STUDIES ON THE DYNAMIC FRACTURE PROPERTIES AND FAILURE MODES OF A PBX

2014 ◽  
Vol 06 (04) ◽  
pp. 1450039 ◽  
Author(s):  
R. CHEN ◽  
L. CHENG ◽  
Y. LIN ◽  
F. LU
Keyword(s):  
Dynamic Fracture ◽  
High Speed ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Particulate Composite ◽  
Image Correlation ◽  
Initiation Toughness ◽  
Hopkinson Pressure Bar ◽  
Fracture Properties ◽  
Fracture Velocity

Polymer-bonded explosives (PBXs) are particulate composite materials composed of crystalline explosive grains bound in a relatively soft polymeric binder. It is important to optimize the fracture properties, while still maintaining the low sensitiveness and high explosiveness of PBX. This paper describes a study on the fracture properties and failure modes of a PBX by adopting a newly proposed dynamic fracture experimentation method — notched semi-circular bend (NSCB) specimen loaded with split Hopkinson pressure bar (SHPB) which was used in this study. This method offers the advantage of simultaneously determining the fracture initiation toughness, fracture energy, fracture propagation toughness and fracture velocity. The crack propagation is monitored by using a synchronous high-speed camera, which allows the observation of strain field history via digital image correlation process. The experimental results indicate that both the initiation toughness and the propagation toughness linearly increase with loading rate. The propagation fracture toughness is found to increase with fracture velocity, and a limiting fracture velocity is obtained. The failure modes are interpreted by using various theoretical models. Results suggest that the debonding strength of the binder is much smaller than the crystal fracture strength. The tensile strength is similar to the debonding strength, while the compression strength is somewhere intermediate between them.

scholarly journals Experimental Study on the Temporal and Morphological Characteristics of Dynamic Tensile Fractures in Igneous Rocks

2021 ◽  
Vol 11 (23) ◽  
pp. 11230
Author(s):  
Xuan Xu ◽  
Li-Yuan Chi ◽  
Jun Yang ◽  
Qi Yu
Keyword(s):  
Dynamic Fracture ◽  
Incubation Time ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Gaussian Function ◽  
Morphological Characteristics ◽  
Igneous Rocks ◽  
Frame Rate ◽  
Image Correlation ◽  
Tensile Fractures

In order to investigate the temporal and morphological characteristics of dynamic tensile fractures, experiments on Brazilian specimens machined from igneous rocks (Breccia and Andesite) are carried out with the split Hopkinson pressure bar (SHPB). Detailed observation of the fracture processes of the Brazilian specimens is captured by high-speed camera at a frame rate of 100,000 frames per second. The rate-dependent effect of the dynamic tensile strength of the two igneous rocks is fitted and predicted by the incubation time criterion. Digital image correlation (DIC) is used to calculate the full-field tensile strain distributions on the specimen surface during the loading stage preceding fracture, and this hysteresis of dynamic fracture relative to stress level is interpreted by introducing the concept of incubation time. After the main crack appears, image processing technology is exploited to extract the pixel information of cracks in the high-speed images. Then, FracPaQ quantifies the morphology of the fragmentized process by filling the binarization of cracks with fracture traces. After coordination of the statistical information from these fracture traces, the rose diagram representing their angles and length weights can visually represent the fragmentized characteristics of the Brazilian specimen. Specifically, length-angle distributions of fracture traces at various moments are consistent with the Gaussian function, and the curve fitting parameters reflect differences in the fracture behaviors between the two igneous rocks. In conclusion, the dynamic fracture characteristics of two igneous rocks in dynamic splitting processes are quantified statistically, which can provide references for relevant research.

scholarly journals Rock Dynamic Fracture Characteristics Based on NSCB Impact Method

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Yanbing Wang
Keyword(s):  
Fracture Toughness ◽  
Dynamic Fracture ◽  
High Speed ◽  
Loading Rate ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Fracture Toughness ◽  
High Speed Photography ◽  
Rate Dependency ◽  
Hopkinson Pressure Bar ◽  
Rock Materials

