# Presentation: 574305

## State-of-the-Art Technological Developments in Concrete – Computational Modeling, Emphasis on Blast EffectsDaniel G. LinzellAssociate ProfessorDepartment of Civil and Environmental EngineeringPenn State University 

**Notes:**
Good afternoon

I’m Dan Linzell, Associate Prof of CEE @ PSU and last speaker.

Here to talk about computational work – innovative concretes (materials in/on the mix) – with a focus on blast (other items presented though)

## Acknowledgements	

**PSU**
**Faculty - James Anderson, Lyle Long, Barry Scheetz, Andrea Schokker**
**Grad Students – Emre Alpman, Abner Chen, Andrew Coughlin, Eric Musselman, Richard Myers, Thara Viswanath**
**Sponsors**
**PSU Applied Research Lab**
**Office of Naval Research**
**AFRL**
**APCI**
**Ogden Tech.**
**Kontek Industries**

**Notes:**
Before get started acknowledge everyone involved

Lost of faculty involved with computational work indirectly/directly

Couldn’t be done without past/current students

Also no without sponsors

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (Polyurea)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
First quickly review overall objectives – remember emphasis computational (numerical)

Background:

FEA – basics of approach (ALL solid modeling presented here accomplished this way)

Polyurea – the S’s talked a lot about the concrete, no bkgd needed.  I will discuss OTHER material placed onto concrete (and other things) – polyurea.  INNOVATIVE for blast protection.

CFD – development of blast waves using codes developed @ PSU.  Codes have been shown to effectively predicted the initiation and advancement of blast waves around rigid objects. Work is underway to expand the ability to incorporate chemical reactions that occur within the blast can be included in the simulation.  Will demonstrate their effectiveness in a minute.

Solid modeling – utilization of advanced commercial FE codes to model components to which polyurea being affixed to (LONG FIBER CONCRETE), along with modeling the polyurea itself.  Once confidence established in the models they will be used to examine the possibility of tailoring the coating placement onto the material for certain applications (e.g. design the coating for specific mitigation/performance applications).

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (****Polyurea****)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
FEA

## Background – Finite Element Analysis (FEA)

**What is FEA?**
**Computer-based numerical technique (1940s/50s)**
**Calculating strength and behavior of engineering structures**
**Deflection, stress, vibration, buckling, many other items**
**Small or large deflection effects**
**Elastic, inelastic, plastic material response**

**Notes:**
“New” technique?

Why everywhere?  ROBUST.

## FEA

**Structure is broken down into many small simple blocks or ****elements**
**Behavior of individual element described with relatively simple equations**
**Element behavior equations combined**
**Large set of simultaneous equations describing behavior of whole structure (EASY FOR PCs)**
**After solving equations, extracts behavior of individual elements**
**Used to get stress, deflection, etc. anywhere**

**Notes:**
What is FEA?  Exactly what it sounds like.

Figure out equations of pieces, combine to form equations of whole, separate again to get response of pieces (keep together for whole).

## Tip Of Cover Plate

**Tip Of Cover Plate**

**Beam**

**Column**

**Cover Plates**

**Peak Difference = 9.89%**

**Experimental**

**Numerical**

**Notes:**
Some schematics showing how used.

Each shape = an element.  Types selected a function of needs, available tools, time, skill, etc.

HERE – wanted DETAILED info on response of specific steel connections, why looks the way it does.

Results for app shown - displacements

## FEA

**Why useful?**
**Can evaluate behavior of complex structures using systematic, proven approach**
**Fewer assumptions built into analysis?**
**Relatively efficient – allows for parametric/optimization studies relatively efficiently**
**Able to be performed using basic PC platforms**
**Economical? Depends.**

**Notes:**
Why everyone use it?

Systematic, fast and cheap IF USED EFFECTIVELY.

