Research Of Wood Drying Shrinkage Devolopment Process And Drying Contraction Stress

In wood drying and use process,shrinkage stress of wood came into being the moisture loss causes crack.In order to research and test wood drying contraction stress,develop a wood drying contraction stress test equipment.Study drying contraction stress under the different drying condition;the drying contraction stress's research also needs to be able to monitor moisture loss and the decrease of the size at the same time.The use of temperature and humidity test chamber,mechanical sensor,weight sensor,displacement sensor synchronous test lumber in the drying process,moisture content,shrinkage,wood drying contraction stress testing system was optimized.Study and explore the wood drying contraction stress,shrinkage and moisture content with temperature and relative humidity in drying process,the effect of the main contents are as follows.1.The research tested drying contraction stress of pinus sylvestris under different drying condition.The results showed that:(1)Under the condition of the same thickness,high temperature of specimen time get a balanced stress lower than the low temperature,also drying contraction stress change significantly relatively than low temperature,but high stress equilibrium temperature of specimen were relatively less than low temperature drying shrinkage force of specimen.(2)Under the same conditions of temperature,thin specimen to be significantly greater than in the dry shrinkage force thick specimen,in the dry shrinkage force and drying contraction stress peak time required is less than that of thick specimen.With the error caused by individual differences of the specimens test has a certain influence.2.A measurement system was developed in-house and used to simultaneously and continuously obtain the required measurements during drying,which were then used to determine the moisture content,amount of shrinkage,and contraction stress of the wood specimens.This study aimed to investigate the effect of temperature and humidity on the shrinkage and contraction stress of elm wood during drying.A measurement system that was previously developed in-house was used in this study,and we are currently applying for a national patent for this system.It is composed of various sensors,and was placed inside a laboratory-drying chamber where the temperature and relative humidity can be adjusted as required.These measured values were then used to calculate the moisture content and the contraction stress.3.Systematically investigate the effect of the drying temperature,relative humidity,and specimen thickness on the contraction stress in elm wood.Get the following conclusion:(1)When the shrinkage and moisture content reached stable values,the change in the drying contraction stress also became very small.At higher temperatures,the formation of internal checks would lead to a sharp fall of the contraction stress.(2)In the beginning of the drying process,the contraction stress was negative,which resulted from a thermal expansion of the wood.As the moisture content kept decreasing and the shrinkage kept increasing,the contraction stress gradually increased and eventually reached stable values.(3)The significant factor affecting the contraction stress is temperature.The significant factors affecting the shrinkage are the direction of the shrinkage and the specimen size.The significant factors influencing the moisture content are temperature and humidity,as commonly known and expected.