PSI - Issue 81

Mykola Polishchuk et al. / Procedia Structural Integrity 81 (2026) 282–286

284

Table 1. Experimental study plan

Specimen cross section, mm

Water exposure time, hours

Humidity W, %

Series

Wood species

Number of specimens

І(P -0)

Pine Pine Pine Pine Pine

5 5 5 5 5

45x45x250 45x45x250 45x45x250 45x45x250 45x45x250

-

12 17 20 25 34

ІІ(P -0.5) ІІІ(P -1) ІV(P -24) V(P-120)

0.5

1

24

120

All series of prisms were subjected to single short-term axial compression along the grain (DSTU EN 380:2008) (Fig. 2). Deformation measurements were performed using clock-type indicators. The loading rate was 1.5 mm/min.

Fig. 2. Testing of the experimental prisms

3. Results and discussion The secant modulus of deformation under axial compression along the grain is determined as the tangent of the slope of the secant line of the stress- strain curve (σ -u c ) to the u c axis: E'=tgα=σ c u c (1) Based on the conducted experimental studies, the secant modulus of deformation was determined at each load step using the obtained stresses and strains according to equation (1). Calculations were performed for each series using averaged values. Mathematical and statistical analysis showed a linear dependence of the secant modulus of deformation E′ on the load level η. Using the experimental results and equation (1), graphs showing changes in the secant modulus of deformation after water exposure were constructed for each series (Fig. 3).

Fig. 3. Changes in the secant modulus of deformation after water exposure