## FEA

**Types of Analyses?**
**Discussed earlier**
**Deformations – large vs. small**
**Material response – elastic vs. inelastic vs. plastic**
**Response**
**Static, dynamic, blast, impact, contact, buckling, transient, etc.**
**Able to be performed using rather basic PC platforms**

**Notes:**
How applied?

FUNCTION OF NEEDS – large vs. small defs (defs affect response affect defs etc.)

FUNCTION OF RESPONSE BEING INVESTIGATED

Can use PCs to do this.

## FEA

**Possible pitfalls?**
**Model creation and discretization (element #)**
**“****Always make it look like the picture”**
**Loads**
**Correctly calculated?  Applied? All included?**
**Boundary conditions (“supports”)**
**Correctly accounted for?  Applied?  All included?**
**Material behavior**
**Correctly represented *****throughout its anticipated load range***

**Notes:**
What could go wrong?

Many things – TOO COMPLEX FOR NEEDS or wrong things used, loads wrong – everything wrong, how support?

FOCUS TODAY – correct representation of materials (especially innovative materials for blast) – MUST GET IT RIGHT.  Big part of what we’re doing.

## FEA

**How become proficient?**
**Practice, practice, practice**
**Understand theory behind FEA method and *****how computer forms and solves the problem***
**Attend workshops and conferences organized by software vendors, professional groups**

**Notes:**
GET GOOD BY DOING AND LEARNING

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (Polyurea)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
Done w/ FEA, now discussed background related to other innovative material.  PLACED ONTO CONCRETE.

## Background – Innovative Materials 

**Drs. Scheetz and Schokker**
**Concrete**
**Me**
**Polyurea**

**Notes:**
AGAIN, the Ss discussed innovative concrete.  I discuss coating.

## Background – Polyurea

**Polyurea – *****innovative protective coating system***
**Introduced by Texaco in 1989**
**Known Advantages vs. Polyurethanes (traditional coatings)**
**Applications**
**DoD – Civil Infrastructure**
**DoD – other apps**
**Army/Navy – Spray on armor (Humvees)**
**Navy – Ship hulls (U.S.S. Cole)**
**Other – Civil Infrastructure**
**Rail cars**
**Water storage tanks**
**Chemical plant infrastructure**
- Sources:
- PCI: _[http://www.pcimag.com/CDA/Archives/779f754db76a7010VgnVCM100000f932a8c0](http://www.pcimag.com/CDA/Archives/779f754db76a7010VgnVCM100000f932a8c0)_
- DefenseReview.com: _[http://www.defensereview.com/article502.html](http://www.defensereview.com/article502.html)_,
- _Polymer Materials for Structural Retrofit_, Knox et al., AFRL

**Notes:**
Brief info related to polyurea – somewhat recently developed system; “epoxy paint”; has been shown to have clear advantages over more traditional urethane coatings systems, including: Faster reaction times; Insensitivity to moisture/humidity; Adhesion – wet substrates; Mechanical properties – tensile strength, MOE; Abrasion/heat/fire resistance; Stability; VOCs, Environmental Protection

Number of public domain sources indicating DoD uses for this coating along with other evidence of uses in civil infrastructure – show blast resistance is enhanced. 

None discuss mechanics related to how system works with substrate (ANY) to help with designing optimal coating apps. 

We are exploring the mechanics of the behavior to assist with design optimization for polyurea on materials to mitigate IED effects.

## DoD applications – Polyurea
AFRL
ERDC-WES
Army
Navy
Pentagon
Retrofit
Public domain?

Source: Polymer Materials for Structural Retrofit, Knox et al., AFRL; Army Times

- AFRL
- ERDC-WES
- Army
- Navy
- Pentagon
- Retrofit
- Public domain?
- Source: _Polymer Materials for Structural Retrofit_, Knox et al., AFRL; _Army Times_

- Untreated stud wall

- Coated with polyurea

**Background – Polyurea**

**Notes:**
Why are we focusing on polyurea? Its been examined and used by the DoD in a number of applications and has been shown experimentally to provide effective blast mitigation and component strengthening.  However not much public domain work has occurred w/r/t the mechanisms behind how it works.  

We’re attempting to examine these mechanisms to tailor polyurea-substrate system performance in the public domain.

