ACCURACY ESTIMATION OF ELASTICITY MODULI EVALUATED BY FOUR-POINT BENDING

ACCURACY ESTIMATION OF ELASTICITY MODULI EVALUATED BY FOUR-POINT BENDING

journal article - other

en

The present paper deals with practical applicability of four-point bending in determination of elasticity moduli. In [1] and [2], a theory was derived for evaluation of elasticity moduli by four point bending, namely for materials showing different moduli in tension and in compression, and for thin layers (e.g. plasmatic coatings), respectively. The limitations for reasonable exploitation of this method lie in the inaccuracy of results. As it can be expected, and as it was already mentioned in [2], the influence of input quantities inaccuracy on the results error can be very substantial. This is, in particular, the case of thin layers; since the measured plasmatic layer represents a small part of the specimen cross – section (usually less than 10%), the influence of the layer parameters (modulus of elasticity, thickness) on the resulting strain is relatively low. In an inverse problem, consequently, small changes in measured strains or thickness can result in large deviations in the determined moduli of elasticity for these layers. These non-linear dependences are analysed in the paper and, as a consequence, general rules for practical use of this method are formulated.

The present paper deals with practical applicability of four-point bending in determination of elasticity moduli. In [1] and [2], a theory was derived for evaluation of elasticity moduli by four point bending, namely for materials showing different moduli in tension and in compression, and for thin layers (e.g. plasmatic coatings), respectively. The limitations for reasonable exploitation of this method lie in the inaccuracy of results. As it can be expected, and as it was already mentioned in [2], the influence of input quantities inaccuracy on the results error can be very substantial. This is, in particular, the case of thin layers; since the measured plasmatic layer represents a small part of the specimen cross – section (usually less than 10%), the influence of the layer parameters (modulus of elasticity, thickness) on the resulting strain is relatively low. In an inverse problem, consequently, small changes in measured strains or thickness can result in large deviations in the determined moduli of elasticity for these layers. These non-linear dependences are analysed in the paper and, as a consequence, general rules for practical use of this method are formulated.

The present paper deals with practical applicability of four-point bending in determination of elasticity moduli. In [1] and [2], a theory was derived for evaluation of elasticity moduli by four point bending, namely for materials showing different moduli in tension and in compression, and for thin layers (e.g. plasmatic coatings), respectively. The limitations for reasonable exploitation of this method lie in the inaccuracy of results. As it can be expected, and as it was already mentioned in [2], the influence of input quantities inaccuracy on the results error can be very substantial. This is, in particular, the case of thin layers; since the measured plasmatic layer represents a small part of the specimen cross – section (usually less than 10%), the influence of the layer parameters (modulus of elasticity, thickness) on the resulting strain is relatively low. In an inverse problem, consequently, small changes in measured strains or thickness can result in large deviations in the determined moduli of elasticity for these layers. These non-linear dependences are analysed in the paper and, as a consequence, general rules for practical use of this method are formulated.

Modul pružnosti, čtyřbodový ohyb

Modulus of elasticity, four-point bending

2004

01.12.2004

1210-2717

11

6

12