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ME124 Experiment #7:ME124 Experiment #7:
The ASTM Tensile TestThe ASTM Tensile Test
Spring 2004Spring 2004
Lecture 1Lecture 1
•• Experimental OverviewExperimental Overview•• Presentation of Sample ResultsPresentation of Sample Results
•• Review of Material Properties & DefinitionsReview of Material Properties & Definitions
•• Supplementary Discussion of Specimen Supplementary Discussion of Specimen Fabrication Effects: Casting vs. Fabrication Effects: Casting vs. MaciningMacining
Experimental GoalsExperimental Goals
• Experimental exposure to standard material testing procedures referred to in earlier materials coursework
• Construction of stress/strain curves for different materials from experimental data
• Determination of material properties from analysis of stress/strain curves
• Part 1 : analysis of 6061 aluminum specimens; statistical nature of materials testing
• Part 2: testing of untreated and quenched 4130 steel specimens to observe effect of heat treatment on material properties
The The TiniusTinius Olsen MachineOlsen Machine
Norwegian-born engineer (1845)
Patented first universal testing machine for materials June 1, 1880 in Philadelphia
The The TiniusTinius Olsen MachineOlsen Machine
lead-screw drive
grips
specimen & load-cell
motion controls
load display
Tensile Specimen (“Dog Bone”)Tensile Specimen (“Dog Bone”)
• ASTM specifications call for “dog leg” specimens in testing
• Ensures fracture region will be in center section, away from grips
• 6061 specimens are CNC-milled “in house” from bar stock
• 4130 (hot-rolled, annealed) specimens milled by vendor
grips
grips
Stress Concentration IssuesStress Concentration Issues
Machining defects can lead to stress concentrations whichImpact the tensile testing
Specimen Creation Via Metal Casting**Specimen Creation Via Metal Casting**
**From ENGR1 demo w/ G. Sullivan, Fall 2000
Sample Raw Tensile Test Data (6061 Al)Sample Raw Tensile Test Data (6061 Al)
Data from ENGR1 demoFall 2000
Analysis of StressAnalysis of Stress--Strain Data (4130 Steel)Strain Data (4130 Steel)
elastic modulus (slope)
proportional limit
Data from ENGR1 demoFall 2000
Analysis of StressAnalysis of Stress--Strain Data (4130 Steel)Strain Data (4130 Steel)
Yield Strength defined at 2% permanent strain
Analysis of StressAnalysis of Stress--Strain Data (4130 Steel)Strain Data (4130 Steel)
“Modulus of Resilience” –Total elastic strain energy at proportional limit
Analysis of StressAnalysis of Stress--Strain Data (4130 Steel)Strain Data (4130 Steel)
Ultimate StrengthFailure Stress
Analysis of StressAnalysis of Stress--Strain Data (4130 Steel)Strain Data (4130 Steel)
“Modulus of Toughness” –Total plastic strain energy
Comparative Test Data: Milling vs. CastingComparative Test Data: Milling vs. Casting
Data from ENGR1 demoFall 2000
Tensile Test Results: Milled vs. Cast Specimens
02000400060008000
10000
120001400016000
18000200002200024000
2600028000
0 1 2 3 4 5 6 7 8 9 10 11
Displacement (mm)
Forc
e (N
)
Cast Specimen ICast Specimen IICast Specimen IIIMachined Specimen IMachined Specimen IIMachined Specimen III
Specimen Appearance after FailureSpecimen Appearance after Failure
milled castmilled cast
milled cast
• milled specimen exhibits “necking”, fails at 45° ⇒ shear / ductile failure
• cast specimen exhibits no necking, fails at 90 ° ⇒tension / brittle failure
• dull failure surface appearance of the cast specimen in comparison to milled specimen
Analysis of Test ResultsAnalysis of Test Results
Quantitative ObservationsQuantitative Observations• Comparison of maximum load capacity• Comparison of elongation at failure • Linear elastic range in tensile test; similar elastic moduli• Comparison of size of plastic region
Qualitative ObservationsQualitative Observations• Necking (shear vs. tensile failure)• Fracture Surface Appearance • Homogeneity of specimen
Machining ConsiderationsMachining Considerations
• Solid Mechanics – mechanics of chip formation– stress analysis in tool and work-piece– effect of cutting speeds / feed rate– friction– residual stress in the work-piece
• Heat Transfer– amount of heat transferred into machine (impact of tolerances)– lubrication and coolant– analyze heating of the cutting tool (especially cutting edge)
Casting ConsiderationsCasting Considerations
• Heat Transfer – Solidification time ⇒ filling time and required flow rate – Design for preferential solidification (“chills”)
• Fluid Mechanics– air entrainment– turbulence and mold erosion– aspiration through porous molds – flow resistance and feed distances (required ∆P)
• Materials Science– Solidification shrinkage – Grain structure
Casting Flow PatternsCasting Flow Patterns
evidence of ‘flow separation’ flow lines near the mold inlet