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (****Polyurea****)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
Now want to do a short bkgd on where our loads come from – REMEMBER important to getting computational results right (if loads are not accurate NOTHING will be)

## Blast Simulation CFD Method (Long, PSU)

- Unstructured-grid, time-accurate Euler code
- Finite volume, Runge-Kutta time marching
- Code is called PUMA2
- Has been in use at Penn State for many years, thoroughly validated on a wide range of problems

**Notes:**
Overview of the CFD approach used by my colleagues with the PUMA2 code

ALL I’M GOING TO SAY – have any questions contact the PI.

## Blast CFD - Assumptions

- 75 lbs. of TNT
- Explosive is spherical in geometry
- Uniform explosion

**Notes:**
Details on the detonations modeled using Long’s CFD.

Why selected?  Have some experimental data from blast testing in Canada that we’re comparing to – charge size and distance from those tests.

This size is the size used for the blast tests in Canada, Eric told me that they tried several combination of the amount of TNT and the distance btw the explosive and the plate, and they ended up using this weight for most of their tests to get the effect they wanted.

## Blast CFD - Initial Pressure Profile

**Blast CFD - Initial Pressure Profile**

**Notes:**
Here are some results from the PSU runs of this blast.

Initial pressure profile – nondim pressure and distance from charge center

## Blast CFD - Pressure History

**Blast CFD - Pressure History**

**Notes:**
Pressure time histories at varying radial distances from the charge ctr.

## Blast CFD – PUMA2 vs. ConWep

**Notes:**
To further provide confidence in the CFD code have starting comparing it to CONWEP (CONventional WEaPons) – pressure profile development code.  Dyna can use CONWEP to develop loads.

Keep in mind the CFD code is much more capable than CONWEP of handling blast/solid interactions

Again, 75# charge wt used (tests) and good agreement show for overpressure vs. radial distance

## Blast CFD - Simulations  w/ Plate

- Plate Dimensions (60in by 60in)
- 75 lbs. of TNT
- Plate located approx 3 ft away from the explosive

**Notes:**
As the CFD relates to the items we’ve been looking @ - using PSU codes to develop pressure AND temperature time-histories @ the center of a RIGID plate matching where we’re modeling on the solid-mech side.

Relevant parameters again given – including location of charge relative to plate.

## Blast CFD - Loading History @ Center

**Blast CFD - Loading History @ Center**

**Notes:**
Info from the PSU CFD code that is used as loads in our solid-mech models

CAN AND WILL DO TEMPERATURE

## Background – Fluid/structure simulations w/ CFD

**Interaction**
**Loosely coupled**
**Mechanisms behind protection?**
**Parameters to control performance?**

**Background – ****Fluid/structure simulations w/ CFD**

**Notes:**
A little more info on the CFD involvement with the simulations that are going to be presented next

CFD info that is generated is currently being loosely coupled commercial FEA codes so that response of the structure to a blast event can be measured

Commercial codes – ABAQUS and LS-Dyna – both being studied here.

Intent of ALL studies is to examine the mechanisms behind the protection system that polyurea creates onto its substrate and then to attempt to study parameters that can control its performance 

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (****Polyurea****)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
Now will talk about ongoing research work – first relates to the items that the Ss talked a lot about.  Long fiber concrete and material models that are being examined and their effectiveness for predicting impact/blast response.

## Focus Areas – Innovative Concretes

**Numerical fluid/structure program**
**Material models**
**Component representation**
**Response of various components under impact and blast loading**

**Notes:**
Will now discuss the work that is being done in relation to the innovative concrete from the modeling side – fluid/structure interaction

Three main areas as shown

## Focus Areas – Innovative Concretes

**Numerical fluid/structure program**
**Material models**
**Component representation**
**Response of various components under impact and blast loading**

**Notes:**
Material models are a BIG emphasis – concrete (Orthotropic? Anisotropic? Under blast)

## Long Fiber Concrete – Material Model

**Create and validate material model **
**Accurately describes behavior of long carbon fiber reinforced concrete**
**Dynamic loads – Impact 1****st**** **
**LS-Dyna**

