Formability Basic terms .1 Flow condition and flow curve

If t h ere is n o flo w cu rve available fo r a p art icu lar m at erial, it can be d et erm in ed by exp erim en t at io n . A t en sile, co m p ressive o r h yd rau lic in d en t at io n t est wo u ld be a co n ceivable m et h o d fo r t h is. If t h e sp ecific d efo rm at io n wo rk w id an d t h e en t ire vo lu m e V o r t h e d isp laced vo lu m e V d are kn o wn q u an t it ies, t h e t o t al d efo rm at io n wo rk W is calcu lat ed o n t h e fo llo win g basis:

2.2.4 Formability

Th e id en tification of form ability sh ou ld on ly be based on th ose cases of m aterial failu re cau sed as a resu lt of d isp lacem en t or cleavage fractu res wh ere n o fu rth er d eform ation is p ossible with ou t failu re. If, th erefore, a m aterial breaks before reach in g m axim u m force as a resu lt of a cleavage 30 Basic principles of metal forming 200 400 600 800 1000 100 300 500 700 sp ec ifi c de fo rm at io n w or k w id 200 400 600 800 1000 100 300 500 700 flo w st re ss k f N mm 2 Nmm mm 3 0,2 0,4 0,6 0,8 1,0 1,2 log. principle deformation g ϕ St 14 St 37 C 35 normally annealed Fig. 2.2.2 Flow curves and curves show ing the specific defor- mation w ork for different materials W V w V k V k i d F g fm F d fm F = ⋅ ≅ ⋅ ⋅ = ⋅ η ϕ η η Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 fract u re, t h is ch aract erist ic m ay be t aken as a p o in t o f referen ce in t h e d et erm in at io n o f fo rm abilit y, fo r exam p le d u rin g a t en sile t est . Ho wev- er, cases o f failu re in wh ich t h e st abilit y crit erio n bet ween t h e o u t er an d in n er fo rces is in d icat ive o f t h e ach ievable d efo rm at io n , can n o t be u sed as a basis fo r d et erm in in g fo rm abilit y. Su ch cases in clu d e fo r exam p le t h e u n ifo rm st rain o f a m at erial wit h m arked n eckin g. Th e fo rm abilit y o f d ifferen t m at erials d iffers even t h o u gh o t h er co n d it io n s are eq u al. Th u s it is t h at so m e m at erials are d escribed as m alleable an d o t h ers as brit t le. Th ese d escrip t io n s are u su ally based o n t h e ch aract erist ics re- vealed in t en sile t est in g fo r fract u res d u e t o sh rin kage o r elo n gat io n . Th e fo rm abilit y o f a m at erial is n o t a fixed q u an t it y, h o wever, it d e- p en d s o n t h e m ean h yd ro st at ic p ressu re p m exert ed d u rin g t h e fo rm in g o p erat io n : Th u s, fo r exam p le, a m at erial can h ave a lo w fo rm abilit y fo r o n e t yp e o f fo rm in g o p erat io n wh ere t h e m ean h yd ro st at ic p ressu re is lo w. Ho w- ever, if a d ifferen t form in g p rocess is em p loyed in wh ich th e m ean h yd rostatic p ressu re is h igh er, th e sam e m aterial can be form ed with ou t p roblem s. Even m arble can be p lastically d eform ed if th e m ean h yd ro- static p ressu re exerted is su fficien tly great.

2.2.5 Units of measurement