Determination of mechanical characteristic parameters and extrusioncrushing characteristics test for lotus seed kernel

Abstract: In this paper, an innovative compression technology is developed to study and analyze the mechanical properties of lotus seed kernel with regard to elastic modulus, compression strength and ultimate load when the whole lotus seed kernel is under the pressure. The objectives of this paper are to study the damage and crushing characteristics of lotus seed kernel under the condition of squeezing the load and reducing the crushing rate in the processing and transportation. Firstly, the universal testing machine is utilized to implement tests of elastic modulus and compression strength for lotus seed kernel samples. A series of the mechanical properties are measured for the lotus seed kernel with varied moisture content (5.52%, 7.78%, 10.29%, 12.47%, and 15.06%) in terms of vertical elastic modulus, horizontal elastic modulus, longitudinal compression strength and transverse compression strength. The corresponding transverse stress-strain curve and longitudinal stress-strain curve are figured out. The measurement results indicate the vertical and horizontal elastic modulus and compression strength of lotus seed kernel decrease with the increase of moisture content. The longitudinal values are higher than transverse values as to samples with same level of moisture content. Therefore, lotus seed kernel belongs to a kind of anisotropic material. It is much easier to cause lotus seed kernel broken when it suffers horizontal compression. When the moisture content is relatively low (5.52%, 7.78%, 10.29%), there is a linear relationship between stress and strain. Lotus seed kernel shows brittleness. If the moisture content is much higher (12.47%, 15.06%), strain becomes larger, which means lotus seed kernel has great toughness. The regression equation is established for the sake of carrying out regression analysis based on test results of elastic modulus and compression strength. It is obtained that the minimum compression strength and minimum elastic modulus of qualified lotus seed kernel with moisture content smaller than 11% are 5.12 and 37.12 MPa respectively. Furthermore, the crack caused by compression is also discussed on the basis of varied moisture contents and different compression methods. It is measured that the ultimate loads under the flat pressure for 5 experimental samples are 103.52, 89.87, 72.21, 59.60 and 51.73 N, respectively. Similarly, the ultimate loads under the side pressure are 88.19, 72.78, 57.80, 45.58 and 39.16 N, respectively. From the measurement data, the moisture content and compression method of lotus seed kernel have great influence on ultimate loads. The ultimate loads increase with the decrease of moisture content, no matter it suffers side pressure or flat pressure. Furthermore, the ultimate load of side pressure is less than that of flat pressure in terms of same level of moisture content. Therefore, side pressure is much easier to make the lotus seed kernel broken. The first crack positions are the load position, parting surface and area around the drilled hole in flat pressure test. As to the side pressure test, the first crack positions are on the both sides of parting surface. Based on the test results of ultimate loads of lotus seed kernels, a regression model of ultimate loads and moisture content is established. It is calculated that the maximum compression load of the qualified lotus seed kernel (moisture content is less than 11%) should be less than 53.60 N. In practical cases, the compression load should be less than this limit value. Lastly, a dynamic model of lotus seed kernel compression is developed with the finite element method. The stress distribution of pressure states of lotus seed kernel is figured out. The analysis results demonstrate the stress at load position, parting surface and area around the drilled hole is larger in flat and side pressure tests. The parting surface is the weak part of lotus seed kernel. It expresses that the simulation results well fit the crack position and direction in the compression test, which identifies the correctness of measurement parameters. The study results provide a reliable evidence for determining process parameters of processing and conveying equipment in the lotus seed kernel production.