**Notes:**
Computational w/r/t material models has goal of developing a validated long fiber model in LS-Dyna that works for dynamic events (HIGH strain rate – 1st impact, then blast)

## Long Fiber Concrete – Material Model

**Selected Model – Cowper-Symonds (Tension and Compression)**

**Notes:**
The material models that were initially selected for impact apps were determined from an extensive lit search and some additional experimental data generated @ PSU (Ss discussed) – NOT NECESSARILY @ STRAIN RATES THAT WERE NEEDED.  As a result a previously derived and heavily referenced/validated material model was selected for the fiber concrete IRRESPECTIVE of load orientation (T or C).  A LOT OF WORK.

## Focus Areas – Innovative Concretes

**Numerical fluid/structure program**
**Material models**
**Component representation**
**Response of various components under impact and blast loading**

**Notes:**
With this initial selection the long fiber computational work moved to application phase WITH CONTINUED VALIDATION

## Long Fiber Concrete – Impact

**Model Instrumented Impact**
**Element selection and discretization (element #)**
**How represent fibers?**
**Boundary conditions**

**Notes:**
Again, applied to impact 1st.  Tests were as described by Ss. Intent was to come up w/ accurate model construction method AND material representation method for long fiber concrete

## Long Fiber Concrete – Impact

**How represent fibers?  ****Discrete****.**
**Concrete - solids, reinforcement - truss (perfect bond)**
**Rate effects important**

**Long Fiber Concrete – Impact**

**Notes:**
Looked @ different fiber representation methods for impact tests shown earlier.  Intent to predict response and failure patterns over a wide strain range.  

One modeling approach – SHOW EVERYTHING SEPERATELY

Plot shows sensitivity to strain rate and (want to match actual time and displacement) and color plan view shows predicted crack pattern (response predicts EXTREMELY sensitive but crack pattern pred good).

## Long Fiber Concrete – Impact

**How represent fibers?  ****Smeared****.**
**Rate effects again important**

**Long Fiber Concrete – Impact**

**Notes:**
Another modeling approach – DO EVERYTHING TOGETHER/SMEARED

Plot shows sensitivity to strain rate and (want to match actual time and displacement) and color plan view shows predicted crack pattern (again, response predicts EXTREMELY sensitive but crack pattern pred still good).

## Long Fiber Concrete – Impact

**How represent fibers?  ****Strain erosion with nonlinear springs****.**

**Long Fiber Concrete – Impact**

**Notes:**
Third modeling approach – focus more on response within material and material failure (strain erosion) and how fibers assist after localized failure (springs bridge cracks)

Again, able to show somewhat similar crack pattern but could NEVER get reasonable response preds

## Long Fiber Concrete – Impact

**Model Instrumented Impact – Work for Blast?**
**Controlled by post failure response – 2 selected models NG**

**Long Fiber Concrete – Impact**

**Notes:**
Intent was to take 2 of 3 promising approaches from impact and move to blast with minimal mods.  When attempted for work Ss described DID NOT WORK – blast material response differed from lab impact.  Post failure resilience was shown to be substantial enough to render recommended mat’l model and modeling approach combos ineffective.

## Long Fiber Concrete – Blast

**Model Blast**
**How represent fibers? ****Tension****.**
**Available material models in LS-Dyna**
**First static, then dynamic**

**Notes:**
Now moved to blast focus.

Recognized that, while comp response IMPORTANT AND AFFECTED BY FIBERS, real control of failure was tensile response.

Stepped back to look @ tensile response preds using LS-Dyna canned constitutive models under static loads with long fibers (REEXMAINED).  Then moved back to dynamic (BLAST)

## Long Fiber Concrete – Blast

**Model Blast**
**Normally reinforced**

**Notes:**
Again – once back to blast stepped back and reevaluated ability to predict normally reinforced response.  Material models concrete and reinforcement and methods for representing (discrete – SHOWN – vs. smeared?).

