Numerical study on the interaction of the striker and incident bar in the Split-Hopkinson-Bar experiment

Inhaltsverzeichnis (Table of Contents)

• Introduction
• Motivation
• The experimental setup of Split Hopkinson Pressure Bar
• Standard compression test
• Spallation test
• Brazilian test
• Working principle of Split Hopkinson Pressure Bar
• Objectives
• Numerical modelling
• Theoretical background of SHPB test setup
• Model for Validation
• Model behavior
• Stress across length and cross section of incident bar
• Validation
• Parameter Study
• Influence of Poisson's ratio and element size
• Wave Speed
• Loading time, T
• Stress and Strain
• Kinetic energy
• Time-step
• Influence of different element size
• Influence of length and speed of striker
• Variation in length of striker
• Variation in speed of striker
• Influence of inter-facial friction
• Influence of material property
• Influence of diameter of striker
• Results and conclusion
• Numerical model and its validation
• Effect of Poisson's ratio and element size
• Effect of length and speed of striker
• Effect of inter-facial friction
• Effect of material property
• Effect of diameter of striker
• Scope for future studies

Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)

This thesis aims to conduct a numerical study of special issues encountered in Split-Hopkinson-Pressure Bar (SHPB) experiments. The study investigates the discrepancies between theoretical assumptions and experimental/numerical observations, focusing on improving the accuracy and understanding of the SHPB technique.

• Impact of one-dimensional wave theory assumptions on SHPB results.
• Influence of various parameters (Poisson's ratio, element size, striker dimensions, material properties, friction) on wave propagation and stress/strain calculations.
• Validation of the numerical model against experimental data.
• Analysis of discrepancies between rigid body and elastic body assumptions in the model.
• Identification of areas requiring further research to enhance the accuracy and reliability of SHPB experiments.

Zusammenfassung der Kapitel (Chapter Summaries)

Introduction: This chapter introduces the Split-Hopkinson Pressure Bar (SHPB) experiment, a common method for characterizing material behavior under high strain rates. It outlines the experimental setup for standard compression, spallation, and Brazilian tests, detailing the working principle based on one-dimensional wave theory. The chapter concludes by stating the objectives of the thesis, highlighting the need for a numerical study to address inconsistencies observed in SHPB experiments due to deviations from the ideal one-dimensional wave theory.

Numerical modelling: This chapter describes the theoretical background of the SHPB test setup, focusing on the numerical model used for the study. It details the model's validation process, analyzing the model's behavior and the stress distribution within the incident bar. The chapter highlights the importance of considering factors often neglected in simplified models, such as elastic versus rigid body assumptions, and their influence on the accuracy of results.

Parameter Study: This chapter presents a detailed parameter study investigating the influence of various factors on SHPB results. It systematically explores the effects of Poisson's ratio, element size, striker length and speed, interfacial friction, material properties, and striker diameter. Each parameter's influence on wave speed, loading time, stress, strain, kinetic energy, and time-step is carefully analyzed and discussed. The chapter provides a comprehensive understanding of how these parameters affect the accuracy and reliability of the SHPB experiment.

Schlüsselwörter (Keywords)

Split-Hopkinson Pressure Bar (SHPB), high strain rate testing, one-dimensional wave theory, numerical modeling, parameter study, Poisson's ratio, element size, striker dimensions, interfacial friction, material properties, wave propagation, stress, strain, kinetic energy, model validation.

Häufig gestellte Fragen

What is the Split-Hopkinson Pressure Bar (SHPB) experiment, and what is its purpose?

The Split-Hopkinson Pressure Bar (SHPB) experiment is a method used to characterize the behavior of materials under high strain rates. It involves subjecting a specimen to a rapidly applied load and measuring the resulting stress and strain.

What are the different types of tests performed using the SHPB setup?

The SHPB setup can be used for various tests, including standard compression tests, spallation tests, and Brazilian tests. Each test configuration allows for examining different aspects of material behavior under impact loading.

What are the objectives of the numerical study described in this document?

The numerical study aims to investigate special issues encountered in SHPB experiments, focusing on discrepancies between theoretical assumptions and experimental/numerical observations. The goal is to improve the accuracy and understanding of the SHPB technique by analyzing the impact of various parameters and validating the numerical model against experimental data.

What are the key themes explored in this study?

The key themes include the impact of one-dimensional wave theory assumptions, the influence of parameters like Poisson's ratio and element size, validation of the numerical model, analysis of discrepancies between rigid and elastic body assumptions, and identification of areas for future research.

What parameters are investigated in the parameter study?

The parameter study systematically explores the effects of Poisson's ratio, element size, striker length and speed, interfacial friction, material properties, and striker diameter on the SHPB results. The influence of each parameter on wave speed, loading time, stress, strain, kinetic energy, and time-step is analyzed.

Why is numerical modeling important in the context of SHPB experiments?

Numerical modeling allows for a detailed analysis of the SHPB experiment, considering factors that are often neglected in simplified theoretical models. It helps to understand the behavior of the system and to validate the assumptions made in the one-dimensional wave theory.

What is the role of the "striker" in an SHPB experiment?

The striker is a projectile that impacts the incident bar, generating a stress wave that propagates through the bars and the specimen. Variations in the striker's length, speed, and diameter can significantly influence the loading conditions and the resulting stress and strain in the specimen.

How does interfacial friction affect the SHPB results?

Interfacial friction between the bars and the specimen can influence the stress distribution and wave propagation within the SHPB setup. The parameter study investigates the impact of different friction conditions on the accuracy and reliability of the experiment.

What are some of the key words associated with this study?

Key words include: Split-Hopkinson Pressure Bar (SHPB), high strain rate testing, one-dimensional wave theory, numerical modeling, parameter study, Poisson's ratio, element size, striker dimensions, interfacial friction, material properties, wave propagation, stress, strain, kinetic energy, model validation.

What are some areas for future studies identified in this document?

The document identifies the need for further research to enhance the accuracy and reliability of SHPB experiments, addressing the limitations of current models and exploring the influence of factors that are not fully understood.