PSI - Issue 37

A. Prokhorov et al. / Procedia Structural Integrity 37 (2022) 540–546 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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first study of this effect was carried out in Lebedev Physical Institute (USSR) in 1962 [Ding, K.; Ye, L.]. This technique allows creating significant residual stress up to depth of several millimeters. Nowadays, a large number of research teams [Peyre P, Fabbro R,et al.] actively study LSP, including the effect of LSP process parameters (focus size, pulse energy, laser power density, surface preparing procedure) on the value and depth of compressive residual stresses. These parameters are important for design of the residual stress distribution. From a mechanical point of view, laser shock peening induces change in the material structure in a short characteristic time. The formed defect structures have an increased level of stored energy and its evolution can lead to anomalous dissipative behavior of the material during cyclic deformation. The non-destructive prediction of fracture of the material is important part of exploitation of constructions. Infrared measurement is one of the most widely used methods in different engineering areas. Many authors apply IR cameras for fracture prediction in metals, composite and biological materials [Iziumova A. Yu. et al]. There are number of models for fracture prediction which are based on dissipative behavior of the material. This work is devoted to investigation of the heat generation during cyclic loading of metals. It is proposed that the material treated by laser shock peening dissipates more energy due to the high plastic residual stress on the surface. In addition, high-energy dissipation can be used for earlier prediction of fracture. 2. Experimental condition The experiments were carried out using servo-hydraulic testing machine manufactured by BISS Bi-00-100. Tests were carried out for two different materials (Armco-Iron and Titanium Grade 2) in the initial and peened states. The chemical composition is presented in table 1. Mechanical properties of materials are shown in table 2.

Table 1. The chemical composition of materials.

Material

Ti

Fe

O

Ni

N

C

Si

S

Mn

Mo

Cr

H

P

Armco-iron

-

Balance -

0.06

-

0.004

0.05

0.005 0.04

0.01

0.038 -

0.005

Titanium Grade 2

Balance 0.3

0.25

0.03

-

-

-

-

-

-

0.015

-

Table 2. Physical and mechanical properties of the materials. Material Density g/cc Elastic limit (MPa)

Ultimate tensile stress (MPa)

Fatigue limit (MPa)

Armco-iron

7,87 4.51

120 338

260 452

125

Titanium Grade 2

203.4

All tests were carried out using IR measurements of surface temperature. The IR camera FLIR SC5000 was used for temperature measurements. All specimens were polished mechanically and matted with a carbon layer to conduct infrared measurements. 2.1. Armco-iron The geometry of Armco-iron specimen is shown in figure 1. It is important to mention that the specimen has a non standard geometry for the fatigue test. There is a flat surface in the middle part of the specimen for LSP preparing and infrared measurements.