| Non-crystalline ceramics/transparent materials are key components in the aerospace,civil and military applications.The main objective of these transparent materials in the design of windshield or armor system is to provide structural integrity,visibility,resistance to potential impact（i.e.bullet,hail,bird,stone,debris,and blast）,and vis-à-vis cost-efficient.Towards this end,chemically strengthened glasses have attracted designers across the globe to use them in transparent laminated structures for aircraft and armor systems due to their superior resistance to surface flaws and better mechanical properties.Under impact loading conditions,when the windshield or transparent armor system fails or cracks,the stress state in the material becomes very complex.Therefore,the optimal practicality of the chemically strengthened glass in dynamic impact applications vis-à-vis the comprehensive knowledge of compressive and tensile strength,fracture initiation,damage development,and propagation is mandatory.This thesis presents an experimental study on mechanical strength,damage propagation and fracture process of monolithic annealed and chemically strengthened aluminosilicate（ALS）glass plates to impact loading with applications to their use in aircraft front windshield and transparent armor design.The material support for this research was provided by Jiangsu Tie Mao Glass Company Limited,Nantong,P.R.China.The work in this thesis has four dimensions to critically analyse the dynamic failure and damage in annealed and strengthened ALS glass,（1）dynamic compression,（2）dynamic tensile,and（3）edge-on impact tests on monolithic annealed and strengthened ALS glass.（4）Last but not the least,to determine the Johnson-Holmquist Ceramic（JH-2）material model for simulating the dynamic impact behaviour of ALS glass plates.The main research content and outcomes are briefed below.Static compression tests were first conducted using the universal testing machine followed by dynamic compression tests at an average strain rate of 650 s-1 and 350 s-1 using a modified Split Hopkinson pressure bar（SHPB）for annealed and strengthened glass,respectively.In dynamic compression tests,high-speed photography and flashlights were made synchronous with a loading pulse to spot the damage/crack initiation,propagation,and fracture process in both types of glasses.Static test data concerning the compressive strength revealed that annealed glass（AG）and chemically strengthened glass（CSG）both showed strain-rate sensitivity.Also,in dynamic compression tests compared to static compression tests,it was found that both types of glass are rate sensitive,and compressive strength remarkably increased at high strain-rate loading.The glass fracture process for both AG&CSG is also analyzed through high-speed imagery recorded during dynamic compression tests.The dynamic failure process revealed that in both types of glasses the damage starts because of axial cracks and causes the failure of specimens.The specimen reaches its maximum load-bearing capacity but after damage saturation,it loses its strength and shatters into fine particles.The high-speed images and associated stress-time history is used to explain the failure mechanism.The axial splitting of specimens leads towards the final rupture of the glass into particles.The crack initiation,propagation,and glass debris are also discussed to explicate the failure mechanism of glass specimens.The tensile strength and fracture behavior of annealed and chemically strengthened aluminosilicate glass under static and dynamic loading conditions was explored using Brazilian disc（BD）tests.Owing to high brittleness and very small failure strain of glass,this test method is preferred to indirectly measure the tensile strength by compressive loading of cylindrical specimens diametrically instead of using a direct tensile test.In this study,based on the BD principle,the static tensile strength is measured by using the universal testing machine,and a modified SHPB with a pulse shaper technique is used to measure the dynamic tensile strength of two types of glasses.The synchronous high-speed photography in both static and dynamic tests is used to capture the damage/crack initiation,crack pattern,and failure process of BD specimens.Also,the strain-time history was recorded from gauges directly embedded on BD specimens in both tests.The test results showed that two types of glasses under investigation are the loading rate-sensitive.In the case of chemically strengthened glass（CSG）,the average static tensile strength was increased three times compared to the static tensile strength of annealed glass（AG）,and a substantial increase in tensile strength of chemically strengthened glass（CSG）was also observed at dynamic loading rate.The high-speed images and collected glass debris during BD tests are analyzed and discussed to explain the rate-sensitivity,fracture mode,and tensile failure process of two types of glasses.The high-speed video suggested that the main central crack caused the splitting or failure in AG and in the case of CSG the main central crack along with multiple cracks the splitting or failure occurred.Finally,the scanning electron microscope（SEM）images of collected glass residue of（AG）and（CSG）were also studied to illustrate the brittle fracture surface,crack pattern,and deformation mechanism in two types of glasses.The damage propagation and fracture process of monolithic annealed and chemically strengthened ALS glass plates are characterized using the Edge-on impact（EOI）testing technique.The EOI experiments on two types of ALS glass plates at a medium impact velocity of～180 m/s with spherical and cylinders steel projectiles were completed using a pneumatic gas-gun.The high-speed images in shadowgraph mode during the impact process were recorded at the framing rate of 1,000,000 frames per second（fps）to visualize the fracture and damage front in annealed and strengthened glass plates.The real-time captured shadowgraphs in the case of AG showed that the damage front initially starts to develop from the impact end and then after traveling some distance arrested in few microseconds and measured average front velocity against cylindrical and spherical projectile was 2658.91 m/s and 1710.0 m/s,respectively.The tensile wave reflection in AG impact case against both types of projectiles was observed.In CSG,the damage front shape and propagation against both types of projectiles were quite different than the AG,front traveled in a self-sustained mode due to the release of elastic stored energy with the velocity of 1746.92 m/s and 1690.12 m/s,respectively.The damage evolution curves plotted from captured high-speed images show that damage traveled slower in the case of the spherical projectile which suggests that the shape of the projectile has a great influence on the fracture process of annealed and strengthened glass.Additionally,the damage-free zones and fracture surfaces were studied using a scan electron microscope（SEM）from collected post-test debris to discuss the fracture process.Finally,an attempt is made to estimate the JH-2 material model parameters for annealed and strengthened ALS glass to simulate the impact problems.The brief introduction of the JH-2 model and its strength,damage,and equation of state（EOS）relations is mentioned.Secondly,using the compression and tensile experimental results for annealed and strengthened ALS glass,the possible JH-2 material parameters were estimated.To validate the estimated model,SHPB compressive test on glass specimen was simulated using Ansys-Autodyn.The good agreement between the stress-strain results in the specimen and reflected and transmitted stress in the bars were achieved.Further,the EOI simulations on monolithic ALS glass plates against cylindrical and spherical projectile impact were validated with test results.The simulation results demonstrated that the JH-2 model for ALS glass gives good predictions of glass damage initiation,development,and spall effects to impact loads. |
