Issue 14

D. Firrao et ation very sim Cu and bras y different m ld alloy ring of silver an 1 a FCC dis n twins may b ions on metals some conclu slip band fo haracterized . Also Cu an Ag alloys is in do not prod of grains dist mined, like t identified b

alii, Frattura ed ilar to that s itself. In p orphology c is illustrated d copper in ordered silv e more diffi sions about rmation, eve by low  sf d brass are termediate b uce consider ant one from he yield stres y metallograp

Integrità Strutt of brass, hav articular in a ompared to in Fig. 11 [3] an 18 car er rich solid cult. metals under n at very hig values, mec subject to tw etween the o able deforma another. In s, but it is n hic observat

urale, 14 (2010) ing a stackin gold alloy (1 twins obtain . at gold alloy solution) wi going an exp h deformati hanical twin inning, mor nes of Cu an tions in met such a situati ecessary to c ions.

81-92; DOI: 10 g fault energ 7% Ag) the ed subseque

.3221/IGF-ESIS.

14.09

Go wit

ld alloys hav h intermedia twins was tment after c ery fine twin there is the sformation rphology in w mary of the e above cons  fs values a tenitic stainl ompanied by dency to twin e explosions y in a few in tress parame ending on th

e a behaviou te values bet detected; the old working retrieved in contempora  AuCuI+ hich the det review of the eff iderations all nd high  sf v ess steels, w platelets of ning deform caused by a dividual grain ter macrosco e deformatio

r to deform ween that of y had a ver [16]. the Mattei go ry presence  1 (being  ection of thi ects of explos ow to derive alues, show hich are c  martensite ation of Au small charge s or groups pically deter n mechanism

y quite low presence of v nt an annea

and ery ling

thin trea A v If tran mo Sum Th low aus acc ten Th onl a s dep

, it is possi th a charact

ble to obtai eristic thin p

n a late

losion. Al an on rates. On ning is ind e favoured i d brass. als and may on it is impo onsider eith

d its alloys, w the contrary uced, eventu n the latter. leave their ef ssible to refe er  c,slip or  c

ith , in ally The fect r to ,twin ,

C O

NSIDERATI

ONS AND C

ALCULATIO

NS APPLIED

TO THE FO

RENSIC CA

SE

Ca F

lculations of cr or Al an deforma subject t the case of A ide an Al-allo

itical resolved d Al alloys, tion is practi o deformatio l we must c y fragment r

shear stress fo  c,slip is to b cally impossib ns with spee onsider a  c, etrieved durin

r twinning e taken into le.  c,slip incr ds up to 55 s slip range var g the corone

ve high  sf v tion rate eff d stress of m and 6 MPa. corpse are vi

account bec eases due to -1 show an in ying at least r autopsy of

ause they ha high deforma crease of yiel between 0.6 Mr. Mattei’s

alues and th ects: tests on ore than 100 Multiple slip sible in Fig. 1

erefore twinn Al monocrys %. Conseque bands dete 2.

ing tals ntly cted

in ins

Fig

Fi

gure 11 : Thin ring, observe (NH 4 ) 2 S 2 O tead, as it reg  martensite. ive approxim approximate oming infini  c,twin =

twins formed i d by Scanning 8 (10%)+NaC ards austenit In the literat ate values ta relation bet tesimal when  sf / 2b 1

n the Mattei g Electron Micr N (10%) solu ic stainless s ure no suitab king into acc ween  c,twin a the distance

old alloy (18 c oscopy; etchin tion in water. teels, we mus le  c,twin value ount some of nd  sf is deriv among the d

arats) g:

ure 12 : Multip fragment re Mr. , even if th for austenit s listed in Ta t advanced b creases: win

le slip bands trieved during Mattei’s corps ere might be ic stainless st b. 1, as show y Suzuky an

formed in an a the coroner a e: Keller etcha the contemp eels; howeve n below. d Barrett [6],

luminium allo utopsy of nt. orary forma r it is possibl

y

t refer to  c,t s were found the  sf value ed from tha islocations in

Ins of der An bec

tion e to

omitting a t

erm

(3)

87