iMechanica - explosion - Comments

High Pressure Induced Deflagration to Detonation Transition

Henry Tan — Tue, 06 May 2008 13:48:58 -0400

Title: "High Pressure Induced Deflagration to Detonation Transition in Energetic Materials"

Presenter: Dr Henry Tan

Venue: Pariser H18
School of Mechanical, Aerospace and Civil Engineering
The University of Manchester

Date/Time: 2:30-3:30pm May 7th (Wednesday), 2008

Surfaces, Microstructure & Fracture Group Colloquia, Cambridge

Henry Tan — Mon, 14 Apr 2008 18:22:00 -0400

Sudden energy release around interfaces during quasi-static loading

H. Tan

1st May 2008

Surfaces, Microstructure & Fracture Group Colloquia

Cavendish Laboratory, Cambridge

Non-ideal explosives

Henry Tan — Mon, 14 Apr 2008 18:16:54 -0400

Non-ideal explosives

EPSRC Network (April 2008): Non-Ideal Detonation

Henry Tan — Mon, 14 Apr 2008 18:15:00 -0400

Non-Ideal Detonation - 24th/ 25th April 2008 - Chemical Engineering, Imperial College

An introduction to non-ideal detonation from a commercial explosives perspective. S K Chan, Orica

Effect of ammonium perchlorate mass fraction and particle size in mixtures with nitromethane on the Charge Diameter on Detonation Velocity - Boris Khasainov, ENSMA

Detonation Failure in non-ideal Explosives. P J Haskins, Qinetiq

Pressure Burn rate laws - H Tan, Manchester

Non-ideal heterogeneous explosives and detonation limits - Imperial College TBA

Rolls-Royce project

Henry Tan — Thu, 13 Dec 2007 08:00:44 -0500

Waqas,

Can you put some of your results on this web, with pictures and physical explanations?

Henry.

Biswajit,

Xuchun Ren — Wed, 28 Nov 2007 11:35:21 -0500

Biswajit,

Thanks a lot.

Xuchun

Re: JWL EOS

Biswajit Banerjee — Tue, 27 Nov 2007 19:27:35 -0500

Xuchun,

I think the first step is to understand the basics shock wave theory, i.e., the meanings of isentropic compression, the Hugoniot, the Rayleigh line, etc - in particular, what assumptions are made when we talk about those things. I would suggest a book on gas dynamics such as "Gas Dynamics" by James E. John for the basis ideas followed by "Detonation: Theory and Experiment" by Wildon Fickett and William C. Davis.

Once you understand the basic theory well (and it takes a bit of time to understand the current dogma), you have to decide whether you want to use a Eulerian hydrocode (i.e., compressible CFD code) to solve your problem or a Lagrangian code (e.g. finite elements). If you use a CFD code you will start of with a ceratin pressure, use a Newton-Raphson method to find the corresponding volume (i.e., density, keeping the mass fixed), and iterate until you reach some sort of equilibriation condition. On the other hand, if you use lagrangian finite elements, you will be able to compute the volume change directly. Therefore, you can just take that value, plug it into the EOS and get the pressure.

The literature on these EOSs is diffuse and often classified. You will find some references in

http://www.eng.utah.edu/~banerjee/Papers/fourthmit.pdf

-- Biswajit

Re: JWL EOS

Xuchun Ren — Sat, 24 Nov 2007 19:05:45 -0500

DR. Biswajit,

Thanks a lot. Your reply is helpful. Could you introduce some book or literature about numerical implement of Murnaghan EOS JWL, and JWL++? Thanks.

--Xuchun

Re: JWL EOS

Biswajit Banerjee — Sat, 24 Nov 2007 18:40:12 -0500

I haven't used LS-DYNA for any detonation calculations. The only detontation calculations that I have performed have been using Uintah (for a copper clad rate stick calculation with ANFO). Most of my work has been on deflagration type problems which do not involve very strong shocks.

In our ANFO calculations we have used a Murnaghan EOS for the reactant and a JWL++ EOS for the product and treated both as fluids. The STP density of the product gases was assumed to be 1160 kg/m^3 (which was the same as that of the reactant. In your case you will have to assume rho_0 =~ 1600 kg/m^3.

If your numerical method is velocity driven then the current density is chosen by you (based on the amount of deformation) and the ratio of the initial to the current density gives you the V that you need. On the other hand, if the numerical method is pressure driven then you have to do a Newton solve to get the current density (and hence the current V). That is the reason that you won't find a value for V is the literature - it is either a primary variable or a secondary one and not a parameter.

The initial specific volume is 1/(rho_0). You have to estimate the value of rho_0 based on the temperature and pressure. Hope that helps.

-- Biswajit

re:JWL equation of state

Xuchun Ren — Fri, 23 Nov 2007 12:39:00 -0500

I am sorry. You are right. I make a mistake in my question. What I want know is the "the initial specific volume", which is used in LS-DYNA. It's the value of density of TNT devided by the density of product after detonation in some literatures. It's hard to find this value in literatures.

Could you tell me what's "the compression regime" and which kind of EOS you used for product of TNT detonation. Which software do you used for simulation of detonation and interaction with ambient air? Is the initial specific volume is a essential parameter in such software? I am a newbee of explosions simulation. Any suggestion and comments will be greatly appreciated. Thanks a lot.

