基于冲击应力波测试法的阔叶材原木质量评估

Quality evaluation of hardwood log based on impact stress wave testing

阔叶材原木的质量评估可以为行业提供最优的阔叶材资源利用价值,但低成本、便捷、快速地评估阔叶材原木质量一直是严峻的挑战。基于此,提出了一种冲击应力波测试的质量评估方法,利用矩分析和小波变换提取两种声评估参数——时间中心和阻尼比,并详细推导了基于连续小波变换的阻尼比提取过程。应用该方法对阔叶材样本原木进行分等,原木板材锯切结果对比表明,基于时间中心和阻尼比的原木质量预测分等中,高质量组中的实测高等级板材占有率分别为74.2%和74.0%,低等级板材占3.2%和3.3%;而低质量分组中实测高等级板材分别占21.8%和28.5%,低等级板材占11.2%和8.3%。与传统的声速分等相比,高质量分组中高等级板材占有率提高了约26%,而低质量组中高等级板材占有率降低了15%以上。鉴于木材的变异性和阔叶材缺陷的多样性,综合考虑多个参数的分等结果可能是最佳选择。

Quality assessment of hardwood log can provide the best usage value of broad-leaved wood resources for industry, but a low-cost, convenient and fast method to evaluate quality of hardwood log is a serious challenge. Here, a quality evaluation method based on impact stress wave testing was proposed. The moment analysis and wavelet transform were used to extract two acoustic evaluation parameters of time centroid and damping ratio, and derive the extraction process of damping ratio based on the continuous wavelet transform in detail. The proposed method was applied to classify samples of hardwood log. The cutting results of log boards showed that for log quality’s predicted grade results based on time centroid and damping ratio, respectively, in high quality log groups, high-grade boards occupancies are 74.2% and 74.0%, respectively, while low-grade boards occupancies are 3.2% and 3.3%, respectively;however, in low-quality log groups, high-grade boards occupancies are21.8% and28.5%, respectively, while low-grade boards occupancies are 11.2% and 8.3%, respectively;compared with log quality’s predicted grade results according to the traditional acoustic velocity, in high quality log groups, high-grade boards occupancy is increased by about26%, while in low-quality log groups, high-grade boards occupancy is decreased by more than 15%;in view of the variability of wood and the diversity of hardwood defects, comprehensively considering the predicted grade results according to various parameters may be the best choice.