Analysis of the effects of AFP singularities by multi-instrumented tests on plane and open-hole coupons
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Loïc MARQUET (FRANCE), Juan-Manuel GARCIA (FRANCE), Cédric HUCHETTE (FRANCE), Christian FAGIANO (FRANCE), Stephanie MIOT (FRANCE), Attilio CHIAPPINI (FRANCE), Alain RASSINEUXAbstract :
Automated Fiber Placement (AFP) offer new manufacturing capabilities extending the application of CFRP. However, it induces irregularities such as gaps and overlaps (respectively, the lack or the overlapping of tapes during the manufacturing). These irregularities are defined in this work as “singularities” as they are inherent to the AFP process and, in some cases to the parts’ design itself. Several authors have studied the effects of gaps and overlaps on the failure properties of CFRP [1,2] and on the microstructure geometry [3] of laminates. Since their effects on the failure scenario are still not completely understood, they are considered in this work mainly through experimental testing at the coupon-scale.
A test campaign including tensile and compression tests with monotonic and incremental level loadings is performed at ONERA with a multi-instrumented set-up. 16 plies quasi-isotropic plane and open-hole coupons following aeronautical industry stacking rules are manufactured and embed severe designs of rectangular and triangular shaped singularities positioned at different plies throughout the thickness. The kinematic fields on two faces of the specimen are monitored with two pair of cameras in stereo vision. The damage kinetic occurring inside the coupon is recorded by acoustic emissions sensors.
Ex-situ X-ray micro-tomography scanner (CT-scan) allows a description of the manufactured geometry and the damage state within the coupons. The objective of this multi-instrumented set up is to further understand the effects of singularities on the characteristic damage mechanisms up to failure.
At the macro scale, tensile and compression open-hole tests, show the minor effects of singularities versus the hole effect. On the opposite, plane tensile tests highlight the effects of singularities on mechanical properties; gaps tend to have a weakening effect while overlaps show a strengthening effect. For compression loading, the conclusions are less straightforward, since the loading conditions are not comparable for each singularity design. For instance, the coupon with the most severe gaps configuration has the strongest failure properties.
Thanks to the complementarity of the multi-instrumented set-up we are able to deeper understand the damage kinetic in tension loading. The processing of CT-scan observations shows a high matrix cracking density in regions close to gaps and overlaps, within the core of the coupons, see figure attached. Acoustic emission combined with processing of displacement fields obtained by a specific digital images correlation method (Deepflow) able to observe the influence of singularities on the matrix transverse cracking evolution. For compression loading, the instrumentation helps to understand the effective local loading state at the coupon-scale and underlines the necessity to integrate a numerical simulation to the analysis.
A test campaign including tensile and compression tests with monotonic and incremental level loadings is performed at ONERA with a multi-instrumented set-up. 16 plies quasi-isotropic plane and open-hole coupons following aeronautical industry stacking rules are manufactured and embed severe designs of rectangular and triangular shaped singularities positioned at different plies throughout the thickness. The kinematic fields on two faces of the specimen are monitored with two pair of cameras in stereo vision. The damage kinetic occurring inside the coupon is recorded by acoustic emissions sensors.
Ex-situ X-ray micro-tomography scanner (CT-scan) allows a description of the manufactured geometry and the damage state within the coupons. The objective of this multi-instrumented set up is to further understand the effects of singularities on the characteristic damage mechanisms up to failure.
At the macro scale, tensile and compression open-hole tests, show the minor effects of singularities versus the hole effect. On the opposite, plane tensile tests highlight the effects of singularities on mechanical properties; gaps tend to have a weakening effect while overlaps show a strengthening effect. For compression loading, the conclusions are less straightforward, since the loading conditions are not comparable for each singularity design. For instance, the coupon with the most severe gaps configuration has the strongest failure properties.
Thanks to the complementarity of the multi-instrumented set-up we are able to deeper understand the damage kinetic in tension loading. The processing of CT-scan observations shows a high matrix cracking density in regions close to gaps and overlaps, within the core of the coupons, see figure attached. Acoustic emission combined with processing of displacement fields obtained by a specific digital images correlation method (Deepflow) able to observe the influence of singularities on the matrix transverse cracking evolution. For compression loading, the instrumentation helps to understand the effective local loading state at the coupon-scale and underlines the necessity to integrate a numerical simulation to the analysis.