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Notched strength of carbon fibre/epoxy composite laminates with a circular hole

Kerbfestigkeit von Kohlefaser/Epoxid-Verbund-Laminaton mit runden Öffnungen

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Abstract

This paper improves the two stress fracture criteria proposed by Whitney and Nuismer (known as the point stress criterion and the average stress criterion) to predict the strength of composite laminates with a circular hole. In the point stress criterion, it is assumed that the failure occurs when the stress over some distance (d 0) away from the notch is equal to or greater than the un-notched laminate strength. In the average stress criterion it is assumed that failure occurs when the average stress over some distance (a 0) ahead of the notch equals the unnotched laminate strength. Both stress fracture criteria are two parameter models based on the unnotched strength (σ 0) and a characteristic dimension (d 0 ora 0). A simple relation is used for the characteristic length to improve the accuracy while evaluating the notched strength of carbon/epoxy composite laminates. The analytical results are compared well with the existing test results of AS4-carbon/948 Al epoxy [0/90]4s and [0/ ± 45/90]2S composite laminates with various hole diameters and specimen widths.

Zusammenfassung

In diesem Artikel wird eine verbesserte Form der Bruchspannungskriterien von Whitney und Nuismer vorgestellt, die für die Berechnung der Spannungen in Verbundíaminaten verwendet wird, weiche eine runde Öffnung aufweisen. Der Ansatz mit einem lokalen spannungskriterium geht davon aus, daß ein Versagen des Werkstoffes dann auftritt, sobald die Spannung in einer bestimmmten Entfernungd 0 von der Kerbe die Festigkeit des ungekerbten Laminates übserschreitet. Der Ansatz des mittleren Spannungskriterium legt zugrunde, daß ein Materialversagen dann auftritt, wenn die mittlere Spannung in einer bestimmten Entfernunga 0 von der Einkerbung die Festigkeit des ungekerbten Laminates überschreitet. Beide Bruchspannungsansätze sind zwei-parametrische Berechnungsansätze basierend auf der Festigkeitσ 0 des kerbfreien Material und einer charakteristischen Länged 0 bzw.a 0. Eine relativ einfache Beziehung wird für die Bestimmung der charakteristischen Länge eingeführt, um die Berechnung der Kerbfestigkeit von Kohlefaser/Epoxid-Verbund-Laminaten zu verbessern. Die erhaltenen, analytischen Ergebnisse stimmen gut mit den verfügbaren Meßwerten von AS4-carbon/948 Al epoxy [0/90]4S and [0/± 45/90]2S Verbund-Laminaten unterschiedlicher Abmessungen überein.

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Abbreviations

a 0 :

characteristic length for the average stress criterion

c :

half-crack length

c p ,c k :

notch sensitivity parameters

d 0 :

characteristic length for the point stress criterion

D(≡2R):

hole diameter

E xx ,E yy ,G xy :

axial, transverse and shear moduli respectively

K 1 :

stress intensity factor

K Q,∞ :

asymptotic value of the stress intensity factor

K F ,K F1,K F2 :

fracture toughness parameters

K ∞ T ,K T :

stress concentration factors for infinite and finite width plates

m, m 1,m 2 :

fracture parameters

m p ,m k :

exponential parameters

M :

magnification factor

R :

hole radius

R 0 :

reference radius

W :

specimen width

x.y :

axial and transverse directions

ν xy :

Poisson’s ratio

ν yx :

ν xy E yy /E xx

Φ1 :

R/(R +d 0)

Φ2 :

R/(R +a 0)

Φ3 :

c/(c +d 0)

Φ4 :

c/(c +a 0)

σ 0 :

unnotched strength of laminate

σ y :

normal stress alongy-direction

σ ∞ N :

applied uniform stress alongy-direction

σ ∞ N ,σ N :

notched strength for infinite and finite width plates

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Authors and Affiliations

  1. Structural Engineering Group, Vikram Sarabhai Space Centre, 695022, Trivandrum, India

    P. K. Govindan Potti & B. Nageswara Rao

  2. Department of Mechanical Engineering, Institute of Technology, Banaras Hindu University, 221005, Varanasi, India

    V. K. Srivastava

Authors
  1. P. K. Govindan Potti
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  2. B. Nageswara Rao
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  3. V. K. Srivastava
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Govindan Potti, P.K., Nageswara Rao, B. & Srivastava, V.K. Notched strength of carbon fibre/epoxy composite laminates with a circular hole. Forsch Ing-Wes 65, 295–300 (1999). https://doi.org/10.1007/BF03035110

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  • DOI: https://doi.org/10.1007/BF03035110

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