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

Milling ProcessMilling Process

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

Removal from the MoldRemoval from the Mold

CloseClose--Up of the Metallic StructureUp of the Metallic Structure

The (The (AmostAmost) Finished Specimen) Finished Specimen

A Finished Cast SpecimenA Finished Cast Specimen

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

Coming in Lecture 2….Coming in Lecture 2….

Effects of Heat Treatment on Effects of Heat Treatment on Material Properties of 4130 SteelMaterial Properties of 4130 Steel