Application Research Of Laminated Veneer Lumber Dynamic Online Detection And Quality Classification

In the wood processing industry,veneer laminate(LVL),as a widely used engineering structural material,not only has the natural characteristics of wood,but also has better bending strength and rigidity than wood sawing,and strong weather resistance.The mechanical and physical properties are favored by users in industries such as wood construction,furniture,interior decoration,transportation and transportation.In order to meet the objective needs of various users for LVL products of different quality levels,the accuracy and reliability of LVL online testing and quality grading results are particularly important.On the one hand,according to the modal theory and the free vibration theory,through the experimental modal method and the free transient excitation method,the dynamic testing of the elastic modulus(MOE)quality of the two samples placed on the Italian Yang LVL plate specimen Test and research,and use the LTL board quality online quality evaluation system based on STM32F103VET6 microprocessor and Python platform to carry out quality points and so on.The normal distribution and Weibull distribution are mainly used for the calculation and analysis of the probability of LVL elastic modulus.On the other hand,in order to verify the correctness of the application of the original LLV dynamic online detection and quality grading research results in the field of actual engineering,the A-level(average E value = 12.69GPa)and B after online detection and quality grading LVL plate products of grade(average E value = 11.42GPa)are used in the manufacture of LVL I-beams,and related mechanical properties are tested,and their verification and evaluation are carried out.Its main research conclusions show that:(1)The frequency values of the modal test of the Italian Poplar LVL free board suspension and the modal test of the Italian Poplar LVL free rectangular plate placed on the sponge are consistent with the results of the mode shapes.The first three frequencies correspond to the firstorder torsional frequencies,respectively,The first-order bending frequency and the second-order torsion frequency;using the free transient excitation method,the E and G values of the LVL free rectangular plate placed on the sponge are measured,which are 3.99% and 3.08% higher than the results of the free plate suspension modal test..(2)The paper verifies the feasibility of using the free transient excitation vibration method to measure the E and G values of the Italian Poplar LVL free rectangular plate placed on the sponge.Among them,the E and G values of 10 LVL plates of 2700 mm × 770 mm differ by 3.98% and 5.87% respectively,and the E and G values of 10 pieces of 2440 mm × 760 mm differ by 2.59% and 7.09%.(3)Carry out calculation and analysis of the probability distribution of LVL elastic modulus.Using the free transient excitation method,the E value of 149 LVL plates of the same batch with different sizes and specifications was tested at 9.819GPa-13.629 GPa,and the coefficient of variation was 13.64%.Through the calculation and analysis of its probability distribution,we know that the probability of the LVL elastic modulus calculated by the Weibull distribution and the normal distribution is equal at a given value;it is recommended to use about 90% of the minimum value of the measured E as the position parameter of the Weibull distribution Eu setting value.(4)Use the online automatic calculation and quality grading detection system of LVL board quality based on STM32F103VET6 microprocessor and Python platform to measure the E value of a batch(20 pieces)of LVL whole board.Among the 20 LVLs in this batch,the maximum E value is 13.21GPa(sample 7),the minimum E value is 10.93GPa(sample 6);the maximum G value is 888Mpa(sample 10),and the minimum G value is 740MPa(Sample No.6).And it is divided into A grade(average E value = 12.69GPa)and B grade(average E value = 11.42GPa)for LVL I-beam mechanical property verification test and evaluation.(5)Design and manufacture LVL plates of A and B grades that have undergone dynamic online inspection and quality grading into LVL I-beams of the same specifications,and carry out compressive bearing capacity and shear bearing capacity measurements.The results show that the average compression bearing capacity of I-beams manufactured with A-level and B-level LVL flanges is 92.61 kN / m and 90.66 kN / m,respectively,that is,the average resistance of A-level Ibeams is higher than that of B-level I-beams.The compressive bearing capacity is 2.1% higher;the average shear bearing capacity of I-beams manufactured with A-level and B-level LVL flanges is 11.60 kN and 11.32 kN,respectively,that is,the average compressive strength of A-level I-beams is higher than that of B-level I-beams The bearing capacity is 2.4% higher.The verification test of LVL I-beams shows that the average compressive bearing capacity and average shear bearing capacity of LVL I-beams made of A-level LVL with large E and G values are smaller than E and G values respectively The average compression bearing capacity and average shear bearing capacity of LVL I-beams made by LVL are 2.1% and 2.4% higher.Obviously,it is feasible that this LVL dynamic online detection and quality grading technology method is applied to actual projects.To summarize,this study can accurately and reliably dynamically detect the elastic modulus and shear modulus of LVL products online,and perform real-time elastic modulus mass grading,which can meet the objective needs of LVL products of different quality levels in many fields.In order to improve the technical content and added value level of the optimized design and process of domestic LVL product structure,it has good economic and social benefits.