and the trapezoidal tenon 18 b 18 a a deformation structure is designed the deformation structures is formed between the trapezoidal tenon 18 b 18 a arranged on the outer side of either the first tenon 11 or the second tenon 13 and corresponding edge of the floorboard a deformation structure comprises a triangular ridge 18 c comprising a sharp edge 18 e as shown in fig3 4 or a rectangular ridge 18 d comprising a sharp edge 18 e as shown in fig5 6 the sharp edge 18 e leans against a beveled line 17 c of the trapezoidal blind mortise 17 b so as to form a line contact an expansion joint is formed between the other two sides of the triangular ridge 18 c or the other three sides of the rectangular ridge 18 d for avoiding contact in the process of assembly the floorboards dovetail tenon and mortise joint are added on two ends that are intersected with the ends provided with the beveled tenon and mortise joint so as to increase the strength in a direction in perpendicularity to a grain as shown in fig7 dovetail mortises 23 are arranged on the upper part and the lower part of each of the front edge and the rear edge of the first floorboard 1 and the second floorboard 2 and each of the dovetail mortises 23 is provided with the dovetail tenon strip 24 the interlock mechanism can be other structures such as a.