Question

The drawing of the sample is not that important and a compact specimen is there in the notes. a. The stainless steel and polystyrene rulers in Example 5.2 are loaded as cantilevers of length 250mm. Both have sharp transverse scratches of depth 0.2 mm, near the base of the cantilever on the tensile side. For this surface crack geometry, assume the factor Y in equation (8.4) is 1.1. The fracture toughness Kıc of steel and polystyrene are 80 and 1 MPa.m", respectively. Calculate the stress needed to cause a fast fracture in each case. Will the cantilevers fail by yielding or by fast fracture? b. A compact tension specimen, as in Figure 8.4, is manufactured from an Al alloy with dimensions w=50mm and b=20mm, with a sharp pre-crack of length c=10mm. The maximum load capacity available on the test machine is 50 kN. Is the machine capacity sufficient to fracture the alloy, if its fracture toughness is 25 MPa.m”? ?

Answer 1

Solections rulur. means C=0.2 mm -4 F2X10m = IMPa.m's Given for Both Stainless steel folepetyse ne el = 250mm = 0.25m transverse scratch depth Y Crowtaut) = p. 1 kic steel = 80 mPa.ml kic folyetyrene fracture "The stress for Steel in given below by standard equ as given = fracture Sac 80 Ź 2.9 GPa 1.1.Jā X2X104 from standard charts lield strength of stainlus kic 20 of steel of Stainless steel varies from 200 - 900MPa Hence » Gield for stainlus steel hence stainless steel ruler yield before it fractures. fisteel

Solections rului 2010 m kic 1 MPa.ml Güven for Both Stasiuless steel & folupstysene el = 250mm = 0.25m transverse scratch def th means C= 0.2 mm Y Comtaut) = 1.1 kic steel = 80 mPa.ml folystyrene fracture The stress for stainless steel is given Lelow by standard equ kic fracture liste 80 = 2.9 GPa 1.1. ja X2 X104 from standard charts lield strength of al given = 2o f steel ofre Stainless steel varies from 200 - 900MPa Hence of steel » Geld for stainlus steel hence stainless steel ruler yield it fractures. before

Now for FLINTEN folyetyrene rules e coibent av ...to polystyrene Kicho al Clinic tiñca DX 10.6.8.12.305 XX2X10 4 2.36 MPa at fracture etriss 36 MPa for Standard charts Yield et rength about 50-60 MPa hence yield> of for folystyrenie means this ruler gets freeture Polystyrene from her from el + Before it yoelds. ? hayy ( Win Love!!:1) ... bots. 133 posto so in