Research On Correlation Between NDT Results And Static Bending Properties For Larch

As biomass polymer material, wood has great variability. It will not only affect the mechanical properties of wood, but also cause great uncertainty in wood processing and utilization. In order to make the most use of wood resources, pre-tests must be done to achieve the class differentiation. At present, visual grading and non-destructive testing (NDT) are two effective methods.Using NDT and destructive testing to test wood materials and finding the relationship between NDT results and static properties can not only gain a more comprehensive understanding of mechanical properties, but also provide a scientific basis for strength grading, which has a very theoretical and practical value.In this paper, six hundred and ninety-four full-size Chinese larch (Larix gmelin (Rupr.) Rupr.) sawn lumber and two hundred and twenty-one Larix olgensis sawn lumber were studied. Visual grading was firstly conducted according to ASTM D 245,JAS 1152,DIN 4074, then four NDT methods (mechanical stress grading, transverse vibration, longitudinal vibration and stress wave)and two static bending test methods (ASTM D 4761 center-point flat-wise bending, third-point edge-wise bending) were used to determine the dynamic and static modulus of elasticity (MOE). Finally, modulus of rupture (MOR) was measured by bending flat-wise (third-point loading). By analyzing the relationship between NDT results and static bending properties, we got the main conclusions as follows:1,The relevance of visual grades and static properties (E3S,E4S,MOR) were obvious.2,There was a good correlation between center-point flat-wise bending and third-point edge-wise bending, the correlation coefficient between E3S and E4S was 0.8049, the mean value of E4S was 8.13% (1.3GPa) greater than E3S.3,Relationship between dynamic MOE and static MOE showed large variability, R ranged from 0.4989 to 0.7330. E4S and EMSR had the highest correlation coefficient, R was 0.7330.4,Correlation between static MOE and MOR (R range of 0.6552～0.7535) was better than correlation between dynamic MOE and MOR (R range of 0.3087～0.6439), E4S best correlated with MOR, R is 0.7535.5,Strength prediction model created by MSR, transverse vibration, stress wave and longitudinal vibration were different, the correlation coefficients were 0.6439,0.5914,0.5035 and 0.3087. It showed that using MSR to predict MOR was the best, followed by the transverse vibration and stress wave, the longitudinal vibration method was the worst.