PSI - Issue 28

Giacomo Risitano et al. / Procedia Structural Integrity 28 (2020) 1449–1457 G. Risitano et al./ Structural Integrity Procedia 00 (2019) 000–000

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locally weighted scatter plot smooth filter ( rlowess ), with a data span of 10%, was adopted to clean the temperature signal from outliers and to enhance the thermoelastic trend. This kind of filter uses locally linear regression to smooth data defining a span in which each data point assumes a weight depending on its distance from the data to be smoothed. 3.2. Numerical simulation A nonlinear finite element model was implemented on Ansys® APDL, adopting 1/8 th of the specimen geometry (Fig. 3). The elasto-plastic material behavior of C45 steel was modelled adopting a multilinear isotropic hardening plasticity model with true stress-strain data from (Colombo and Vergani, 2019). The material properties of C45 are reported in Table 1. Hexahedral 20-node SOLID186 elements were chosen and, after a calibration procedure, a number of 3584 elements were adopted. Symmetric boundary conditions were applied to the geometry, while the tensile force was equally distributed on the grip section nodes.

Fig. 3. Finite element model

Table 1. C45 mechanical and thermal properties

Density

Specific heat

Tensile Stress at Yield

Tensile Modulus E [GPa]

Poisson’s ratio

Linear expansion coefficient

Thermoelastic coefficient

σ y [MPa]

ν

ρ [kg/m

3 ]

c [J/kg.K]

α [K -1 ]

K

m [Pa

-1 ]

3.17x10 -12

435

210

0.33

7860

480

12 x 10 -6

4. Results and discussions A series of static tests has been conducted on three specimens. The stress rate was chosen properly in order to assure adiabatic test conditions. As an example, in Fig. 4 the applied nominal stress is reported versus the specimen’s surface temperature variation, estimated as the difference between the instantaneous temperature and the initial temperature of the surface recorded at time zero (ΔT = T i – T 0 ). The temperature data has been filtered with a rlowess filter in order to reduce the outliers and highlight the thermoelastic trend.