Lab 2 TA Presentation Slides.pdf - Lab 2 Compression and...

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Lab 2: Compression and HardnessAdam Werntz & Gaurav SinghalFall 2018Department of Civil and Environmental EngineeringAdapted from Roman Vovchak, Colin Rueb, and many previous presentations1
Compression and Hardness!Experiment #1: Compression TestObserve behavior of materials under compressionCompare with tensile behaviorExperiment #2: Hardness TestLearn Rockwell, Brinell, and Vickers methods and how to convert between hardness scalesInvestigate differences between HRB and HRCRelate hardness to other engineering properties
Experiment #1: CompressionMaterialsCast iron1045 normalized steel7075-T6 aluminumPMMA
SetupLoad cell limit = 100 kNExtensometer limit –15%Displacement rates:Metals: 2.5 mm/minPlastic: 5.0 mm/minDO NOT USE EXTENSOMETER ON PMMAALUMINUM: STOP TEST AT 90KNFor PMMA, use crosshead position to determine strain:You will have to calculate the strain using the crosshead position (i.e. include a sample calculation)00lllε=
Compression vs. TensionE, σy, σu*, and stress–strain plots*Lower bound ultimate stressTrue vs engineering stress and strain
Compressive Failure ModesBucklingMay be due to eccentric loadingBarrelingNot always noticeable to the naked eye
Compressive FailuresBucklingBucklingBarreling
Experiment #2: HardnessNondestructiveCheck heat treatmentAcceptance testingLess accurate—single point measurementMaterials4340 steel7075-T6 aluminumSpecimensFlat surface(no curvature correction)
Multiple Hardness ScalesTypes of IndentersBrinell – 10 mm diameter ballRockwell B –1/16” (≈1.6 mm) diameter ballRockwell C – 120° diamond coneHomogeneity of material influences selectionGrain size influences selection
Brinell (HB)Continuous scaleGood for comparison and plottingLarge indentation10-mm-diam. tungsten carbide ball under 3000 kgfMore destructive, averages out microstructure variationsMeasure diameter of indentationHard to automate
Rockwell (HRB, HRC)7 different scale rangesFor softer and harder materialsSmaller indentation than Brinell: Less destructive, more variation B: 100 kgf, 1/16” steel sphereC: 150 kgf, 120°conical diamond coneMeasure depth of indentation: Easy to automateConversion to HB allowed for: HRC (20–80)HRB (0–100)If necessary, interpolate between values on conversion chart (Table 5 in lab manual)
Mechanics of a Rockwell Hardness Test (HRC)Rockwell hardness is a function of “h
Hardness curvature correctionRecord raw, report correctedCorrection equation based on a specimen of 13 mm diameter Example: The observed Rockwell B hardness is 82 HRB on the cylindrical surface of a 0.5”ø specimenThe curvature correction is equal to +2.5 HRB, and thus the corrected Rockwell B number is 84.5 HRB𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶= 6.50.0582 = 2.42.5The value of the curvature correction is rounded to the nearest multiple of 0.5Must correct hardness data from Lab 1rawCorrection 6.50.05HRB=×

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