In 2012, the International Society for Rock Mechanics (ISRM) recommended a new Notched Semicircular Bend (NSCB) method for the determination of dynamic fracture toughness of rock materials, but it did not consider the effect of some uncontrollable factors in the course of the experiment on the test result. This thesis firstly carried out dynamic fracture toughness experiments on several typical rock materials such as sandstone using the modified Split-Hopkinson Pressure Bar (SHPB) experimental system with high-speed photography, directly compared the dynamic fracture failure characteristics of several rock materials, and examined the loading rate dependency of the dynamic fracture toughness of rock materials. Based on the numerical analysis method of Discrete Lattice Spring Model (DLSM), it focused on the effect of bullet impact loading rate, loading area of incident bar, support restraints of clamping specimen, and other uncontrollable factors in the course of SHPB experiment on test results. The findings can be referenced for the improvement of NSCB method.

scholarly journals Experimental Investigation of the Dynamic Tensile Properties of Naturally Saturated Rocks Using the Coupled Static–Dynamic Flattened Brazilian Disc Method

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4784
Author(s):  
Xinying Liu ◽  
Feng Dai ◽  
Yi Liu ◽  
Pengda Pei ◽  
Zelin Yan
Keyword(s):  
Tensile Properties ◽  
High Speed ◽  
Loading Rate ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Strength ◽  
Image Correlation ◽  
Dynamic Loads ◽  
Hopkinson Pressure Bar ◽  
Dynamic Tensile Strength ◽  
Brazilian Disc

In a naturally saturated state, rocks are likely to be in a stress field simultaneously containing static and dynamic loads. Since rocks are more vulnerable to tensile loads, it is significant to characterize the tensile properties of naturally saturated rocks under coupled static–dynamic loads. In this study, dynamic flattened Brazilian disc (FBD) tensile tests were conducted on naturally saturated sandstone under static pre-tension using a modified split-Hopkinson pressure bar (SHPB) device. Combining high-speed photographs with digital image correlation (DIC) technology, we can observe the variation of strain applied to specimens’ surfaces, including the central crack initiation. The experimental results indicate that the dynamic tensile strength of naturally saturated specimens increases with an increase in loading rate, but with the pre-tension increases, the dynamic strength at a certain loading rate decreases accordingly. Moreover, the dynamic strength of naturally saturated sandstone is found to be lower than that of natural sandstone. The fracture behavior of naturally saturated and natural specimens is similar, and both exhibit obvious tensile cracks. The comprehensive micromechanism of water effects concerning the dynamic tensile behavior of rocks with static preload can be explained by the weakening effects of water on mechanical properties, the water wedging effect, and the Stefan effect.

Thermal Shock Effects on Dynamic Deformation Mechanisms in Ti2AlC

2012 ◽  
Author(s):  
R. Bhattacharya ◽  
N. C. Goulbourne
Keyword(s):  
Thermal Shock ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Deformation ◽  
Compressive Loading ◽  
Image Correlation ◽  
Deformation Mechanisms ◽  
Hopkinson Pressure Bar ◽  
High Speed Imaging ◽  
Full Field

The present study is aimed at understanding the effects of thermal shock and associated microstructural features on the dynamic deformation mechanisms in Ti2AlC, a Mn+1AXn phase ternary ceramic. These materials crystallize in a Hexagonal Close Packed (HCP) structure with a c/a ratio greater than 1.67 which results in kink band formations when subjected to loading. In this work, we report the microstructural changes associated with thermal shocking of Mn+1AXn phases and its effects on deformation mechanisms, under dynamic compressive loading. The specimens are heated to temperatures of 220, 550 and 900°C, held at each temperature for 5–10 minutes, and subsequently quenched in water at 20°C to induce thermal shock. The thermal shock resistance and its effect on mechanical properties is investigated by subjecting heat treated specimens to compressive loading at high strain rates (∼1000–4500 s−1) using a Split Hopkinson Pressure Bar (SHPB). The microstructures of thermally shocked specimens are characterized by Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectroscopy (EDS) analysis to reveal the surface morphologies and characteristics. The displacements during the deformation events are captured using in situ high speed imaging, with full-field 2D Digital Image Correlation (DIC) technique. The key microscale mechanisms of deformation are studied using SEM analysis of deformed/fractured specimens.