## Long Fiber Concrete – Blast

**Model Blast**
**Normally reinforced**

- Crack Pattern

**Notes:**
Did behavior match expected? (NOTE – EXPERIMENTAL WORK FORTHCOMING).  Here appears yes - TENSILE.  Move to blast.

## Long Fiber Concrete – Blast

**Model Blast**
**With long fibers**
**LS-Dyna Mat’l Model 179**

- H0

- L0

- H15

- L15

**Notes:**
With blast – need to change model?  Looked at different ones (#’s – different models.  NOT NECESSARILY DEFINE AS CONCRETE IN PGM).  Again – behavior match expected AND, if fibers included, behavior match expected?  Appears yes – TENSILE.

NOTE:  1⁄4 sym plots shown.

## Long Fiber Concrete – Blast

**Model Blast**
**Application – barrier systems**

**Notes:**
Still studying and intent to predict response for various structures (barrier shown here) under blast WITH FIBERS AND WITHOUT.

Shows barrier system damage under blast event.

Also WITH COATING AND WITHOUT.

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (****Polyurea****)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
Good bridge to last section – COATING STUDIES.

## Focus Areas – Innovative Coatings

**Numerical fluid/structure program**
**Material models**
**Comparison of ABAQUS and LS-DYNA**
**Effect of polyurea on plate under blast loading**

**Notes:**
Will now discuss the work that is being done in relation to the polyurea from the experimental and solid modeling side – fluid/structure interaction

Three main areas as shown

## Focus Areas – Innovative Coatings

**Numerical fluid/structure program**
**Material models**
**Comparison of ABAQUS and LS-DYNA**
**Effect of polyurea on plate under blast loading**

**Notes:**
Will now discuss the work that is being done in relation to the polyurea from the experimental and solid modeling side – fluid/structure interaction

Three main areas as shown

## Material model - Polyurea

- Mie-Gruneisen equation of state (Fuentes 2006)
**Hydrodynamic material model,  F(density, internal energy)**

- C0 and s : material constants

- : material constant

- : reference density

**Notes:**
Similar to work with long fiber concrete, a lot of work (experimental – not mentioned here – and computational) going into getting the right material model for polyurea in tension and compression under blast loads.  EOS approach – volumetric, hydrodynamic.

One selected constitutive model that appears to have promise in certain apps shown.

Gamma is called Gruneisen ratio
Em is called specific energy
Eh is called Hugoniot energy and is defined as the equation above
Ph is called Hugoniot pressure and is defined as the equation above
MG EOS determines the volumetric strength of the material. Hence, the polyurea is modeled hydrodynamically.

## Numerical program

- Abaqus - Explicit
- LS-Dyna
- PUMA2

**Notes:**
One aspect of these studies not discussed previously was the need to see if the right tool being used – two are popular for research for our (uncoupled) application.  LS-Dyna and ABAQUS/Explcit.

Spent time in association with the polyurea work determining which was best – w/ PSU CFD code.

Spend some time discussing.

## Focus Areas – Innovative Coatings

**Numerical fluid/structure program**
**Material models**
**Comparison of ABAQUS and LS-DYNA**
**Effect of polyurea on plate under blast loading**

**Notes:**
Will now discuss the work that is being done in relation to the polyurea from the experimental and solid modeling side – fluid/structure interaction

Three main areas as shown

## Numerical analysis-ABAQUS and LS-DYNA

**Notes:**
Beam model: compare abaqus and lsdyna by looking at the dynamic response of the beam under impact loading.  STEPPED BACK AGAIN.

NOTHING we could find detailed accuracy – camps typically exist.

Went with a BASIC problem with BCs similar to ours.

Able to establish confidence in both – as expected.

## Pressure time-history 

**Notes:**
Step loading.  1ms rise and fall. 4ms hold.

Material model MAY NOT BE ACCURATE – still apples to apples?

