Effect of thermal cycling aging on tensile damage initiation in 3D woven OMC for aeroengine applications
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Salvador ORENES BALACIART (FRANCE), Yannick PANNIER (FRANCE), David MELLIER (FRANCE), Marco GIGLIOTTI (FRANCE)Abstract :
Introduction
Three-Dimensional Woven Organic Matrix composites are increasingly used as elements of structural parts close to aircraft engines and in aero-engine fan blades. These materials are therefore requested to operate in high-performance ranges subjected to mechanical solicitations at different temperatures and exposed to cold/hot thermal cycling. Not much research has been carried out concerning damage onset in such materials. Moreover, there is almost no research concerning the effect of thermal cycling induced ageing and degradation on damage onset of such materials [1]. The present work investigates the damage onset induced by a preliminary thermal cycling between 120°C and -55°C using Acoustic Emission (AE) and X-Ray micro-Computed Tomography (XRmCT). AE is used to detect first damage and while XRmCT is used to obtain 3D volume scan to visualize damage mechanisms. Damage propagation up to 1000 cycles has been characterized in detail in the 3D woven meso-structure and quantitatively analyzed in terms of cracked surface by image techniques. Finally, the effect of thermal cycling degradation on damage onset is investigated in an in-situ tensile test.
Material and Methods
3D interlock IM7/PR520 composite samples made for research purpose by Resin Transfer Molding were provided by Safran Group.
Dogbone specimens were exposed to thermal cycling between 120ºC and -55ºC (Fig.1). In contrast with previous works where triangular cycles are set [2, 3], here a 2h plateau is imposed at 120°C. The objective is to examine the fatigue damage mechanisms induced by thermo oxidation phenomena at high temperature and stresses at low temperature. AE tracking is used to monitor damage during thermal cycling and XRmCT is used to characterize crack surface evolution. In a second step, a tensile loading is applied in situ under XRmCT scanner to assess the influence of this conditioning on damage onset.
Results
The results show that the onset of thermal cycling pre-damage starts as matrix cracking inside weft yarns at the surfaces of the specimens; furthermore AE tracking reveals that onset of damage always occurs at sub-zero temperatures. Interface between yarn and matrix and intra-warp yarns are the following damage mechanisms. As the number of cycles increases, the number of onset sites at surface multiplies, as well as damage initiation at the core starts to take place (Fig.2). XRmCT monitoring allows characterization of the damage evolution, from small surface cracks to matrix-yarn debonding. Scanning of relatively large section of the specimens (≈ 2 RVE) allows for robust damage characterization in the woven pattern.
Finally, the effect of thermal cycling has shown an effect on the damage onset investigated through an in-situ tensile test with respect to a virgin state.
Three-Dimensional Woven Organic Matrix composites are increasingly used as elements of structural parts close to aircraft engines and in aero-engine fan blades. These materials are therefore requested to operate in high-performance ranges subjected to mechanical solicitations at different temperatures and exposed to cold/hot thermal cycling. Not much research has been carried out concerning damage onset in such materials. Moreover, there is almost no research concerning the effect of thermal cycling induced ageing and degradation on damage onset of such materials [1]. The present work investigates the damage onset induced by a preliminary thermal cycling between 120°C and -55°C using Acoustic Emission (AE) and X-Ray micro-Computed Tomography (XRmCT). AE is used to detect first damage and while XRmCT is used to obtain 3D volume scan to visualize damage mechanisms. Damage propagation up to 1000 cycles has been characterized in detail in the 3D woven meso-structure and quantitatively analyzed in terms of cracked surface by image techniques. Finally, the effect of thermal cycling degradation on damage onset is investigated in an in-situ tensile test.
Material and Methods
3D interlock IM7/PR520 composite samples made for research purpose by Resin Transfer Molding were provided by Safran Group.
Dogbone specimens were exposed to thermal cycling between 120ºC and -55ºC (Fig.1). In contrast with previous works where triangular cycles are set [2, 3], here a 2h plateau is imposed at 120°C. The objective is to examine the fatigue damage mechanisms induced by thermo oxidation phenomena at high temperature and stresses at low temperature. AE tracking is used to monitor damage during thermal cycling and XRmCT is used to characterize crack surface evolution. In a second step, a tensile loading is applied in situ under XRmCT scanner to assess the influence of this conditioning on damage onset.
Results
The results show that the onset of thermal cycling pre-damage starts as matrix cracking inside weft yarns at the surfaces of the specimens; furthermore AE tracking reveals that onset of damage always occurs at sub-zero temperatures. Interface between yarn and matrix and intra-warp yarns are the following damage mechanisms. As the number of cycles increases, the number of onset sites at surface multiplies, as well as damage initiation at the core starts to take place (Fig.2). XRmCT monitoring allows characterization of the damage evolution, from small surface cracks to matrix-yarn debonding. Scanning of relatively large section of the specimens (≈ 2 RVE) allows for robust damage characterization in the woven pattern.
Finally, the effect of thermal cycling has shown an effect on the damage onset investigated through an in-situ tensile test with respect to a virgin state.