1. Introduction
The presence of a notch in a structure induces a stress concentration
which may initiate a crack leading to a catastrophic failure
in brittle materials. Among the various approaches which have
been proposed to assess crack initiation in the vicinity of a notch
[1], we focus on the volume-based strain energy density (SED)
method developed by Lazzarin and Zambardi [2]. This criterion
states that brittle failure occurs when the mean value of the strain
energy density over a given volume surrounding the tip of the
notch reaches a critical value. It is shortly outlined in the case of
a V-notch in a homogeneous isotropic material. The suggested
shape of the control volume is a cylinder which base is a circular
sector (with an area SðR; aÞ depending on the radius R and the
opening angle a) centered on the tip of the notch (Fig. 1).
Assuming plane elasticity conditions, the strain energy in the
control volume is:
WðR; aÞ ¼ 1
2
b
ZZ
SðR;aÞ
reds ð1Þ
where b is the specimen thickness and r, e are respectively the
stress and strain fields.
The averaged strain energy density is given by:
WðR; aÞ ¼ WðR; aÞ
bSðR; aÞ
ð2Þ
The SED criterion predicts crack initiation under tensile failure
if:
WðR; aÞ ¼ Wc ð3Þ
with Wc ¼ ðrc Þ2
2E where rc is the tensile strength and E is the Young’s
modulus. The critical point is the determination of the radius R
which was initially considered as a material property [2]. If an
asymptotic analysis is used [3], one obtains for a mode I loading:
WðR; aÞ ¼ 1
E
eðaÞ K21
R2ð1kÞ
ð4Þ
where k ð0:5 6 k 6 1Þ is the characteristic exponent of the singularity
generated by the sharp notch, eðaÞ is a dimensionless parameter,
K1 is the generalized stress intensity factor.
Combining (3) and (4) provides the radius R:
R ¼ 2eðaÞ Kc
1
rc
2 " #1
2ð1kÞ
ð5Þ
which is dependent on the fracture properties ðrc ; Kc
1
Þ and the notch
opening angle a. Experimental data can thus be used to estimate R
but another solution is to introduce an expression of the critical
value Kc
1 in terms of the strength and toughness of the notched
material [3]. Using the coupled criterion formulation proposed by
Leguillon [4] gives:
Kc
1
¼ E
ð1 m2ÞCðaÞ Gc
1k
ðrcÞ2k1 ð6Þ
where C(a) is a dimensionless scaling coefficient and m is the Poisson’s
ratio. Combining (5) and (6) leads to:
R ¼ 2
eðaÞ 1
2ð1kÞ
CðaÞ2 Lc ð7Þ
where Lc ¼ E
1m2
Gc
ðrc Þ2 defines a characteristic fracture length
1. IntroductionThe presence of a notch in a structure induces a stress concentrationwhich may initiate a crack leading to a catastrophic failurein brittle materials. Among the various approaches which havebeen proposed to assess crack initiation in the vicinity of a notch[1], we focus on the volume-based strain energy density (SED)method developed by Lazzarin and Zambardi [2]. This criterionstates that brittle failure occurs when the mean value of the strainenergy density over a given volume surrounding the tip of thenotch reaches a critical value. It is shortly outlined in the case ofa V-notch in a homogeneous isotropic material. The suggestedshape of the control volume is a cylinder which base is a circularsector (with an area SðR; aÞ depending on the radius R and theopening angle a) centered on the tip of the notch (Fig. 1).Assuming plane elasticity conditions, the strain energy in thecontrol volume is:WðR; aÞ ¼ 12bZZSðR;aÞreds ð1Þwhere b is the specimen thickness and r, e are respectively thestress and strain fields.The averaged strain energy density is given by:WðR; aÞ ¼ WðR; aÞbSðR; aÞð2ÞThe SED criterion predicts crack initiation under tensile failureif:WðR; aÞ ¼ Wc ð3Þwith Wc ¼ ðrc Þ22E where rc is the tensile strength and E is the Young’smodulus. The critical point is the determination of the radius Rwhich was initially considered as a material property [2]. If anasymptotic analysis is used [3], one obtains for a mode I loading:WðR; aÞ ¼ 1EeðaÞ K21R2ð1kÞð4Þwhere k ð0:5 6 k 6 1Þ is the characteristic exponent of the singularitygenerated by the sharp notch, eðaÞ is a dimensionless parameter,K1 is the generalized stress intensity factor.Combining (3) and (4) provides the radius R:R ¼ 2eðaÞ Kc1rc 2 " #12ð1kÞð5Þwhich is dependent on the fracture properties ðrc ; Kc1Þ and the notchopening angle a. Experimental data can thus be used to estimate Rbut another solution is to introduce an expression of the criticalvalue Kc1 in terms of the strength and toughness of the notchedmaterial [3]. Using the coupled criterion formulation proposed byLeguillon [4] gives:Kc1¼ Eð1 m2ÞCðaÞ Gc 1kðrcÞ2k1 ð6Þwhere C(a) is a dimensionless scaling coefficient and m is the Poisson’sratio. Combining (5) and (6) leads to:R ¼ 2eðaÞ 12ð1kÞCðaÞ2 Lc ð7Þwhere Lc ¼ E1m2Gcðrc Þ2 defines a characteristic fracture length
การแปล กรุณารอสักครู่..