Experimental Study Of Rice Moisture Stress Field Physics Parameter And Crack Mechanism Under Normal Temperature

Rice is the most important food in our country, so the quality of which effect the level ofpeople life. There will be mechanical damage during mature, reap, threshing, drying, storing andmachining, many studies of stress crack during drying have been reported. But under normaltemperature economic benefit lowed due to moisture absorption or desportion, decrease productgrade, bring stress crack and unsuitable storing temperature or humidity control. The reports aboutthose were less, many parameters in some basic equations are not researched former. Main physicalproperty parameters and crack mechanism in humid stress field of rice kernel were researched inthe study. The relationship between moisture transfer rule and mechanical strength, distortion,crack of rice kernel, etc., which is very useful to rice product quality controlling, humid stressdamage decreasing, quality increasing.Rice moisture content can be controlled by use of different consistency salt and acidliquor,the method of preparing different moisture contents rice sample also be studied and adopted.Such as, temperature humidity preservation box used in testing mechanical physical properties ofrice kernel, tensile and bending experiment device which can be used on rice samples. Configureddark box, CCD photography, image-taking system, pre-experiment to forcast mechanical physicalproperty and moisture transfer property, from which we can know that distance of elastic modulusand passion ratio in tensile process test is not big when renitency strength is much larger thanresist-pull strength, tensile test can be replaced by bending test to research tensile property ofrice, because tensile test is hard to do, experiment research methods and feasibility werediscussed, and suitable humid stress field experiment research plan ere made.Stress-strain relation curve, strength limit, elastic modulus and passion ratio physicalparameters were acquired through axial compression and tensile experiment of equal-sectioncylinder samples of four varieties rice kernel, the change tendency of moisture content according toeach parameter is: strength limit, elastic modulus and passion ratio will decrease while moisturecontent increase.Resist-pull strength limit and elastic modulus in bending test were acquired and therelationship between moisture content and bending property parameters were set-up, throughbending test of rice kernel of four varieties.Test results showed that, resistency strength is much larger than resis-pull strength while elastic modulus and possion ratio is nearly the same of the rice kernel of the same kind andmoisture content. The force-endure situation is 'extend inside press outside' or'press inside extendoutside' of the rice kernel while moisture humid stress crack of rice emerged because tensile stressis up to resist-pull strength limit.Humid linear expansion coefficient testing device of rice was manufactured, the coefficient offour varities under different moisture contents were acquired and studied by using of imageanalysis technology, results showed that humid linear expansion coefficient in length is larger thanthat of width. Expansion of rice in length is larger than that of in width under the same moisturecontent, so crack emerging is vertical length first.Moisture absorption and desportion of rice was observed by use of dynamic image analysis.The relationship among moisture content absorption time and dimension and the relationshipbetween moisture expansion coefficient and absorption time were acquired before craze of rice inanytime. Outside moisture content, absorption depth and moisture grads inside can be estimated.Research showed that, crack emerge and stress will up to resist-pull limit when moisture gradsinside about 6～7.5%/mm during absorption of rice kernel. In order to offer reference data to ricestoring, moisture content bound of storing safety was found under different surrounding relativehumidity.Combined the experiment research results of mechanical physical property arid moisturetransfer property, humid stress crack emerging mechanism were discussed under normaltemperature, humidity field, and stress field analyzed theoretically and triangle unit analyzed byfinite element. Ellipsoid finite element entity model set up by use of constants such as elasticmodulus, possion ratio, humid linear expansion coefficient, moisture diffusion coefficient acquiredrice physical parameters in humid stress field. Humid stress-strain field finite element analysis ofrice by use of ANSYS software, while surrounding humidity and original moisture content wereboundary condition and original condition. Results showed the same as theorial analysis,foundhumidity field, humid stress-strain field distribution of rice inside while absorption and desportion,humid stress crack's emerging and develop were forecast that the disposition of tensile stress focusis the middle of the section while absorption, which is to say, stress crack will emerge first in thecenter of the section and develop along the radial induce crack in width. The results is oppositewhile desorption, there will be the biggest stress in boundary of the section and expanse fromboundary to the center. So, new theory, methods and physical parameters needed are supplied to thehumid stress crack mechanism research of rice under normal temperature.Image processing and wavelet analysis technology were used many times in the study, severalexperiment device were researched and produce, which can solve the problem in the test ofmechanical physical property and moisture transfer property parameters humidity field, humidstress field basic theories were studied by use of parse in elastic theory. Moisture expansioncoefficient, limit bound of moisture grads inside during absorption were acquired throughexperiment, these physical parameters relate to humid stress field were not found in former studies.Finite element simulate analysis of humid stress-strain field of rice combined theorially analysis with experiment research. Results is very important to many arts and crafts in each link. Such asmature, reap, threshing, drying, storing and machining of rice products.