scholarly journals ‘Seeing’ Strain in Soft Materials

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 542 ◽  
Author(s):  
Zhiyong Xia ◽  
Vanessa D. Alphonse ◽  
Doug B. Trigg ◽  
Tim P. Harrigan ◽  
Jeff M. Paulson ◽  
...  
Keyword(s):  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Color Change ◽  
Soft Materials ◽  
Image Correlation ◽  
High Rate ◽  
Hopkinson Pressure Bar ◽  
Dimethyl Siloxane ◽  
Split Hopkinson ◽  
Pressure Bar

Several technologies can be used for measuring strains of soft materials under high rate impact conditions. These technologies include high speed tensile test, split Hopkinson pressure bar test, digital image correlation and high speed x-ray imaging. However, none of these existing technologies can produce a continuous 3D spatial strain distribution in the test specimen. Here we report a novel passive strain sensor based on poly(dimethyl siloxane) (PDMS) elastomer with covalently incorporated spiropyran (SP) mechanophore to measure impact induced strains. We have shown that the incorporation of SP into PDMS at 0.25 wt% level can adequately measure impact strains via color change under a high strain rate of 1500 s−1 within a fraction of a millisecond. Further, the color change is fully reversible and thus can be used repeatedly. This technology has a high potential to be used for quantifying brain strain for traumatic brain injury applications.

scholarly journals Assimilation of Dynamic Combined Finite Discrete Element Methods Using the Ensemble Kalman Filter

2021 ◽  
Vol 11 (7) ◽  
pp. 2898
Author(s):  
Humberto C. Godinez ◽  
Esteban Rougier
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Peak Stress ◽  
Discrete Element ◽  
Material Behavior ◽  
Model Parameters ◽  
Hopkinson Pressure Bar ◽  
Parameter Values

Simulation of fracture initiation, propagation, and arrest is a problem of interest for many applications in the scientific community. There are a number of numerical methods used for this purpose, and among the most widely accepted is the combined finite-discrete element method (FDEM). To model fracture with FDEM, material behavior is described by specifying a combination of elastic properties, strengths (in the normal and tangential directions), and energy dissipated in failure modes I and II, which are modeled by incorporating a parameterized softening curve defining a post-peak stress-displacement relationship unique to each material. In this work, we implement a data assimilation method to estimate key model parameter values with the objective of improving the calibration processes for FDEM fracture simulations. Specifically, we implement the ensemble Kalman filter assimilation method to the Hybrid Optimization Software Suite (HOSS), a FDEM-based code which was developed for the simulation of fracture and fragmentation behavior. We present a set of assimilation experiments to match the numerical results obtained for a Split Hopkinson Pressure Bar (SHPB) model with experimental observations for granite. We achieved this by calibrating a subset of model parameters. The results show a steady convergence of the assimilated parameter values towards observed time/stress curves from the SHPB observations. In particular, both tensile and shear strengths seem to be converging faster than the other parameters considered.

scholarly journals Study on Impact Damage and Energy Dissipation of Coal Rock Exposed to High Temperatures

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Tu-bing Yin ◽  
Kang Peng ◽  
Liang Wang ◽  
Pin Wang ◽  
Xu-yan Yin ◽  
...  
Keyword(s):  
High Temperatures ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Impact Damage ◽  
Time History ◽  
Hopkinson Pressure Bar ◽  
Absorbed Energy ◽  
Failure Patterns ◽  
Temperature Conditions ◽  
Coal Rock

The dynamic failure characteristics of coal rock exposed to high temperatures were studied by using a split Hopkinson pressure bar (SHPB) system. The relationship between energy and time history under different temperature conditions was obtained. The energy evolution and the failure modes of specimens were analyzed. Results are as follows: during the test, more than 60% of the incident energy was not involved in the breaking of the sample, while it was reflected back. With the increase of temperature, the reflected energy increased continuously; transmitted and absorbed energy showed an opposite variation. At the temperature of 25 to 100°C, the absorbed energy was less than that transmitted, while this phenomenon was opposite after 100°C. The values of specific energy absorption (SEA) were distributed at 0.04 to 0.1 J·cm−3, and its evolution with temperature could be divided into four different stages. Under different temperature conditions, the failure modes and the broken blocks of the samples were obviously different, combining with the variation of microstructure characteristics of coal at high temperatures; the physical mechanism of damage and failure patterns of coal rock are explained from the viewpoint of energy.

