Issue 14

B. M

. Chiaia et alii

, Frattura ed In

tegrità Struttural

e, 14 (2010) 45

-51; DOI: 10.322

1/IGF-ESIS.14.0 5

sno the alo Th ava dis

w cover. Dy presence of ng the extens e use of crac lanche slab i continuities (

namic crack discontinuou ion of the sn k arresters is nto smaller s void) into the

propagation s weak zone ow slope. a first step labs, causing snowpack –

into a dry sn s (equipped towards a ne small avalan the snow crack

ow slab is m with differen w idea of ac ches to prop arresters - dis

odelled to as t shapes and tive avalanch agate with l tributed alon

sess the poss geometries e protection ess catastrop g the snow sl

ibility of crac of artificial v : the target i hic effects th ope release a

k arrest thro oids) distribu s to split a l anks to artif rea.

ugh ted arge icial

T H

E PRINCIPL

E OF CRAC

K ARREST

spe W ed.

R , the struc odynamics, t etic energy d

hen t and r (shad

he driving fo apid crack pr ed area in Fi

rce G for cr opagation oc g. 1a) is conv

ack extension curs (Fig. 1. erted into ki

exceeds the a). According netic energy.

material cra to the first The magnitu

ck resistance law of therm de of the kin

ture is unsta he excess en ictates the cr

ble, ergy ack

(a) acture propag he driving fo xtension of rack arrest. T Arrest does re energy. Ar arrest toughn ned by the etry. Figs. 1a e crack drivi e kinetic ene

(b) pagation and a l to the mat ck falls below n K I = K Ic . I ecause the s sistance curv than the true ring crack p l resistance w effect of kin ition of ener

Figure 1 a quasi-static energy avail ck arrests. Fi ve, it eventu rgy that can rgy has been ference betw perty, where ves represen rgy balance m ere, as usual, E k is the kin nsidering the ditions can b )( tK I  ere v is the pagation ( dyn ed by means an infinite b nsity factor )( I tK  k

: Balance of en case, a crack able for an i g. 1b illustrat ally crosses t be converte dissipated. T een K Ia and as K Ia depen ting K I and G ust be mod F is the wor etic energy. stage of cr e written as: )( v K ID crack speed amic crack-res of optical m ody or short and the dyna d dE dA dU dA F

ergy for: (a) fr is stable if t ncremental e es a simple c he R curve. d into fractu he apparent K IA is gover ds on geom values. If th ified to includ

ation, (b) unst rce G is less a rapidly pro he fracture not occur at rest occurs b ess, K Ia , is t kinetic energ and 1b com ng force inco rgy, so, the d

able crack pro than or equa pagating cra initiates whe this point, b elow the re herefore less y created du pare materia rporates the ynamic defin

rrest (Anderso erial resistanc the materi f the structur tructure still e, after most material res ropagation; K ith quasi-sta etic energy, th gy release rat

n, 1995). e R . Similarl al resistance, e has a fallin contains kin of the avail istance, K IA . IA is a mat tic driving fo e Griffith-Ir e is [6]: ormation en r elasto-dyna (2) istance to c tion of the c e dynamic st (1)

In the cra cur ene ene dif pro cur ene wh and Co con wh pro spe For inte

y, if the g G etic able The erial rce win

d t  )( G

A k

 

, A is the fra ing equation

area, U is t crack propa

ergy mic

k done by ex own fracture

ternal forces , the govern

cture surface for Mode I

he elastic def gation unde

rack rack ress

, K I the ins istance ), whic ethods. propagation mic energy re

tress intensit the crack v ) is not equa be expresse

y factor and elocity and c l to the static d in the form

K ID is the an be measur stress intens :

tantaneous s h depends on periods, K I (t lease rate can

material res ed as a func ity factor. Th

(3.a)

Kv

)0( )( I

46