Evaluation Of Mechanical Properties Of Full-size Wood Composite Panels Supported On Four Nodes Using Vibration Methods

Full-size wood composite panels(WCPs)refer to the panels with a nominal size(length ×width)of 2440mm × 1220mm that are the most common in production and sales in the world.This kind of panels are widely used in furniture manufacturing,building construction,packaging,transportation and other industrial sectors.Mechanical property is an important representation for the quality of WCPs.There are different requirements on mechanical properties of WCPs under different service conditions.Modulus of elasticity(MOE),shear modulus and dynamic viscoelasticity are three key indexes for evaluating the mechanical performance of WCPs.At the same time,MOE and shear modulus can also be used to predict the modulus of rupture and internal bond strength of WCPs.Therefore,mechanical properties of full-size WCPs can be evaluated by accurate determination of these indicators.According to the method typically involved in mechanical properties testing of full-size WCPs,several WCPs specimens with a standard dimension need to be cut from different parts of a large-size panel.The small specimens are then destructively tested in a testing machine to obtain mechanical performance index.With the measurement results of several standard specimens,the overall mechanical properties of full-size panels can be derived.This evaluation procedure is destructive in nature,time-consuming,only suitable for product sampling and not suitable for non-destructive and in-line rapid detection.Thus it is significantly necessary to develop a technique of rapid,nondestructive testing and evaluation on direct testing mechanical properties of' the whole full-size WCPs,especially for the WCPs used in building construction industry.In order to assess mechanical properties of full-size WCPs rapidly and nondestructively,this paper presents a new four-node support condition.The four-node support refers to a full-size WCP being supported on four node points,the intersections of two nodal lines of its length and width.These four nodal lines are located at 22.4%and 77.6%of its length and width,respectively.The innovation of this thesis is to determine rapidly and nondestructively three elastic constants(MOE in the length and width direction as well as the in-plane shear modulus)and dynamic viscoelasticity(storage modulus and loss modulus)in the length direction of full-size WCPs using a free vibration method based on four-node support.First of all,based on transverse vibration of thin plate,the calculation formulas were derived between MOE in the length and width direction as well as the in-plane shear modulus of full-size WCPs supported on four nodes and characteristic parameters(corresponding natural frequencies of the most sensitive modes,the panel density and geometry size)using sensitivity analysis and Rayleigh method.This was theoretical basis for determination of elastic constants of the full-size WCP supported on four nodes using a free vibration method.Secondly,the first nine modal parameters(natural frequency and mode shape)of the vibration of full-size WCPs under the completely free boundary condition and supported on four nodes were tested by experimental modal analysis,respectively.The first nine modal parameters of full-size WCPs supported on four nodes were also studied through theoretical modal analysis.Thirdly,the software for determining elastic constants of full-size WCPs supported on four nodes using a free vibration method was developed using Lab VIEW software.Fourthly,to examine the validity of the vibration testing method,the dynamic and static tests for determining elastic constants of full-size WCPs were conducted,and the test results were compared and analyzed.Finally,theoretical basis for determination of dynamic viscoelasticity in the length direction of the full-size WCP supported on four nodes using a free vibration method was proposed,and the feasibility of the method was verified by tests.The result of this study shows that simultaneous nondestructive determination of MOE in the length and width direction as well as the in-plane shear modulus of full-size WCPs supported on four nodes based on transverse vibration of thin plate theory using a free vibration method is feasible;the first nine modal parameters of full-size WCPs supported on four nodes can be analyzed through both experimental and theoretical modal analysis;the testing software developed works quite well with a user-friendly interface,which provides software foundation for commercial development of laboratory testing equipment for measuring nondestructively mechanical performance of large-size WCPs;this vibration test method is a valid approach for determining the dynamic viscoelasticity in the length direction of full-size WCPs.