微损测试饱水木质文物抗弯强度的新方法

A new non-destructive method for flexural strength testingof waterlogged archaeological wood

力学性能是考古出土饱水木质文物进行保存状况评估的基础信息,亦是保护工作中加固增强的核心任务,但囿于取样量和尺寸,饱水木质文物力学性能表征较为困难,亟需开发适用于饱水木质文物的微损、精确测试力学强度的新技术。本研究提出使用静态热机械分析仪(TMA)作为饱水木质文物抗弯强度测试的新方法,以“南海Ⅰ号”沉船出水的马尾松船板为对象开展适用性研究。对32个尺寸为8 mm×2 mm×0.3 mm的饱水木材试样进行测试,获得置信水平0.95以上的抗弯强度有效数据31个。结果表明,“南海Ⅰ号”沉船出水的木质文物断裂应变集中在0.5%~1.75%,平均抗弯强度仅为5.64 MPa,与健康马尾松30 MPa的抗弯强度相比大幅降低。另外,发现晚材占比高的试样强度普遍高于早材试样。本研究说明,TMA能够有效测出强度极低的脆弱饱水木质文物的力学数据,所需试样尺寸在毫米级别,测试精度高,数据重复性好,是一种微损精确的测试方法,有力填补了现有木质文物力学测试方法在微小尺寸上的空白,对脆弱饱水木质文物具有较好的适用性和较大的应用前景。

Mechanical properties provide essential information for assessment of preservation in waterlogged archaeological wood,as well as for the core task of reinforcement and enhancement in conservation work.However,being limited by the amount and dimensions of samples,the mechanical characterization of waterlogged archaeological wood has long been challenging.Thus,there is an urgent need to develop new technologies for testing mechanical strength of waterlogged archaeological wood in a non-destructive and accurate way.This study proposed,for the first time,the use of a thermomechanical analyzer(TMA)as a new method for testing the flexural strength of waterlogged archaeological wood.Its applicability was investigated with the shipboard(Pinus sp.)of the NanhaiⅠshipwreck as the study object.In this study,32 waterlogged archaeological wood specimens,with the dimension of 8 mm×2 mm×0.3 mm,were taken and tested,and 31 valid flexural strength measurements above the 95%confidence level were obtained.The results show that the fracture strain of waterlogged archaeological wood was concentrated between 0.5%and 1.75%and the average flexural strength was only 5.64 MPa,which was significantly lower than the value of 30 MPa seen for the healthy pine wood.In addition,it was found that the strength of samples with a higher percentage of latewood was generally higher than that of earlywood samples.This study illustrates that the use of the TMA can effectively measure the mechanical properties of fragile and waterlogged archaeological wood of very low strength,and requires millimeter-level samples.TMA measurements boast high testing accuracy and good data repeatability,and provide a new non-destructive and accurate testing method that effectively complements the existing mechanical testing methods for fragile archaeological wood in terms of tiny sizes,and has good applicability and application prospects.