Fast, accurate, and reliable detection of damage in aircraft composites by advanced synergistic infrared thermography and phased array techniques

This paper presents an advanced methodology for the detection of damage in aircraft composite materials based on the sensor fusion of two image-based non-destructive evaluation techniques. Both of the techniques, phased-array ultrasonics and infra-red thermography, are benchmarked on an aircraft-grade painted composite material skin panel with stringers. The sensors systems for carrying out the inspections have been developed and miniaturized for being integrated on a vortex-robotic platform inspector, in the framework of a larger research initiative, the Horizon-2020 ‘CompInnova’ project

Assessment of Fatigue Damage and Crack Propagation in Ceramic Matrix Composites by Infrared Thermography

The initiation and propagation of damage in SiC fiber-reinforced ceramic matrix composites under static and fatigue loads were assessed by infrared thermography (IRT). The proposed thermographic technique, operating in lock-in mode, enabled early prediction of the residual life of composites, and proved vital in the rapid determination of the materials’ fatigue limit requiring testing of a single specimen only. IRT was also utilized for quantification of crack growth in the materials under cyclic loads. The paper highlights the accuracy and versatility of IRT as a state-of-the art damage assessment tool for ceramic composites

A novel processing route for carbon nanotube reinforced glass-ceramic matrix composites

Conference on Smart Sensor Phenomena, Technology, Networks, and Systems Integration, San Diego, CA, MAR 09-10, 2015International audienceThe current study reports the establishment of a novel feasible way for processing glass-and ceramic-matrix composites reinforced with carbon nanotubes (CNTs). The technique is based on high shear compaction of glass/ceramic and CNT blends in the presence of polymeric binders for the production of flexible green bodies which are subsequently sintered and densified by spark plasma sintering. The method was successfully applied on a borosilicate glass/multi-wall CNT composite with final density identical to that of the full-dense ceramic. Preliminary non-destructive evaluation of dynamic mechanical properties such as Young's and shear modulus and Poisson's ratio by ultrasonics show that property improvement maximizes up to a certain CNT loading; after this threshold is exceeded, properties degrade with further loading increase

Nondestructive Damage Evaluation in Ceramic Matrix Composites for Aerospace Applications

Infrared thermography (IRT) and acoustic emission (AE) are the two major nondestructive methodologies for evaluating damage in ceramic matrix composites (CMCs) for aerospace applications. The two techniques are applied herein to assess and monitor damage formation and evolution in a SiC-fiber reinforced CMC loaded under cyclic and fatigue loading. The paper explains how IRT and AE can be used for the assessment of the material’s performance under fatigue. IRT and AE parameters are specifically used for the characterization of the complex damage mechanisms that occur during CMC fracture, and they enable the identification of the micromechanical processes that control material failure, mainly crack formation and propagation. Additionally, these nondestructive parameters help in early prediction of the residual life of the material and in establishing the fatigue limit of materials rapidly and accurately

Ensuring near-optimum homogeneity and densification levels in nanoreinforced ceramics

Conference on Smart Materials and Nondestructive Evaluation for Energy Systems 2016, Las Vegas, NV, MAR 21-23, 2016International audienceThe development of a new generation of high temperature ceramic materials for aerospace applications, reinforced at a scale closer to the molecular level and three orders of magnitude less than conventional fibrous reinforcements, by embedded carbon nanotubes, has recently emerged as a uniquely challenging scientific effort. The properties of such materials depend strongly on two main factors: i) the homogeneity of the dispersion of the hydrophobic medium throughout the ceramic volume and ii) the ultimate density of the resultant product after sintering of the green body at the high-temperatures and pressures required for ceramic consolidation. The present works reports the establishment of two independent experimental strategies which ensure achievement of near perfect levels of tube dispersion homogeneity and fully dense final products. The proposed methodologies are validated across non-destructive evaluation data of materials performance

Multifunctional Cement Mortars Enhanced with Graphene Nanoplatelets and Carbon Nanotubes

