Study on uniaxial tensile mechanical properties of sawdust-magnesium oxychloride cement composites based on AE and DIC techniques

Abstract

Sawdust-magnesium oxychloride cement composite (SMOCC) is a novel building material produced via extrusion, using magnesium oxychloride cement as the matrix and sawdust as the reinforcement. The development of SMOCC can enhance energy efficiency, utilize wood waste, and reduce environmental pollution. Accurately evaluating the tensile mechanical properties of SMOCC under different loading rates is crucial for design in engineering practices. However, the influence of loading rates on crack resistance and damage behavior of SMOCC still lacks systematic comparison. Thus, this research conducts uniaxial tensile tests on SMOCC specimens with three loading rates, namely, 0.1, 0.01, and 0.001 mm/s, to investigate their stress–strain relationship and mechanical properties. Acoustic emission (AE) and digital image correlation (DIC) techniques were adopted to analyze the damage evolution during the tensile loading process. Consequently, a statistical damage constitutive model considering the effect of loading rates was established. The results indicated that all SMOCC specimens exhibited brittle failure modes with similar stress–strain behavior. The tensile stress–strain curves of SMOCC can be mainly divided into elastic, elastic–plastic transition, softening, and fracture stages. The mechanical properties of SMOCC under uniaxial tension are significantly rate-sensitive. This is manifested by a clear increase in tensile strength and a concurrent decrease in peak strain with higher loading rates. The analysis of the strain cloud diagrams collected by DIC revealed the local strain concentration phenomena during tensile damage to SMOCC. With the increase of loading rate, the acoustic emission activity has higher energy and amplitude values. RA-AF analysis confirms that tensile cracks dominate during uniaxial tensile testing of SMOCC. In addition, the proposed damage constitutive model considering loading rates can predict the tensile damage process of SMOCC specimens.