Qin Sun

A MODIFIED DUCTILE FRACTURE MODEL INCORPORATING SYNERGISTIC EFFECTS OF PRESSURE AND LODE ANGLE

A modified ductile fracture model is proposed based on continuum damage mechanics and three-stress-invariant criteria. In the modified model, the effects of hydrostatic pressure and Lode angle are considered and combined in the developed fracture envelope. To predict the fracture behaviors of ductile materials, the model is implemented into the commercial finite element platform ABAQUS/Explicit through a user material subroutine VUMAT. The validity of this model is examined by comparing the numerical results with experimental data of round bar and compact tension tests. It is demonstrated that comparing with other three-stress-invariant models the modified ductile fracture model can predict values compare favorably with experimental data especially in the unloading stage. The model can be adopted to predict the fracture patterns and unloading process of ductile materials and thus to investigate the whole range of the elastic-plastic ductile fracture behaviors of materials.

A review on the research progress of push-out method in testing interfacial properties of SiC fiber-reinforced titanium matrix composites

Experimental analysis of single-fiber push-out for SiC fiber-reinforced titanium matrix composites (TMCs) is complicated by the incorporation of large thermal residual stresses, strong chemical bond of the fiber/matrix interface and matrix plastic deformation. This paper summarizes the development of push-out test and the characteristics of push-out test for TMCs such as crack initiating at the bottom face and theoretical analysis of the test. Moreover, it deeply analyzes the progresses of interfacial shear strength and fracture toughness, and work focus is pointed out in future.

Separation dynamics of large-scale fairing section: a fluid–structure interaction study

The separation dynamics of a large-scale fairing section in ground test is investigated numerically using a fluid–structure interaction method. The commercial finite element software MSC/Dytran is adopted to establish the dynamic fluid–structure coupling model of the fairing. Two coupling surfaces are constructed for the inner and outer surfaces of the fairing section. The coupling equations are solved using the sequenced-coupling method, in which the fluid and structural problems are examined by the finite volume method and the finite element method, respectively. A comparison between fluid–structure interaction and dynamical response analysis is performed under the conditions with and without atmosphere effect. Results shown that the consideration of atmosphere effect will attenuate the vibration frequency and slow down the center of mass velocity. The effect of aerodynamic interference on the displacement response indicates that a maximum of 13.3% relative displacement can be induced, which may cause collision between the lower trailing portion of fairing section and the core vehicle. Therefore, it can be concluded that the fluid–structure interaction analysis is essential for evaluating and validating the reliability of separation mechanisms in ground tests.

The influence of interface reaction zone on interfacial fracture toughness of SiC fiber reinforced titanium matrix composites

Abstract A fiber-reaction zone-matrix three-phase model is developed to evaluate the interfacial fracture toughness of titanium alloys reinforced by SiC monofilaments. Based on fracture mechanics, theoretical equations of GIIc are presented, and the effects of several key factors such as crack length and the interface reaction zone thickness on the critical applied stress necessary for crack growth and interfacial fracture toughness are discussed. Finally, the interfacial fracture toughness of typical composites including Sigma1240/Ti-6Al-4V, SCS-6/Ti-6Al-4V, SCS-6/Timetal 834, SCS-6/Timetal 21s, SCS-6/Ti-24Al-11Nb and SCS-6/Ti-15V-3Cr are predicted by the model. The results show that the model can reliably predict the interfacial fracture toughness of the titanium matrix composites. dA is the incremental increase in crack surface area, and dUex is the work done by the loading system, and dUse is the change in strain energy of the system due to crack advance, dUfr is the work done in frictional sliding at the interface.