PSI - Issue 36

Petro Yasniy et al. / Procedia Structural Integrity 36 (2022) 211–216 Yasniy Petro et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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15.2% ( u s1 = 0.00059); for alder wood, the strength indicators increase by 10.4% ( σ c1 = 7.4 MPa), and the deformability decreases by 65.1% ( u s1 = 0.00043); for ash wood, the stress practically does not change σ c1 = 8.7 MPa, while the relative deformations of the samples decrease by 26.7% ( u s1 =0.00045).

σ c , MPa

0 10 20 30 40 50 60 70

Birch Alder Ash

u c

0

0,1

0,2

0,3

0,4

0,5

Fig. 2. Actual (complete) diagrams of strain ‘ stress σ c – strain u c ’ of composite materials based on different hardwood species and polymer composite ‘silor’ under the surface modification Analyzing the first section of the diagrams of the mechanical state of composite materials of all wood species under the surface modification in general, we conclude that the strength of wood under the surface modification slightly increases by 6.7-10.4%, and the deformability decreases with a large scatter – from 15.2% to 65.1%. Therefore, the experimental values of hardwood composite materials (end of section II, top of the stress-strain diagram) under the surface modification, in particular maximum stresses (temporary strength) and critical deformations have the following characteristics (Fig.2): for birch wood, the strength increases by 16.9% compared to untreated wood and reaches the mark f c,0,d =53. 9 МPа, the deformability of the samples decreases by 24.7% ( u c,0,d,exp =0,00421); the strength of prisms based on surface modified alder increases by 21.7% ( f c,0,d =49.4 МPа), critical strains fall by 16.6% to the mark u c,0,d,exp =0,00386; the maximum ultimate stresses of ash wood increase by 11.6% ( f c,0,d =57.7 МPа), while deformable indicators decrease by 17.1% ( u c,0,d,exp =0.00521). In the second section, the strength parameters of hardwood and softwood based composite materials increase by 11.6 – 21.7% in comparison with solid 60 years old wood prisms with moisture content of 12%. Deformability, due to modification, decreases in the range of 16.6 – 24.7%. In the third section, the ultimate strains of modified hardwood and softwood had the following characteristics: for birch wood u c,u =0,00645 (20.6% less); alder wood u c,u =0,00530 (19.6% less); ash wood u c,u =0,00865 (16.5% less). Thus, the strain indicators in the third section are reduced by 16.5 – 20.6% in comparison with the values of solid 60 year old wood with a moisture content of 12%. The last fourth section is characterized by a sharp increase in relative strains, as well as for samples of solid wood of different moisture and age, on the descending branch of the diagram ‘ stress-strain ’ . The final deformations were recorded at approximately the same stresses as for composite prisms. After that, all samples were unloaded. Hence, the final marks of relative strains of samples of wood-based composite materials, which we were able to record, had the following values: birch wood u c,fin = 0.2886 (27.9% less than untreated); alder wood u c,fin = 0.2482 (11.2% less); ash wood u c,fin = 0.4093 (3.9% less). In general, in this section there is a decrease in the deformability of solid wood in the range of 3.9-27.9%. We conclude that the modification of wood (surface) contributes to the change of the main indicators of the strain diagram of specimems of hardwood-based composite materials and polymer composition ‘ silor ’ in all its sections, in particular, increases strength and reduces deformability. It should be noted that these characteristics vary in different areas. Based on the experiment, the diagrams ‘ E- η ’ (secant modulus – stress level) were obtained (Fig.3), according to which the initial modulus of elasticity and strain modulus of all investigated composite materials under the surface modification were determined.