1.1 本规程提供了两种可选的物理取样程序:十字形取样和随机取样。程序的选择将取决于试验结果的预期用途、可用于取样和试验的资源以及有关物种的机械财产和比重的现有数据的可用性。 1.2 第三个程序，双采样，主要通过引用被包括在内。此过程通过相关性应用十字形或随机样本的结果，以改进或更新属性值。 1.3 单位- 以英寸-磅单位表示的值应视为标准值。括号中给出的值是对SI单位的数学转换，仅供参考，不被视为标准值。 1.4 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《国际标准、指南和建议制定原则决定》中确立的国际公认标准化原则制定的。 =====意义和用途====== 4.1 本规程包括取样程序，以获得小的、透明的木材样品，当按照试验方法进行试验时 第143页 结合全尺寸产品测试，将提供机械财产，用于推导木材、板材、电杆、原木和其他产品的设计财产。 4.2 根据这些方法取样的试样所获得的数据还提供了密度、生长位置、横截面位置、树高和含水量等因素对机械财产的影响信息。 4.3 当需要有关树高对力学财产影响的信息时，十字形抽样具有主要价值；树的年龄或径向位置；增长率；边材向心材的变化；力学财产与比重等因素之间的关系；以及对物种进行一般比较，以便对特定最终用途产品的物种进行评级或选择。十字形抽样不提供均值、百分位数或其他描述性统计的无偏估计，也不提供将统计置信度与描述性统计估计相关联的方法。 4.4 当需要改进或更新机械性能值的现有估算值时，使用双重抽样，该估算值是确定应力分级木材、胶合板、电杆和打桩以及其他木材产品的容许设计应力的基础。该方法包括通过仔细观察油井来预测一种性质- 估计更容易或更便宜测量的相关辅助属性。通过对总体进行代表性抽样，以高精度获得辅助属性的样本估计。使用较小的独立样本或大样本的子样本来建立辅助属性和期望估计的属性之间的关系。在森林取样时，双重取样采用了比重来预测机械财产。双采样方法提供了平均机械性能值的无偏估计和估计百分比值的近似方法。统计置信度可能与均值估计值相关，但与百分比值无关。 4.5 当需要描述性统计和特性分布特征的概率估计作为确定木材和其他应力的容许设计应力的基础时，使用随机抽样- 评级产品。当某一物种的数据不存在或现有的估计因森林特征的变化而被认为不再适用时，该方法适用。随机抽样比双抽样提供了更好的概率估计，如果必须完成抽样和测试以建立双抽样方法的机械性能比重回归，则随机抽样成本更低，速度更快。

1.1 This practice offers two alternative physical sampling procedures: cruciform sampling and random sampling. The choice of procedure will depend upon the intended use for the test results, the resources available for sampling and testing, and the availability of existing data on the mechanical properties and specific gravity of the species of interest. 1.2 A third procedure, double sampling, is included primarily by reference. This procedure applies the results of cruciform or random samples through correlation to improve or update property values. 1.3 Units— The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 This practice covers procedures of sampling for obtaining small, clear wood specimens which, when tested in accordance with Test Methods D143 and, in conjunction with full-size product tests, will provide mechanical properties for use in deriving design properties for lumber, panels, poles, house logs, and other products. 4.2 Data obtained by testing specimens sampled in accordance with these methods also provide information on the influence on mechanical properties of such factors as density, locality of growth, position in cross section, height in the tree, and moisture content. 4.3 Cruciform sampling is of principal value when information is desired on the influence on mechanical properties of height in the tree; of age or radial position in the tree; of rate of growth; the change from sapwood to heartwood; the relationships between mechanical properties and factors such as specific gravity; and making general comparisons between species for purposes of rating or selecting species for specific end-use products. Cruciform sampling does not provide unbiased estimates of mean values, percentile or other descriptive statistics, or a means of associating statistical confidence with estimates of descriptive statistics. 4.4 Double sampling is used when it is desired to improve or update existing estimates of mechanical property values that are the basis for establishing allowable design stresses for stress-graded lumber, plywood, poles and piling, and other wood products. The method involves predicting one property by carefully observing a well-correlated auxiliary property that is presumably easier or cheaper to measure. A sample estimate of the auxiliary property is obtained with a high degree of precision by representatively sampling the population. A smaller independent sample or a subsample of the large sample is used to establish a relationship between the auxiliary property and the property for which an estimate is desired. As applied to sampling a forest, double sampling has employed specific gravity to predict mechanical properties. The double-sampling method provides unbiased estimates of mean mechanical property values and an approximation method for estimating percentile values. Statistical confidence may be associated with the estimates of the means but not the percentile values. 4.5 Random sampling is used when probability estimates of descriptive statistics and property distributional characteristics are desired as the basis for establishing allowable design stresses for lumber and other stress-rated products. It is applicable when data for a species do not exist or when existing estimates are believed no longer applicable because of a changing forest character. Random sampling provides better probability estimates than double sampling and is less expensive and quicker if sampling and testing must be completed to establish mechanical property-specific gravity regressions for the double-sampling method.