基于本征应变法的木材水分梯度估算方法的提出

M. Ogawa, Jin Miyazawa
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引用次数: 0

摘要

木材必须干燥,以稳定其形状,加强,并防止腐蚀和变色前使用。由于脱水通常发生在表层,因此内层的含水率高于表层。因此,较高的水分梯度可能会导致物料在干燥后出现意想不到的变形和裂缝。目前,已有一些无损测量水分含量的技术,但在不进行切片的情况下,很难测量厚度方向上的水分梯度。本研究旨在提出一种基于本征应变法的全原木湿坡估算方法,该方法可通过地表释放应变估算三维残余应力分布。在提出的方法中,脱水收缩用特征斑来表示,特征斑是通过对加工过程中应变片释放的应变进行反分析来估计的。当木材加工过程中必须获得由于湿度梯度引起的释放应变时,该方法的过程基本上可以认为是无损的。为了验证该方法的有效性,采用有限元法对含水分梯度的原木进行了数值模拟。在分析中,对测井曲线进行了防止劈裂的劈裂衬套,以测量表面的释放应变。当厚度方向上的水分梯度较陡时,通过释放应变可以较准确地估算出水分梯度。而当湿度梯度坡度相对适中时,估算精度较差。为了提高估计精度,将一个日志按顺序拆分,并通过合并这些顺序历史尝试一个公式。采用序贯方法可以有效地提高估计精度。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Proposal of an estimation method of moisture gradient in lumbers based on the eigen-strain methodology
Lumbers must be dried to stabilize their shape, to strengthen, and to prevent corrosion and discoloration before using. Since dehydration usually occurs from outer surface, moisture content in inner layers becomes higher than that of outside. Therefore, higher moisture gradient which may cause unexpected deformation and cracks in materials can be seen after drying. Today, there are some non-destructive techniques to measure moisture content but it is difficult to measure moisture gradient in the thickness direction without sectioning. This study aims to propose an estimation method of moisture slope for whole log based on the eigen-strain methodology in which three-dimensional residual stress distributions can be evaluated from released strains on surface. In the proposed method, shrinkage by dehydration is expressed by eigen-stains which are estimated by an inverse analysis from released strains by strain gauges in processing. When released strains due to moisture gradient are obtained in lumber processing of necessity, the process of this method can be regarded as nondestructive, essentially. In order to prove the effectiveness of this method, numerical simulations were carried out for a log with moisture gradient by using FEM (Finite Element Method). In this analysis, a split liner for prevent splitting was conducted to a log to measure released strains on surface. Moisture gradient could be estimated accurately from released strains when moisture gradient in the thickness direction was relatively steep. However, estimation accuracy became poorer when slope of moisture gradient was relatively moderate. In order to improve the estimation accuracy, a log was split in sequential processes and a formulation was attempted by consolidation those sequential histories. And, estimation accuracy could be improved successfully by adopting the sequential manner.
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