【国外标准】 Standard Test Methods for Nondestructive Evaluation of the Stiffness of Wood and Wood-Based Materials Using Transverse Vibration or Stress Wave Propagation

5.1 The dynamic modulus of elasticity provided by these test methods is a fundamental property for the configuration tested.5.1.1 The rapidity and ease of application of these test methods facilitate their use as a substitute for static measurements.5.1.2 Dynamic modulus of elasticity is often used for surveys, for segregation of lumber for test purposes, for quality assessment of engineered wood products, and to provide indication of environmental or processing effect.5.2 The modulus of elasticity, whether measured statically or dynamically, is often a useful predictor variable to suggest or explain property relationships.5.3 Results from these test methods can be related to other measurements of modulus of elasticity, such as static methods (see Annex A1 and Appendix X4).5.4 These methods use calculations that assume specimens are prismatic in cross-section and are uniform in modulus of elasticity and density.5.4.1 As a result of the above assumptions, the obtained values of modulus of elasticity are dependent on how the specimen is stressed (see Commentary).5.4.2 Transverse vibration and longitudinal stress wave modulus of elasticity are correlated but not necessarily equal.5.4.3 These methods provide a means to establish a model to predict one dynamic modulus of elasticity from another dynamic method or a static method (that is, D198, D4761, etc.).5.4.4 The methods can also be used to estimate the Class I or Class II modulus of elasticity from the Class III method, or the Class I from the Class II method.5.5 Testing specified to be undertaken in accordance with this Method shall include any requirements regarding the following for each Class:5.5.1 Grades and species permitted to be combined to form the training and validation test sample.5.5.2 Selection and positioning of manufacturing or growth characteristics to be included or permitted in the test sample.5.5.3 Moisture content conditioning undertaken prior to testing.5.5.4 Acceptable moisture content adjustment models.5.5.5 Any other sampling and data adjustment requirements to obtain a representative sample of the population under consideration.NOTE 5: Guidance or requirements from applicable product standards or specifications for representative sampling should be considered. See Annex A2.NOTE 6: See Commentary Appendix X4 for additional information (for example, blocking parameter and blocking limits) that may need to be provided for generating a test sample suitable for developing the test method conversion model.1.1 These test methods cover the non-destructive determination of the following dynamic properties of wood and wood-based materials from measuring the fundamental frequency of vibration:1.1.1 Flexural (see Refs (1-3))2 stiffness and apparent modulus of elasticity (Etv) properties using simply or freely supported beam transverse vibration in the vertical direction, and1.1.2 Axial stiffness and apparent longitudinal modulus of elasticity (Esw) using stress wave propagation time in the longitudinal direction.1.2 The test methods can be used for a broad range of wood-based materials and products ranging from logs, timbers, lumber, and engineered wood products.1.2.1 The two flexural methods can be applied to flexural products such as glulam beams and I-joists.1.2.2 The longitudinal stress wave methods are limited to solid wood and homogeneous grade glulam (for example, columns but not products with distinct subcomponents such as wood I-joists).1.3 The standard recognizes three implementation classes for each of these test methods.1.3.1 Class I—Defines the fundamental method to achieve the highest degree of repeatability and reproducibility that can be achieved under laboratory conditions.NOTE 1: Testing should follow Class I methods to develop training and validation data sets for method conversion models (see Annex A2).1.3.2 Class II—Method with permitted modifications to the Class I method that can be used to address practical issues found in the field, and where practical deviations from the Class I protocol are known and their effects can be accounted.NOTE 2: Practical deviations include, for example, environmental and test boundary conditions. Class II methods allow for corrections to test results to account for quantifiable effect such as machine frame deflections.1.3.3 Class III—Method permitting the broadest range of application, with permitted modifications to suit a wider range of practical needs with an emphasis on repeatability.NOTE 3: Online testing machines implemented to grade/sort lumber may be treated as Class III.1.4 The standard provides guidance for developing a model for estimating a non-destructive test method result (for example, static modulus of elasticity obtained in accordance with Test Methods D198) from another non-destructive test method result (for example, dynamic longitudinal modulus of elasticity from measurement of longitudinal stress wave propagation time).1.4.1 The standard covers only models developed from test data obtained directly from non-destructively testing a representative sample using one test method, and retesting the same sample following a second test method.1.4.2 Results used for model development shall not be estimated from a model.1.5 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.1.6 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.1.7 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.