1 Extension of Terrestrial Excavation Mechanics to Lunar Soil Jason R. Florek, M.S. Rutgers University Department of Mechanical and Aerospace Engineering

1

Extension of Terrestrial Extension of Terrestrial Excavation Mechanics Excavation Mechanics to Lunar Soilto Lunar Soil

Jason R. Florek, M.S.Rutgers UniversityDepartment of Mechanical and Aerospace EngineeringJune 5, 2007

2J. R. Florek. Extension of Terrestrial Excavation Mechanics to Lunar Soil. 6/5/07.

MotivationMotivation

Nearly all lunar base designs call for some form of regolith shielding.

Moving regolith also necessary for paving roads and collecting natural resources.

Digging and excavating forces must be well understood for first generation design.

Forces directly related to required power and size, weight and cost of equipment.


Design of EquipmentDesign of Equipment

Grader with extended frame

Combination grader blade Smooth roller

Hemispherical dome wheel

All from Banks et al. (1990).


Modeling Required Modeling Required Cutting ForcesCutting Forces Analytical Models

Two-Dimensional Three-Dimensional Static Dynamic

Finite Element Models Empirical Models


Experiments on Experiments on Lunar Soil SimulantsLunar Soil Simulants

W. W. Boles, W. D. Scott, and J. F. Connolly, Excavation forces in reduced gravity environment. J. Aerospace Engng. 10(2) 99-103 (1997).

Scaled experiment aboard KC 135 aircraft to predict force to fail JSC-1 simulant .

Required force in reduced gravity did not scale by factor of 1/6.

Proposed using results at 1/6 g and 1 g as lower and upper bounds of force.


Experiments on Experiments on Lunar Soil SimulantsLunar Soil Simulants

B. M. Willman and W. W. Boles, Soil-tool interaction theories as they apply to lunar soil simulant. J. Aerospace Engng. 8(2) 88-99 (1995).

Measured average required drawbar forces: 192 N, 522 N and 825 N, respectively.

Values compared to four predictive models. One model: 627 N, 1157 N and 1639 N. Average of other models: 35 N, 112 N, 187 N. All predictive models rejected. Not all necessary parameters provided.


Cutting and Excavating Cutting and Excavating the Lunar Soilthe Lunar Soil

A. Wilkinson and A. DeGennaro, Digging and pushing lunar regolith: Classical soil mechnaics and the forces needed for excavation and traction. J. Terramech. 44(2) 133-152 (2007).

S. Blouin, A. Hemami, and M. Lipsett, Review of resistive force models for earthmoving processes. J. Aerospace Engng. 14(3) 102-111 (2001).

Numerous models for needed digging (drawbar) forces, each with varying complexities.

Authors hold back recommendation until after experimental validation.

Reducing failure plane angle to between 10.4-11.5 deg. creates a match between Gill model and Willman experimental data.


Logarithmic Spiral Logarithmic Spiral Failure PlaneFailure Plane

Locate spiral center.

Moment balance about center.

d2 most difficult distance to calculate.

Minimize pushing forces.

Failure model of Osman (1964).


Cutting ParametersCutting Parameters

Depth Cohesion Surcharge Adhesion

From Blouin et al. (2001).

Fundamental earthmoving equation from Reece (1964).

From Luengo et al. (1998).


Parameter NotationsParameter Notations

[5]-Willman & Boles (1995), [7]-Wilkinson & DeGennaro (2007), [11]-Luengo et al. (1998), [13]-Osman (1964)


Horizontal Force vs. Horizontal Force vs. Tool DepthTool Depth

Depth and tool-soil terms most important. Cutting force in Gill Model arbitrary.


Horizontal Force vs. Horizontal Force vs. Rake AngleRake Angle

Depth and tool-soil terms most important. Negative tool-soil contribution possible for

Swick model.


Horizontal Force vs. Horizontal Force vs. GravityGravity

Depth and tool-soil terms most important for Gill Model.

Only depth term important for Swick model.


Horizontal Force vs. Horizontal Force vs. Cohesion & Internal Cohesion & Internal FrictionFriction

Depth and tool-soil terms most important when changing friction angle.

Cohesion only important for high values.


Horizontal Force vs. Horizontal Force vs. Density & SurchargeDensity & Surcharge

Depth and tool-soil terms most important. Surcharge, cohesion and kinetic terms can in

most cases be neglected.


Depth vs. Soil Depth vs. Soil Density vs. Density vs. Cohesion vs. Cohesion vs. Friction AngleFriction Angle


Parameter Parameter DependenciesDependencies

Failure plane angle is a function of all other angles—rake angle and two friction angles.

Cohesion, friction angles and density are all related to soil depth.

Major problem in determining values for input to equations.


Depth-Varying DensityDepth-Varying Density

Assumed constant density of 1.68 g/cm3 [7]. First model matches density at 9 cm. Second model matches density at 30 cm.


Effect of Density Effect of Density Change with DepthChange with Depth

Assumed constant density of 1.68 g/cm3 (Wilkinson). First model matches density at 9 cm. Second model matches density at 30 cm.


ConclusionsConclusions

Required forces do not scale by 1/6 in reduced gravity.

Although some Earth based models correlate poorly with experimental results, others compare surprisingly well.

Depth and tool-soil terms appear to be most important.

Parameter dependencies should be accounted for in model.

Documents

1 Extension of Terrestrial Excavation Mechanics to Lunar Soil Jason R. Florek, M.S. Rutgers University Department of Mechanical and Aerospace Engineering