the phenomena of localized corrosion. Baog et al. [10] estimated that the density of intermetallic is in the order of 300,000 particles/cm 2 . The microstructure of these alloys becomes very complex given the difference in composition and the different forms of this intermetallic, which are of two types: • The particles S (Al2CuMg): according to Bechet et al. [11], the particles S represent 60% of the intermetallic particles present in the alloy 2024-T3. They have a rounded shape, with sizes ranging from 1 to 5 µm [12]. •The particles of Al-Cu-Fe (Mn): several authors have worked on the characterization of these particles according to their size and their chemical composition [10, 11, and 13]. Al-Cu-Fe (Mn) particles are generally larger than S-phase particles, with sizes ranging from 10 to 25 µm and irregular shapes. Tab. 1 summarizes the intermetallic particles of this type present in the 2024-T3 alloy. Table 1 : Synthesis of the different intermetallic compounds of the Al-Cu-Fe (Mn) type present in alloy 2024-T3 Elastoplastic behaviour Tab. 2 presents the standard elastic properties of Aluminum 2024 T3 [15]. Modulus of Elasticity (GPa) Poisson coefficient Coefficient of thermal expansion (mm/m*k) Thermal Conductivity (w/m*k) Specific Heat Capacity (j/kg*k) Density (g/cm 3 ) 73 0.33 22.8 120 870 2.77 Table 2: Mechanical properties of 2024-T3 aluminum alloy T Composition Reference Al7CuFe2 [10, 13] Al12 (Fe, Mn) 3Si [14] Al6 (Fe, Cu, Mn) [11, 13, 14] (Al, Cu) 6Mn [11, 13] Al6MnFe2 [11] Al20 (Cu, Fe, Mn) 5Si [10]