| The stress concentration phenomenon generally exists in the actual engineering structure,which causes serious damage to the components and greatly reduces the life of materials,thus greatly affecting people's production and life.Transparent materials,as a new material in the new era,are widely used in various fields and become one of the indispensable materials in the development of industrial products.The phenomenon of stress concentration in transparent material s couldn't be ignored.In this paper,the fracture parameters of transparent materials are studied from two parts: experimental method and numerical method.In the first part of this paper,the fracture parameters of transparent polymethyl methacrylate(PMMA)plates were measured by digital gradient sensitivity method(DGS).Digital gradient sensitive method(DIC)is a new optical measurement method which combines the digital image correlation me thod(DIC)with the photoelastic principle to obtain the deformation inform ation of transparent materials.Digital gradient sensing has many advantages,such as non-contact,full-field measurement,low requirement of experimental environment,simple specimens and equipments,adjustable measurement range and resolution,etc.Therefore,digital gradient sensing method is more suitable for field measurement than other optical measurement methods.Since it was proposed in 2012,it has undergone many years of de velopment and improvement,and the application of digital gradient sensitivity method has attracted more and more attention.However,in practical applications,there are still some shortcomings in the accuracy of displacement and strain measurement due to the algorithm itself and the measurement system.For example,during the loading process of the experiment,rigid-body displacement will inevitably occur to the specimen,thus affecting the measurement accuracy of the digital gradient sensing method.In this paper,the digital gradient sensitivity method is used to measure the angular field in the stress concentration area of PMMA plate and the stress intensity factor(SIF)at the tip of fine crack or V-notch.In addition,the influence of rigid body displacement on measurement accuracy is inevitable in the process of measurement by digital gradient sensitivity method.The improved digital gradient sensitivity method is used to measure the fracture parameters of transparent materials with high accuracy.The research work and achievements of the first part of this paper are mainly in two aspects:First,the digital gradient sensing method is used to measure the angular field of PMMA plate in the stress concentration area.1.Through the three-point bending experiment of PMMA plate,the experimental values of the angular field near the stress concentration area of PMMA plate under different concentrated loads are measured by digital gradient sensitivity method,and compared with the analytical values.2.The compensation region method is used to eliminate the inevitably rigid body displacement in the experiment.The results show that the compensation region method can effectively eliminate the influence of rigid body displacement and obtain high-precision experimental values of angular field.Second,the stress intensity factor at the tip of a fine crack or v-notch is measured by digital gradient sensitivity method.1.Digital gradient sensitivity method was used to m easure the experiment values of stress intensity factor of tip at the different lengths and different opening angl es of the crack or the v-notch in PMMA plates,and compared with the analytical values.2.In this paper,a new deflection angle control equat ion is proposed to extract the stress intensity factor(SIF)according to the influence of the inevitably generated rigid body displacement in the experiment,which can effectively eliminate the measurement error caused by the inevitably generated rigid bo dy displacement in the experiment.In the second part of this paper,the singular hybrid element method is used to calculate the stress intensity factors of V-notch tip in PMMA plate with different opening angles and lengths on one side.The singular hybri d element assumes independent stress and displacement fields in the element interior and on the element edge,respectively.The singularity of the hybrid element is realized by enhancing the stress function.In the construction of stress function,besides Airy stress function,the singular stress term of Williams series expansion of V-notch is added for the first time to accurately describe the stress concentration at the crack tip.After obtaining the stress field function by the singular hybrid element me thod,the stress intensity factor at the tip of V-notch is calculated by the linear least square method.In order to verify the results obtained by the singular hybrid element method,this paper compares the calculation results by ABAQUS finite element sof tware and analytical method.The comparison results fully reflect the advantages of the proposed method,which is efficient and accurate. |
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