Experimental Calibration of ISV Damage Model Constants for Pure Copper for High-Speed Impact Simulation

2016 ◽  
Author(s):  
Yangqing Dou ◽  
Yucheng Liu ◽  
Wilburn Whittington ◽  
Jonathan Miller
Keyword(s):  
High Speed ◽  
Impact Analysis ◽  
Split Hopkinson Pressure Bar ◽  
Internal State ◽  
Pure Copper ◽  
Damage Model ◽  
Hopkinson Pressure Bar ◽  
Experimental Calibration ◽  
High Speed Impact ◽  
The Impact

Coefficients and constants of a microstructure-based internal state variable (ISV) plasticity damage model for pure copper have been calibrated and used for damage modeling and simulation. Experimental stress-strain curves obtained from Cu samples at different strain rate and temperature levels provide a benchmark for the calibration work. Instron quasi-static tester and split-Hopkinson pressure bar are used to obtain low-to-high strain rates. Calibration process and techniques are described in this paper. The calibrated material model is used for high-speed impact analysis to predict the impact properties of Cu. In the numerical impact scenario, a 100 mm by 100 mm Cu plate with a thickness of 10 mm will be penetrated by a 50 mm-long Ni rod with a diameter of 10mm. The thickness of 10 mm was selected for the Cu plate so that the Ni-Cu penetration through the thickness can be well observed through the simulations and the effects of the ductility of Cu on its plasticity deformation during the penetration can be displayed. Also, that thickness had been used by some researchers when investigating penetration mechanics of other materials. Therefore the penetration resistance of Cu can be compared to that of other metallic materials based on the simulation results obtained from this study. Through this study, the efficiency of this ISV model in simulating high-speed impact process is verified. Functions and roles of each of material constant in that model are also demonstrated.

Stress Triaxiality in Chip Segmentation During High Speed Machining of Titanium Alloy

2014 ◽  
Author(s):  
Xueping Zhang ◽  
Rajiv Shivpuri ◽  
Anil K. Srivastava
Keyword(s):  
Titanium Alloy ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Shear Bands ◽  
Stress Triaxiality ◽  
Machining Process ◽  
High Speed Machining ◽  
Hopkinson Pressure Bar ◽  
Static Tests ◽  
Pressure Stress

Beside strain intensity, stress triaxiality (pressure-stress states) is the most important factor to control initiation of ductile fracture in chip segmentation through affecting the loading capacity and strain to failure. The effect of stress triaxiality on failure strain is usually assessed by dynamic Split Hopkinson Pressure Bar (SHPB) or quasi-static tests of tension, compression, torsion, and shear. However, the stress triaxialities produced by these tests are considerably different from those in high speed machining of titanium alloys where adiabatic shear bands (ASB) are associated with much higher strains, stresses and temperatures. This aspect of shear localization and fracture are poorly understood in previous research. This paper aims to demonstrate the role of stress triaxiality in chip segmentation during machining titanium alloy using finite element method. This research promotes a fundamental understanding of thermo-mechanics of the high-speed machining process, and provides a logical insight into the fracture mechanism in discontinuous chips.

scholarly journals Dynamic properties of stainless steel under direct tension loading using a simple gas gun

2018 ◽  
Vol 183 ◽  
pp. 02035 ◽  
Author(s):  
Anatoly Bragov ◽  
Alexander Konstantinov ◽  
Leopold Kruszka ◽  
Andrey Lomunov ◽  
Andrey Filippov
Keyword(s):  
Stainless Steel ◽  
Strain Rate ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Properties ◽  
Tensile Load ◽  
Hopkinson Pressure Bar ◽  
Direct Tension ◽  
Stress Strain ◽  
Gas Gun

The combined experimental and theoretical approach was applied to the study of high-speed deformation and fracture of the 1810 stainless steel. The material tests were performed using a split Hopkinson pressure bar to determine dynamic stress-strain curves, strain rate histories, plastic properties and fracture in the strain rate range of 102 ÷ 104 s-1. A scheme has been realized for obtaining a direct tensile load in the SHPB, using a tubular striker and a gas gun of a simple design. The parameters of the Johnson-Cook material model were identified using the experimental results obtained. Using a series of verification experiments under various types of stress-strain state, the degree of reliability of the identified mathematical model of the behavior of the material studied was determined.

Sign in / Sign up

Export Citation Format

Share Document