Zhongbin Zhou

Quasi-static tensile deformation and fracture behavior of a highly particle-filled composite using digital image correlation method

Polymer bonded explosives (PBXs) are highly particle-filled composite materials. This paper experimentally studies the tensile deformation and fracture behavior of a PBX simulation by using the semi-circular bending (SCB) test. The deformation and fracture process of a pre-notched SCB sample with a random speckle pattern is recorded by a charge coupled device camera. The displacement and strain fields on the observed surface during the loading process are obtained by using the digital image correlation method. The crack opening displacement is calculated from the displacement fields, the initiation and propagation of the crack are analyzed. In addition, the damage evolution and fracture mechanisms of the SCB sample are analyzed according to the strain fields and the correlation coefficient fields at different loading steps.

Study on dynamic fracture and mechanical properties of a PBX simulant by using dic and SHPB method

The deformation and fracture of a PBX simulant were studied in this work. A pre-cracked semi-circular bending sample was loaded using a SHPB. The failure process of the sample was recorded in situ using a high speed camera. Based on the recorded images corresponding to the loading steps, the displacement and strain fields were determined using digital image correlation method. The crack opening displacement was determined. The correlation coefficient distribution was used to predict the initiation and propagation of the crack initiated from the tip of the pre-crack. In addition, the dynamic fracture toughness of the specimen was measured. The KIC values were approximately 1.39 ± 0.02, 1.51 ± 0.01 and 1.87 ± 0.03 MPa·m1/2 corresponding to strain rates about 382 ± 13, 455 ± 8 and 621 ± 23 s-1, respectively. The fracture toughness results show strong strain rate dependence.

Macro-Micro Mechanical Behavior of a Highly-Particle-Filled Composite Using Digital Image Correlation Method

Particle reinforced composites represent a large group of materials used in a variety of applications, such as concretes and solid rocket propellant. The mechanical behavior of these materials depends on properties of constitutes and any microstructural changes that may occur in the body under loading. Generally, particles are applied to high stress in these composites. Heterogeneity plays an important role in composite fracture. Because the mechanical properties of dispersed phase and matrix differ from each other, any one of the following micro-damage nucleation mechanisms has been observed during the deformation process, including cracking of particles, debonding at the particle-matrix interface and fracture of the matrix. In addition, failure also depends on the volume ratio of particles to matrix. The polymer bonded explosive (PBX) is a highly filled composite material of crystalline high explosives (90%-95% by weight) in polymer binder. This matter is a kind of functionally energetic materials being used increasingly as energetic fillings in both civil and military applications when a very high performance is required. The mechanical properties of PBX subjected to a range of conditions are important criteria to determine a safe working life. The study on the mechanical properties and the failure mechanisms of PBX has drawn much attention in recent years [1-9]. Low strengths and safety concerns bring additional difficulties in preparing samples and conducting mechanical tests of PBX. Therefore, the fracture behavior and the failure mechanisms of PBX are not full understood, some beneficial works are still need to be done to bring some further insights into this issue. There are many techniques to measure the deformation in experimental test. Strain gauge and extensometer are widely used, while the microstructure deformation can not be provided by these techniques. Significantly, the strain gauge measures the deformation at a single point, which only gives information at one point, and the gauge may provide local reinforcement causing error in the displacement measure. Several high resolution and noncontact optical techniques do have the advantages that they can measure the whole displacement and strain field providing deformation information, and it is enough to follow strains until failure. In recent years, many beneficial works have been reported from Cavendish Lab. The quasi-static deformation fields were measured by this technique. The influence of particles microstructure was found to be significant for its fracture behavior

Quasi-static studies of deformation, fracture and mechanical properties of a PBX simulant using digital image correlation method

Summary The macroscopic deformation and fracture behavior of a polymer bonded explosive (PBX) simulation material were studied by using Digital Image Correlation (DIC) method. The Brazilian test, semi-circular bending test, punch loading and uniaxial loading experiments were chosen for the study. The whole displacement and strain fields were obtained by using DIC method at macro-scale. New sights into fracture processes and failure mechanisms of simulant samples under different quasi-static loading conditions have been obtained. Macro studies show that the experimental results are in agreement with the theoretical analysis. The experimental methods combined with DIC technique have broad applicability to deformation and fracture studies of a variety of composites.