PSI - Issue 81

Dhanies Wahyu Ardyrizky et al. / Procedia Structural Integrity 81 (2026) 458–464

462

Fig. 6. Von Mises stress contour of the sandwich panel during the fire exposure cycle.

4.1. Effect of thermo-mechanical loading The results shown in Fig. 7(a) clearly indicate that the displacement increases nonlinearly with increasing temperature. The more pronounced displacement toward the positive y-axis indicates that the load carried by the structure is still relatively small, as the material's thermal expansion has a stronger influence on the model's deformation. With the applied load held constant, the maximum mid-span deflection of the sandwich panel reaches only about 1 mm during heating. Meanwhile, during cooling, the expansion from previous heating leads to a dominant buckling effect. The curve's path during cooling does not follow its heating path, forming a hysteresis loop. This behavior indicates inelastic, irreversible deformation throughout a complete thermal cycle. Such deformation occurs due to material softening, creep, and mismatches in thermal expansion coefficients between the layers of the sandwich structure. As a result, almost all parts of the structure experience permanent deformation even though the temperature returns to its initial condition. Fig. 7(b) shows the relationship between axial force and temperature. During the heating phase, at approximately 400 –500°C, the axial force increases to around 2500 kN due to thermal expansion restraint, which occurs when expansion is restricted by structural constraints, thereby generating internal compressive stresses. During cooling, the axial force decreases along a different path, indicating an asymmetry between the heating and cooling trajectories. This phenomenon signifies a reduction in material stiffness and the relaxation of plastic stresses as the temperature increases. The structural load-carrying capacity is inversely proportional to temperature; however, during cooling, some thermal tensile stresses may reappear due to nonuniform contraction.

(a)

(b)

Fig. 7. Thermo-mechanical responses: (a) displacement-temperature correlation; and (b) axial force-temperature correlation.