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Normal and shear stress gages and rosettes for orthotropic composites

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Abstract

Stress gages, plane-shear gages, and three-element strain rosettes have long been used in experimental-mechanics investigations on isotropic materials. This paper generalizes these concepts for applications to fiber-reinforced composite materials. Also included for the first time are data-reduction equations whichexplicitly incorporate strain-gage transverse sensitivity.

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Abbreviations

C :

stress/measured strain constant; see eqs (15), (23), and (26)

E :

Young's modulus

F :

gage factor

G :

shear modulus

K :

transverse-sensitivity factor of gage element

Q ij :

plane-stress reduced elastic stiffnesses

ΔR/R o :

relative change in gage electrical resistance

ε:

actual normal strain

ε′:

measured apparent normal strain

ν:

Poisson's ratio (=negative of the transverse strain divided by the longitudinal strain when loaded uniaxially in longitudinal direction)

γ xy :

shear strain associated with grid lines in x and y directions

σ:

normal stress

ϕ:

angular orientation of a gage element from a reference axis

a, t :

axial and transverse with respect to gage-element axis

i :

associated with manufacturer's gage calibration on isotropic material

max :

maximum

ss :

shear associated with directions x and y

u :

uniaxial-loading case

x,y :

associated with orthogonal reference directions (in fiber composite, x is the fiber direction)

xx, yy :

associated with primary normal-stress stiffness

xy :

associated with secondary (Poisson) normal-stress stiffness

1,2:

associated with gages elements 1 and 2

3, 3n :

associated with gage element 3 and direction normal to it

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Authors and Affiliations

  1. School of Aerospace, Mechanical and Nuclear Engineering, University of Oklahoma, 73019, Norman, OK

    Charles W. Bert (SEM Fellow) is Perkinson Professor of Engineering)

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  1. Charles W. Bert
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Bert, C.W. Normal and shear stress gages and rosettes for orthotropic composites. Experimental Mechanics 25, 288–293 (1985). https://doi.org/10.1007/BF02325099

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  • DOI: https://doi.org/10.1007/BF02325099

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