mekanika e shkatërrimit i-koncentrimi i sforcimeve
TRANSCRIPT
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KONCENTRIMI I SFORCIMEVE
Gjendja e sforcuar e trupit të ngarkuar
me forca të jashtme varet nga intensiteti i
forcave të jashtme dhe nga forma e trupit,
përkatësisht nga seksioni tërthor i tij mbi të
cilin veprojnë ato forca.
Çdo ndryshim në seksionin tërthor të
trupit shkakton edhe ndryshim të gjendjes së
sforcuar, ashtu që në trup krijohet një gjendje
e re e sforcuar jo e njëtrajtshme (jouniforme) e
cila në varësi të intensitetit të sforcimeve e
rrezikon trupin nga shkatërrimi.
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Sforcimi
50 kg 50kg
50kg
50kg
A B
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Prezenca e gabimeve, përkatësisht
diskontinuiteteve (kanale, kalesa të
mprehta, vrima, fileta) të ndryshme në
sipërfaqe dhe në brendësi të trupit ku
veprojnë ngarkesa të jashtme gjithashtu
shfaq ndikim në gjendjen e sforcuar të trupit.
Këto diskontiuitete në seksionin e prerjes
tërthore luajn rolin e plasaritjes të cilat
shkaktojnë shpërndarje jo të njëtrajtshme të
sforcimeve.
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F
F
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Sqaruesi: Shigjeta tregon pozicionin e koncentrimit të sforcimeve
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Metoda fotoplastike e shqyrtimit te koncentrimit te sforcimeve
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Geometrically similar specimens
have the same Kt but
different stress gradients
Larger specimens have larger
volumes and larger notch surface
areas of highly stressed material
Important !!!:
Notch Size Effects in Fatigue
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Sforcimi nominal-normal në seksionin I dhe II
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Sforcimi maksimal në seksionin II
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Crack ratio=a:b=1:1
Ks=3
a
b
Crack ratio=a:b=2:1
Ks=5
Crack ratio=a:b=5:1
Ks=11
Crack ratio=a:b=16:1
Ks=33
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F
F
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Skema e koncentrimit të sforcimeve gjatë
lakimit dhe përdredhjes
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Sforcim normal Sforcim tangjencial
F
A
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Koncentrimi i sforcimeve te materialet
duktile (me viskozitet dinamik të lartë)
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Stress Concentration Chart
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Stress Concentrations for Plate with Hole
Stress concentration factor for rectangular plate with central hole. (a) Axial Load. [Adapted from Collins (1981).]
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Stress Concentrations for Plate with Hole (cont.)
Stress concentration factor for rectangular plate with central hole. (b) Bending. [Adapted from Collins (1981).]
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Stress Concentrations for Plate with Fillet
Stress concentration factor for rectangular plate with fillet. (a) Axial Load. [Adapted from Collins (1981).]
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Stress concentration factor for rectangular plate with fillet. (b) Bending Load. [Adapted from Collins (1981).]
Stress Concentrations for Plate with Fillet (cont.)
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Stress Concentrations for Plate with Groove
Stress concentration factor for rectangular plate with groove. (a) Axial Load. [Adapted from Collins (1981).]
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Stress Concentrations for Plate with Groove (cont.)
Stress concentration factor for rectangular plate with groove. (b) Bending. [Adapted from Collins (1981).]
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Stress Concentrations for Bar with Fillet
Stress concentration factor for round bar with fillet. (a) Axial load. [Adapted from Collins (1981).]
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Stress concentration factor for round bar with fillet. (b) Bending. [Adapted from Collins (1981).]
Stress Concentrations for Bar with Fillet (cont.)
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Stress Concentrations for Bar with Fillet (cont.)
Stress concentration factor for round bar with fillet. (c) Torsion. [Adapted from Collins (1981).]
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Stress Concentrations for Bar with Groove (cont.)
Figure 6.6 Stress concentration factor for round bar with groove. (c) Torsion. [Adapted from Collins (1981).]
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