Research On Acoustic Emission Characteristic Of Wooden Material

Acoustic　emission　(AE)　refers　to　the　phenomenon　that　strain　energy　emits　and　radiates　outward　in　waves　when　the　material　or　the　structure　is　damaged　or　broken　under　exterior　load,　AE　technology　is　an　experimental　technology　by　using　the　measurement　　instruments　to　detect　the　AE　signals,to　locate　the　AE　source　of　the　material　or　the　structure　and　to　deduce　its　mechanism.　　　On　the　research　of　AE　technology　on　detecting　the　defects　in　wooden　products,　this　dissertation　mainly　focuses　in　the　following　aspects:　　Establishing　a　set　of　AE　laboratory　system　by　use　of　piezoelectric　sensors,　pre-　amplifiers,general　A/D　sampling　card　etc,Testing　the　AE　characteristic　of　particle-board　during　the　three-　point　bending　experiment　by　utilizing　AE　technology.　It　is　found　when　particle-board　is　loaded　to　be　bent,　the　AE　characteristic　curvel　reflects　particle-board　mechanical　performance　well,　AE　counts-displacement　curve　can　shows　the　utmost　elasticity　point　and　the　damage　one,　Hence　it　can　be　introduced　as　a　supplementary　measure　to　test　the　materials'　mechanical　performance.　AE　technology　is　further　utilized　to　test　the　AE　character　of　the　different　density　samples　during　straining.　It　is　found　that　the　AE　characterictic　follow　the　certain　rules　for　different　density　and　cracks,that　is　the　product　of　the　utmost　load　and　the　square　root　of　crack　length　is　a　constant,Using　three　different　ways　to　test　the　sound　velocity　propagation　in　wood　and　wooden　material,　It　is　found　lead　broken　measurement　is　not　fit　for　testing　sound　velocity　.Develop　AE　signal　application　programs　with　virtue　Labview　software　to　test　the　AE　characteristic　parameter　and　to　analyse　the　AE　frequence　characteristic　which　consititutes　a　set　of　virtue　instruments　to　test　and　analyse,　Using　three　sensors　to　monitor　the　linear　　of　signal　source,　and　a　satisfactory　precision　is　acquired　by　improving　the　testing　methods,　Using　Wavelet　analysis　method　to　study,AE　signals　of　the　particle-board　and　to　overcome　the　defect　of　traditional　Fourier　Translate,　Finally　the　AE　signals　is　successfully　obtained　from　the　strong　background　noise.