## Displacement

**Notes:**
Displacements quite good during and after impact

## Von Mises Stress

**Notes:**
VM stresses – similar profiles but “lag”. ABAQUS and Dyna are NOT the same – ABAQUS uses direct sparse solver in ABAQUS/Standard, explicit time integration in Explicit for transient dynamics and quasi-static analyses.  LS-Dyna – more traditional solving techniques.

## Internal energy

**Notes:**
Looking at a global and volumetric parameter, Internal energy.

Shows basically the same – may have local diffs but integrated performance is repeatable.

NOW COULD MOVE AHEAD – SELECT ONE WHICH HAS BEST MATERIAL MODELS?

## Focus Areas – Innovative Coatings

**Numerical fluid/structure program**
**Material models**
**Comparison of ABAQUS and LS-DYNA**
**Effect of polyurea on plate under blast loading**

**Notes:**
Will now discuss the work that is being done in relation to the polyurea from the experimental and solid modeling side – fluid/structure interaction

Three main areas as shown

## Configuration of the model

**Notes:**
Explanation of charge position for future discussed work – Ss discussed tests.

## Comparison of displacements

**Notes:**
Used PSU CFD for reasons discussed earlier – LS-Dyna has CONWEP.  Why not use – see here.  Validated by tests.

From the observation of the results, it is inferred that the pressures generated by puma2 are larger than pressures generated by conwep.  REMEMBER – inaccurate constitutive props, defs NEVER this high w/o fracture.  However wanted to see diff.  WILL modify with recently produced mat’l model data for the steel.

## Effect of polyurea on plate under blast loading

- Thickness of coating: 0”, 0.25”, 0.5”
- Polyurea (Air Products)
- Mie-Gruneisen Equation of State
- Load: PUMA2 CFD code

**Notes:**
NOW present some polyurea results. EFFECTS OF COATING THICKNESS (OTHER ITEMS BEING STUDIED – INTENT TO DEVELOP DESIGN CRITERIA)

Models that have been developed have been focusing on the parameters listed here:

Examining three coating thicknesses – range obtained from literature review and discussions with DoD personnel regarding effectiveness of larger thicknesses along with recognition of final application for project (IED mitigation)

They simulated steel plates of the thickness of 0.5” with the polyurea coating of the thickness of 1”. I followed the proportionality of thickness between the steel and polyurea in this paper.

## t = 0”

**Notes:**
Following slides show LS-Dyna prediction of effects. UNCOATED 1st then increasing coating thickness.

This shows that plate was torn apart under the blast loading.
The edges failed (fracture). I think that it is due to the boundary condition (fixed). 

## t = 0.25”

**Notes:**
Polyurea AWAY from blast.

The edges fractured, but it wasn’t torn apart. Perfect bond betw substrate and poly.

## t = 0.5”

**Notes:**
Same as previous one. Fractured but it was not torn apart.

## Deflection at the center

**Notes:**
It is shown that the polyurea can prevent the steel being torn apart, but the deformation is still large. Uncoated fracture @ about 1.5 ms.

## Kinetic energy

**Notes:**
Polyurea can reduce the kinetic energy which is mv^2/2, implying reducing the momentum caused by the blast loads.

## Objectives - COMPUTATIONAL	

**Background – Finite Element Analysis**
**Background – Innovative Materials (Polyurea)**
**Background – CFD Simulations**
**Examination of innovative concretes under simulated blast loads – long fiber concrete**
**Coating materials to help make structures blast/impact resistant - polyurea**

**Notes:**
Discussed these items.

## Summary

**Summary**

**Notes:**
Quickly summarize our project plan pictorially.  

Our intension is to take existing expertise related to development of blast/shock wave information onto various structures, expand that knowledge base to include chemical reactions that would occur in an IED event, use this information in conjunction with numerical and experimental data to develop a fully coupled numerical system that will allow us to assist with “designing” polurea systems for components that provide optimal blast mitigation.

## Questions?

- Contact Info
- Daniel Linzell
- _[DLinzell@engr.psu.edu](mailto:DLinzell@engr.psu.edu)_