Xuchun

Re:JWL equation of state

Biswajit Banerjee — Thu, 22 Nov 2007 23:16:16 -0500

If I recall correctly, V in your equation is either the specific volume (i.e., 1/density) or v/v_0 = rho_0/rho). The units of R_1 and R_2 are determined accordingly. The density of TNT at standard temperature and pressure is about 1600 kg/m^3. The relative volume will decrease as the pressure increases with stiffer and stiffer responses at higher pressures. That seems obvious - so I have probably not understood your question correctly.

The isentropic JWL EOS is designed for the compression regime. You have to be careful with any such model because the range of applicability is usually limited. I believe that the model has been calibrated to approximately 1 GPa.

I don't have the values of the JWL parameters for any particular type of TNT but I'm sure that you can find that in the literature.

-- Biswajit

Industrial Placement

Waqas Ahmad — Wed, 21 Nov 2007 19:17:42 -0500

Industrial Placement

‘Optimising Superplastic Forming Die Shape and Platens for Next Generation Aero Engine Production’

Background

The design of hot forming dies was optimised in the 1980s for the engine types at the time, the knowledge bank has remained constant ever since. The current high by-pass ratio engines are larger and therefore require larger hot forming dies. The increase in size of dies and presses along with the increase in mass of material and thermal efficiency means the cooling time has increased significantly.

The dies are regularly changed for routine maintenance, this includes die surface cleaning or re-cut. However, the current cooling rates are approximately 37°C per hour, this takes 3 to 4 days and consequently has an adverse impact on productivity. The actual die model has been simplified to fit into the scope of the project. The die is manufactured from cronite (HR4), a nickle based alloy. This project is of interest to Rolls-Royce, as the research done will be used by the company to conduct their own investigations on the hot forming process and improve the entire manufacturing process for fan blades.

Aims and Objectives

The project has aim of the project is:

1. To reduce the thermal cycling time during die change over/maintenance through optimised die and platen design.

These aims have been broken down into the following objectives

1. Model current die and platen thermal stress during thermal cycling,

2. Model current die and platen stress during forming,

3. Consider ways of redesigning die to speeding up the cooling press,

4. Define minimum working surface thickness before distortion occurs in normal surface,

5. Develop designs to optimise die shape and to achieve maximum cooling rates

Current Progress

The material used in the die is specially made for Rolls-Royce, as the material must perform at a temperature of 900°C and pressure in the region of 30bars this and the fact that Cronite has a high nickel content makes the material far too expensive therefore, it was beyond the scope of this project to conduct actual experiments on the material. Finite element analysis has been recognised as the best method of analysing the problem.

The finite element package Ansys was chosen to model the current die and platen stresses so far the progress has been reasonable. Several designs have been analysed and the best design will be taken to the next stage and studied in greater detail. The designs will be analysed structurally to determine the effect of the design change on the cooling time and to make sure the die can withstand the working conditions.

2007 Dynamic Compression of Condensed Matter

Henry Tan — Wed, 21 Nov 2007 04:11:26 -0500

2007 Dynamic Compression of Condensed Matter
5 - 6 December 2007
The Royal Society, London

The physical science behind dynamic response holds key challenges.

There is a need to understand materials under the extreme environments encountered in energy generation, conversion and exploitation and in wider industrial and defence applications. This meeting will bring together the community to focus on potentially significant emerging and scientifically challenging areas. It will span research areas informing the dynamic response of materials, new techniques and emerging diagnostics, and their application to the atomic to planetary scale. Keynote invited lecturers will outline the state of their fields of interest. The meeting format will encourage debate to air technical experience and identify future challenges ending with a round table discussion defining the key aspects of the field for the next decade.

Conference Overview

Shock physics in the 21st century
High pressure physics
Response under dynamic loading
Strength and damage
Equations of state
Detonation physics
Isentropic loading
Applications in planetary and space science
Materials at multiple length- and time-scales

About parameters in Jones-Wilkins-Lee equation

Xuchun Ren — Tue, 20 Nov 2007 18:50:26 -0500

Dear Biswajit,

I have a question about a parameter in JWL.

The JWL equation as following

p=A(1-ω/(R1V))exp(-R1V) + B(1-ω/(R2V))exp(-R2V) + ωE/V

The pressure p is sensitive to the relative volume V in the positions near 1 or 2. Could you tell me the approximate value of relative volume V for the TNT? I can not find literature discuss about this value. It will be more helpful if you could give me some literature links. Thanks a lot!

Xuchun

Re: Exact solutions for explosions

Biswajit Banerjee — Wed, 07 Nov 2007 20:42:29 -0500

Xuchun,

The rule of thumb is that the blast wave becomes nearly planar and uniform at a short distance from the source. Therefore, most analytical approaches assume that the problem is essentially one dimensional and involves uniaxial strain. The resulting equation is usually nonlinear as it involves an exponential source term and exact solutions may not be easy to find. For some examples of the equations involved (and probably even some exact solutions in 1-D) you can try the 1983 book by Milan Kubicek and Vladimir Hlavacek which has been republished by Dover in 2008. The book is called "Numerical Solution of Nonlinear Boundary Value Problems with Applications ".

-- Biswajit