| Sandwich Plate System (SPS) is composed of two pieces of steel faceplates and one softpolyurethane core. It was a new kind of sandwich plate appeared at recent years and was wildlyused in construction and reparation in shipbuilding and bridges structure for high strength, rapidreparation and better industrialization. The existing of Polyurethane elastomer make SPS hasmany special additional properties, such as weight reduction, resisting impact. dynamic response,enhancement in the random fatigue behavior, significant acoustic performance and heat insulation.A series of studies on mechanical properties on SPS are carried out in this thesis, and somecontents are listed as followings:1. The preparing method and experiments of polyurethane elastomer are studied and timehistory of hardness was also obtained. On this basis, preparing method of SPS with stiffeningribs was elaborated and the relationship among flow velocity, diameter of tube and pilot pressureis discussed. Fundamental mechanical tests are carried out and viscoelastic constitutive relationswere constructed according to the test results.2. A new equivalent bending analysis method of sandwich plate is proposed based onclassical sandwich bending theory, which can be approximately replaced in enough accuracy.This method avoid the disadvantage of establishing differential equations to be solved inclassical bending sandwich theory, and can be easily understood to apply by engineers.Furthermore, equivalent parameters of SPS reinforced by cross wall are calculated and a FEAmethod is also used to obtain equivalent parameters to compare with the theoretical results. Forviscoelasticity of polyurethane core, bending responses of sandwich plate consideringviscoelasticity of Kelvin constitute relation are also analyzed in case of static loading and cyclicloading.3. On the basis of research of traditional stiffened steel plates, through introducing criticalreduction coefficient of critical load, a theoretical analysis method is proposed to calculatecritical loads of SPS with stiffening ribs. At same time, Eigen value analysis by FEM andbuckling tests of stiffening SPS is also carried out to verify the correctness of theoretical analysis.Local buckling of SPS is also discussed here and critical wrinkling load of faceplate iscalculated. 4.3-points bending tests for sandwich beam specimens with polyurethane core are carriedout and a special failure phenomenon was found that the interface crack will propagate afterunload and the process will last a certain time. From DCB and SLB tests, it is found that thepropagating angle of interface crack has same value for same kind core in different DCB andSLB test. According to the observation of test, a new kind of calculation method is deduced toelaborate critical strain energy release rate. At the same time, the analysis method of criticalfailure criteria is also proposed by using of interface bonded strength, and critical crack lengthcan be obtained.5. Fatigue tests for sandwich beam in elastic stage and plastic stage are carried out in lastchapter. The influence of frequency to the fatigue test is analyzed by using of theoretical methodproposed in chapter3, and found that there exist "rest" effect in fatigue test for sandwich beamwith polyurethane core.. a new liner damage model considering "rest" effect is proposed and the"recover" function is also given which can be used to calculate the increase of fatigue life. Lastly,dewell fatigue test is carried out to verify the "recover" phenomena and fatigue damage modelconsiderting dewell effect. |
