AFWL-TR-65-161 FWL-TR161

1 AFWL-TR-65-161 FWL-TR161coEXPERIMENTAL STUDY OF STATICAND DYNAMIC friction BETWEENSOIL AND TYPICALCONSTRUCTION MATERIALSG. A. LeonardsPurdue UniversitySchool of Civil EngineeringLafayette, India .. EC LEA R 1!4 c, ! .:. D-TECHNICAL REPORT NO. AFWL-TR-65-161 December 1965 AIR FORCE WEAPONS LABORATORYR esearch and Technology DivisionAir Force Systems CommandKirtland Air Force Base .New Mexico -'I" S .I4~.,-11"ApwL-TR-65-161R , -I Research and Teerhology .. iAR OIC .L r ATOIY-j AIR FORCE WIAC .. Air For-re Systems 0.

2 ,.and-,D~ w .. Kirtlazi Air Force Base$ v. MexicoWhen U. S. Government drawings, specifications, or other data are used forany purpose other than a definitely related Government procurement operation,tb. Government thereby incurs no responsibility nor any obligation whatsoever,ad the fact that the Government may have formulated, furnished, or in any* way supplied the said drawings, specifications, or other deta, is not to beregarded by implication or otherwise, as in any manner licensing the holderor any other person or corporation, or conveying any rights or permission to* manufacture, use.

3 Or sell any patented invention that may in any way berelated report is made available for study with the understanding thatproprietary interests in and relating thereto will not be impaired. Incase of apparent conflict or any othcr questions between the Government'srights and those of others, notify the Judge Advocate, Air Force SystemsCoimand, Andrews Air Force Base, Washington, D. C. of this document is STUDY OF STATIC AN'D D' NAHICFRICTION BETWEEN SOIL AND TYPICAL CONSTRUCTION MATERIALSG. A. LeonardsPurdue UniversitySchool of Ciril EngineeringLafayette, IndianaDistribution of this documentis !

4 FOREWORDThis report was prepared by the School of Engineering, PurdueUniversity, Lafayette, Indiana, under contract AF 29(601)-5204. Theresearch was performed under Program Element , ProjectVi 5710, Subtask , and was funded by the Defense Atomic SupportAgency (DASA).Inclusive dates of research were 1 April 1962 to I April report was submitted 24 November 1965 by the Air Force WeaponsLaboratory project officer lLt John E. Seknicka (WLDC).JO E. SEKNICKAILt, USAFP roject OfficerAYROBERT E. CRAWFORD JOHN W. KODIS(f Major, USAF Colonel, USAFD eputy Chief, Civil Engineering Chief, Development DivisionBranchiiABSTRACTA report is made of research carried out at Purdue University to determine, onthe basis of laboratory measurements, the coefficient of friction between two8sands of different gradation (one vith angular and the other with rcundedparticles) in contact with Portland cement mortar, steel, teflon, and the static tests, loads were applie.)

5 At a uniform rate until sLip occurredin approximately 5 minutes. Dynamic loa4. were applied by means of a shocktube, which produced a gcep-like forcing function; slip usually occurred inapproximately 2 milliseconds or less. It was foind that the coefficients offriction depend on the relative size, shape and surface roughness of the sandgrains with respect to that of the surface in question; when the sliding surfaceis "rough" in comparison with the sand particles, the coefficient of frictionapproaches the coefficient of internal friction of the sand.

6 Both graphite andteflon serve as friction reducers, compared to the plain surfaces, irrespectiveof the rate at which slip is initiated. For plain steel or cement mortar, thedynamic coefficient of friczion was greater than the static coefficient offriction by about 25 percent, unless the static coefficient was such thatsand/sand slip was approached. The angle of shearing resistance of the sandthus provides an upper limit to the coefficient of wall friction at all ratesof page intentionally left OF CONTENTSS ection PageI INTRODUCTION.

7 1II EXERIMENTAL CONCEPT .. 2 General Considerations ..2 Dynamic friction Force .. 4 Inertia Force.. 6 Dynamic Nomal Force .. 6 III .. 7 Sand ..Test Rods ..9IV APPARATUS AND PROCEDURES .. 15 Sample Preparation .. 15 Static Tests ..o ..23 Dynamic Tests ..25V RESULTS ..32 Static friction Tests..32 Dynamic Tests .. 40VI CONCLUSIONS .. 53 REFERENCES .. 55 APPENDICES..A: DETERMINATION OF FORCING FUNCTION.. 56B: USE OF LINEAR VARIABLE DIFFERENTIALTRANSFORMER FOR VELOCITY MEASUREMENTS .58C: SAMPLE CALCULATIONS..62 Statir Tests.

8 62 Dynamic Tests .64 DISTRIBUTION..66vVILIST OF TABLEST able No. PageI. Grain Size Distribution for 60-80 Sand ..7II. Types of Surfaces Tested .. 9 III. Comparison of Is Values for Different Types of TestsUsing 20-30 Sand ..33IV. Values of ps Based on Static Tests with 60-80 Sand ..37V. Values of ps Based on Static Tests with 20-30 Sand ..38VI. Comparison oflis Values..40 VII. 8Ns for Uncapped and Capped Gages at Time of Slip..45 VIII. Values of 4d for 60-80 Sand on Plain Steel ..46IX. Values of 9d for 20-30 Sand on Smooth Mortar.

9 47X. Values of P1d for 20-30 Sand on Rough Mortar..48XI. Values of Aid for 20-30 Sand on Teflon Coated SmoothMortar ..49 XII. Values of 4d for 20-30 Sand on Teflon Coated Steel ..50 XIII. Values of ld for 20-30 Sand on Graphite Coated SmoothMortar ..51 XIV. Comparison of Static and Dynamic Coefficients of friction . 52viLIST OF FIGURESF igure Schematic Diagram of Experimental Concept.. 32. Forcing Functions, F(t).. 53. Failure Conditions at Peakcoi -C3 in the Triaxial Test,20-30 Sand ..84. Failure Conditions at Peakal -03 in the Triaxial Test,60-80 Sand.

10 105. Photomicrograph of Sands (Multiplication x 60) ..116. Test Rods ..o..147. Mold for Sample Preparation..168. Sand "Raining" Tube..179A. Stress Gage and Gage Placing Tool ..199B. Gage Locations ..2010. Sample Headcap ..2011. Extruding the Sample from the Mold ..2112. The Extruded Sample..2213. Sample Housing Showing Alignment Guides and Reaction Ring. 2214. Apparatus for Auxilliary Static friction Tests .. 2415. Proving Ring and Displacement Dial in Position forStatic Tests ..2616. Piston Assembly ..2717. LVDT Mounting.