Dynamic Fragmentation Processes Of Ceramic Cylinders Under Quasi-static And Dynamic Compression

Based on experimental method, the compressive failure process and strength characteristics for brittle ceramic materials are researched under quasi-static and impact compressive loadings, and then the compressive fragmentation phenomenon is observed, and the statistical investigations of fragments are also obtained. Subsequent analysis is carried out to explain the mechanisms of failure and fragmentation of brittle materials under compressive loading. We endeavor to establish a relationship to link the brittle material’s mechanical properties(strength, density, ductility, modulus, etc) and the loading conditions(loading rate, stress components), to its fragmentation properties(fragment size and size distributions).We conduct Quasi-static compression experiments to Al2O3 and Sic ceramic cylindrical specimens(Φ10 mm×20mm and Φ10 mm×10mm) using WAW-2000 servo universal machine controlled by computer. Through the experiments we conclude that the ultimate compressive strengths of the two sizes ceramics exceed 2GPa and the average stress of small size sample is higher than that of large one. What’s more the compression performance of Sic is superior to Al2O3 when their sizes are the same. In the experiment, a high-speed photography is used to record the failure process. By combining the images and CT scan after loading-pausing experiments we found that the failure is dynamic destruction process under Quasi-static loading and during the experiment there isn’t observed crack, then the sample is compressed into many small thin columns in a very short time before it fails and final the cylindrical specimen occurs “explosion” failure. Collecting the fragments of the specimen, we conduct the statistical investigations and find that the diameter of Al2O3 is 400-500μm while the diameter of Sic is 300-400μm and the fragments size of the small sample is smaller.Other quasi-static compression experiments are conducted to explore the fracture process effect of the elastic layers coated to Al2O3 cylindrical specimens(Φ10mm×20mm 、 Φ10 mm×10mm).The experiments show that elastic layers has no effect to compressive strength and failure mechanism. However, when coated elastic layers ceramic samples will scarcely have explosion failure, and the fragment size after its failure is bigger than those without elastic layers.We do experiments using split Hopkinson pressure bar to explore the dynamic behavior of ceramic in different strain rates. In the experiments, the sizes of Sic and Al2O3 are 5 mm×5mm×8mm, and we set the strain rates to 600/s, 900/s and 1200/s.The experimental results show that ceramic materials have obvious strain rate effect, and the average quasi-static compressive strength of Al2O3 is about 1.5GPa and Sic is 2.5GPa.Meanwhile,the compressive strength enhancement effect is obvious as the strain rate increases. Failure of the ceramic at high strain rates results from rapid growth of multiple cracks caused by compression and failure occurs in a very short time. We analysis the diameter of fragments then find that the fragment sizes are different when the specimen are in different batches and different densities. However, the fragments sizes still have rules to follow. The debris size of Al2O3 is bigger than Sic and the fragments size in dynamic compression is smaller than that in static compression when the samples have the same sizes.