Why Direct Tension Test Specimens Break Flexing to the Side
Publication: Journal of Structural Engineering
Volume 119, Issue 4
Abstract
Contrary to the traditional view, unnotched direct tension test specimens of quasi‐brittle materials that exhibit post‐peak strain softening do not deform symmetrically. After passing the peak load, the equilibrium path bifurcates and the secondary postbifurcation branch represents flexing to the side. The bifurcation is shown to be analogous to Shanley's bifurcation in elastoplastic columns. According to the thermodynamic criterion of stable path, the flexing to one side must occur even if the geometry is perfect and if the straightening effect of the moment of the axial force about the centroid of the deflected cross section is taken into account. The lateral flexing favors failure of the specimen at midlength. The phenomenon (which is similar to the recently discovered behavior of notched tensile fracture specimens) is first illustrated using a simple model in which the specimen consists of two rigid bars of unequal lengths, joined by a strain‐softening link. It is shown that flexing to the side is retarded if the attachments to the loading machine exert a sufficient restraint against rotation. The analysis is then extended to a specimen consisting of two unloading elastic beams joined by a short strain‐softening segment, and similar conclusions are reached. The maximum load in the unnotched direct‐tension test gives the material strength limit, but the postpeak load‐deflection response cannot yield the strain‐softening material properties and energy‐absorption capability except when sophisticated stability analysis is made and the size of the strain‐softening zone is known a priori.
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References
1.
Bažant,Z. P. (1988). “Stable states and paths of structures with plasticity or damage.” J. Engrg. Mech., ASCE, 114(12), 2013–2034.
2.
Bažant, Z. P. (1989). “Stable states and stable paths of propagation of damage zones and interactive fractures.” Cracking and damage—strain localization and size effect, J. Mazars and Z. P. Bažant, eds., Elsevier, New York, 183–206.
3.
Bažant, Z. P., and Cedolin, L. (1991). Stability of structures—elastic, inelastic, fracture, and damage theories. Oxford University Press, New York, N.Y.
4.
Bažant, Z. P., and Tabbara, M. R. (1989). “Stable propagation of interacting crack systems and modeling of damage.” Trans., 10th Int. Conf. on Struct. Mech. in Reactor Tech. (SMiRT 10), A. H. Hadjian, ed., AASMiRT, Los Angeles, Calif., Vol. H, 85–93.
5.
Hill, R. (1958). “A general theory of uniqueness and stability in elastic‐plastic solids.” J. Mech. Phys. Solids, 6, 236–249.
6.
Hill, R. (1961). “Bifurcation and uniqueness in nonlinear mechanics of continua.” Problems of continuum mechanics, Society of Industrial and Applied Mathematics, Philadelphia, Pa., 155–164.
7.
Hordijk, D. A., Reinhardt, H. W., Cornelissen, H.A.W. (1987). “Fracture mechanics parameters of concrete from uniaxial tensile tests as influenced by specimen length.” Preprints, Conf. on Fracture of Concrete and Rock, S. P. Shah and S. E. Swartz, eds., SEM‐RILEM, Houston, Tex., 138–149.
8.
Hutchinson, J. W. (1974). “Plastic buckling.” Adv. Appl. Mech., 14, 67–144.
9.
Pijaudier‐Cabot, G., and Akrib, A. (1989). “Bifurcation et réponse postbifurcation de structures en béton.” Preprint, Colloquium GRECO, Rhéologie des Géomateriaux, GRECO, Paris, France (in French).
10.
Rots, J. G., and de Borst, R. (1987). “Analysis of mixed‐mode fracture in concrete.” J. Engrg. Mech., ASCE, 113(11), 1739–1758.
11.
Rots, J. G., and de Borst, R. (1989). “Analysis of concrete fracture in direct tension.” Int. J. Solids Struct., 25(12), 1381–1394.
12.
Shanley, F. R. (1947). “Inelastic column theory.” J. Aero Sci., 14(5), 261–268.
13.
van Mier, J. G. M. (1986). “Fracture of concrete under complex stresses.” Heron, Delft, The Netherlands, 31(3), 58.
14.
van Mier, J. G. M. (1989). “Fracture propagation in concrete under complex stress.” Fracture of Concrete and Rock; Proc., Int. Conf., SEM‐RILEM, Springer Verlag, New York, N.Y., 362–375.
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Copyright © 1993 American Society of Civil Engineers.
History
Received: Dec 23, 1991
Published online: Apr 1, 1993
Published in print: Apr 1993
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