EN 1007-5-2010 pdf download.Advanced technical ceramics – Ceramic composites – Methods of test for reinforcements – Part 5: Determination of distribution of tensile strength and of tensile strain to failure of filaments
within a multifilament tow at ambient temperature.
3.9
filament stress
ratio of the tensile force to the cross sectional area of aU unbroken filaments at stepj in the non-linear parts of the force-displacement curve
3.10
average filament rupture strain
statistical average rupture strain of the filaments in the tow for each test determined from the Weibull strain distribution parameters of the filaments
3.11
overall average filament rupture strain
arithmetic mean of the average filament rupture strains
3.12
average filament strength
0,-
statistical average strength of the filaments in the tow for each test determined from the Weibull strength distribution parameters of the filaments
3.13
overall average filament strength
arithmetic mean of the average filament strengths
3.14
compliances
3.14.1
initial total compliance
inverse slope of the linear part of the force-displacement curve
3.14.2
instantaneous total compliance
Cu
inverse slope of the secant at any point) in the non-linear part of the force-displacement curve
NOTE The slope Is taken from a line through any point of the force-displacement curve and the intersection point of the line of the initial total compliance with the abscissa (true origin).
3.14.3
load train compliance
ratio of the cross head displacement to the force, excluding any contribution of the test specimen to the displacement during the tensile test
3.14.4
compliance of the tow dow
instantaneous total compliance of the tow at maximum tensile force
4 Principle
A multitilament tow is loaded in tension. The test is performed at a constant displacement rate up to failure of all fibres. Force and cross-head displacement are measured and recorded simultaneously. When required, the longitudinal deformation is derived from the cross-head displacement using a compliance correction. From the force-displacement curve, the two-parameter Weibull distribution of the rupture strain and the distribution of the rupture strength of the filaments are obtained by sampling the non-linear parts of the curve at discrete intervals j, which correspond to an increasing number of failed filaments in the tow. The test duration is limited to reduce time dependent effects.
5 Significance and use
The measurement of strain directly on the tow is difficult, so it is usually achieved indirectly via a compliance measurement that includes contributions of the loading train, grips, tab materials. etc. When it is possible to measure the tow elongation directly (by using a suitable extensometer system) this correction is not needed, The calculation of the results in Clause 10 also applies in this case by setting the load train compliance equal to zero.
The evaluation method is based on an analysis of the non-linear increasing and decreasing parts of the force- displacement curve, which are caused by progressive filament failure during the test. The occurrence of these stages is promoted by a higher stiffness of the loading and gripping system. This method of evaluation Is only applicable when the force-displacement curve shows these non-linear parts.
The distribution of filament rupture strains does not depend on the number of filaments in the tow and is hence not affected by the number of filaments that are broken before the test. The determination of the filament strength distribution and of the elastic modulus necessitates knowtedge of the initial cross sectional area of the tow. Because the number of unbroken filaments within the tow prior to the test Is usually unknown, the values for the filament strength and for the elastic modulus necessarily represent lower bounds to these quantities. Also, the variation in filament diameter, which affects the strength values, is not accounted for.
6 Apparatus
6.1 Tensile testing equipment
The test machine shall be equipped with a system tor measuring tne torce appliei to me specimen and the displacement, or directly the tow elongation. Additionally, the machine shall be equipped with a system for measuring the crosshead displacement with accuracy better than 1 rim.
6.2 Load train
The grips shall align the test specimen with the direction of the force. Slippage of the test specimen in the grips shall be prevented as well as avoiding pre-damage due to gripping.
NOTE The use of a displacement transducer placed at the ends of the grips (see FIgure 1) should limit the contribution of different parts of the load train to the measured displacement. and hence should increase the accuracy.EN 1007-5-2010 pdf download.