The Effects of Dynamic and Pre-Damage on Heterogeneous Materials
Abstract
This research is to determine the effect of damage on the strength and ballistic performance of cement and related materials, particularly concrete. Concrete is a crucial civil engineering material, and is the major structural component material of a wide range of infrastructure. The Institute of Shock Physics (ISP) will contribute the ballistic and dynamic test facilities for the project. The ISP has a range of gas launchers available with bore diameters of 13 mm, 25 mm, 32 mm and 100 mm. Impact velocities range from 100 m/s - 200 m/s on the 32 mm launcher, to 300 m/s – 1400 m/s on the 100 mm launcher, allowing a range of ballistic impact scenarios to be investigated. The Earth Sciences and Engineering (ESE) department has extensive experience in numerical modeling of dynamic events, and will support the development of numerical physics based models. The in house model iSALE has damage models suitable for heterogeneous materials and has been used for modeling planetary impacts on rock. The civil engineering department has quasi-static test equipment and drop weight and Kolsky bar facilities to support the slow and mid range dynamic experimentation. The civil engineering department also has expertise in preparing repeatable concrete and cement samples. There are several mechanisms by which concrete can be damaged. This study will compare the effect of pre-damage and dynamically induced damage. To produce the pre-damage microwaves will be used, a technique employed in the mining and extraction industry. This damage mechanism will be investigated as a means of simulating other forms of damage such as damage induced by high strain rate loading or thermal cycling. Pre-damage using microwaves will allow the sample to be reduced in strength by a desired amount before dynamic studies. In addition, the effect of impact-induced damage will be studied using stepped dynamic loading, where the damage produced by an initial pulse is probed by a second pulse, this will ensure the quantitative linkage between pre-damage and dynamic damage. Understanding and quantifying the effect of damage on the strength of concrete will contribute towards an improved understanding of the behavior of this crucial building material. In general, damage reduces strength, while strain rate and inertia act to increase strength. This interplay makes this research particularly relevant and can inform the requirements for pre-damage of rock or concrete for deep penetration. Current damage models are difficult to validate and often lack a physics based description. Using techniques such as X-ray tomography the pre-damage will be quantified, and post-shock recovered samples will be studied to assess final damage states. These studies will be used to define and populate physics-based materials models in predictive codes such as iSALE and Autodyn. Comparisons of different levels of pre-damage with currently understood models of shock re-shock experiments will allow a separable study of damage and strain rate effects. This is crucial to understanding and developing a physics based numerical model. Time resolved diagnostic techniques in shock physics exploiting X-ray radiography, digital image correlation and interferometry will be used to validate physics-based models for shock and ballistic loading of pre-damaged concrete. Measurable markers including rear surface velocity and penetration depth will be used to compare the results of simulated experiments with real data.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 26, 2016
- Source ID
- HDTRA11510059
Entities
People
- William Proud
Organizations
- Defense Threat Reduction Agency
- Imperial College London