Recent findings have brought forward the potential of carbon nano-species, especially nanotubes and graphene, to impart exceptional multifunctional potential to cement, offering simultaneous enhancement of mechanical, fracture mechanical and electrical properties. While available knowledge on the topic is still limited, there is a complete absence of direct comparisons of the potential of the nano-species to improve strength and toughness and provide multifunctionality to the mortars. The study offers a comprehensive overview of these potentials, for mortars modified with pure graphene nanoplatelets and carbon nanotubes at consistent, directly comparable, concentrations up to 1.2 wt.%. Testing included flexure under pure bending moments, axial compression, electrical resistivity measurements and fracture tests under three point bending configuration; the latter were also independently assessed by acoustic emission. Differences in documented properties and optimal concentrations associated with improved mechanical performance were directly compared and rationalized in terms of nanospecies morphology. Dramatic, statistically consistent improvements in fracture behavior, up to 10-fold of control values, were documented for specific nanofiller concentrations, indicating an excellent potential of the material system for contemporary smart construction applications. An exceptionally favorable comparison of acoustic emission and fracture energy data confirmed that the non-destructive technique can independently assess the fracture performance of mortars with exceptional precision

Unstable SpO2 in preterm infants: The key role of reduced ventilation to perfusion ratio.

Peer reviewed: TrueAcknowledgements: The authors thank Dr A. Olszowka, Department of Physiology, University of Buffalo, New York, United States for providing his pulmonary gas exchange program.Introduction: Instability of peripheral oxyhemoglobin saturation (SpO2) in preterm infants is correlated with late disability and is poorly understood. We hypothesised that a reduced ventilation to perfusion ratio (VA/Q) is the key predisposing factor for SpO2 instability. Methods: We first used a mathematical model to compare the effects of reduced VA/Q or shunt on SaO2 stability (SaO2 and SpO2 are used for model and clinical studies respectively). Stability was inferred from the slope of the SaO2 vs. inspired oxygen pressure (P IO2) curve as it intersects the 21 kPa P IO2 line (breathing air). Then, in a tertiary neonatal intensive care unit, paired hourly readings of SpO2 and P IO2 were recorded over a 24 h period in week old extremely preterm infants. We noted SpO2 variability and used an algorithm to derive VA/Q and shunt from the paired SpO2 and P IO2 measurements. Results: Our model predicted that when VA/Q 8% fluctuation in SaO2 at 21 kPa P IO2. In contrast, when a 20% intrapulmonary shunt was included in the model, a 1% change in P IO2 results in 0.85) but only two infants had increased shunt at 1.1 (±0.5) weeks' postnatal age. Median (IQR) SpO2 fluctuation was 8 (7)%. The greatest SpO2 fluctuations were seen in infants with VA/Q < 0.52 (n = 10): SpO2 fluctuations ranged from 11%-17% at a constant P IO2 when VA/Q < 0.52. Two infants had reduced VA/Q and increased shunt (21% and 27%) which resolved into low VA/Q after 3-6 h. Discussion: Routine monitoring of P IO2 and SpO2 can be used to derive a hitherto elusive measure of VA/Q. Predisposition to SpO2 instability results from reduced VA/Q rather than increased intrapulmonary shunt in preterm infants with cardiorespiratory disease. SpO2 instability can be prevented by a small increase in P IO2

Multifunctional Cement Mortars Enhanced with Graphene Nanoplatelets and Carbon Nanotubes

Recent findings have brought forward the potential of carbon nano-species, especially nanotubes and graphene, to impart exceptional multifunctional potential to cement, offering simultaneous enhancement of mechanical, fracture mechanical and electrical properties. While available knowledge on the topic is still limited, there is a complete absence of direct comparisons of the potential of the nano-species to improve strength and toughness and provide multifunctionality to the mortars. The study offers a comprehensive overview of these potentials, for mortars modified with pure graphene nanoplatelets and carbon nanotubes at consistent, directly comparable, concentrations up to 1.2 wt.%. Testing included flexure under pure bending moments, axial compression, electrical resistivity measurements and fracture tests under three point bending configuration; the latter were also independently assessed by acoustic emission. Differences in documented properties and optimal concentrations associated with improved mechanical performance were directly compared and rationalized in terms of nanospecies morphology. Dramatic, statistically consistent improvements in fracture behavior, up to 10-fold of control values, were documented for specific nanofiller concentrations, indicating an excellent potential of the material system for contemporary smart construction applications. An exceptionally favorable comparison of acoustic emission and fracture energy data confirmed that the non-destructive technique can independently assess the fracture performance of mortars with exceptional precision

Unstable SpO2 in preterm infants: The key role of reduced ventilation to perfusion ratio.

Introduction: Instability of peripheral oxyhemoglobin saturation (SpO2) in preterm infants is correlated with late disability and is poorly understood. We hypothesised that a reduced ventilation to perfusion ratio (VA/Q) is the key predisposing factor for SpO2 instability. Methods: We first used a mathematical model to compare the effects of reduced VA/Q or shunt on SaO2 stability (SaO2 and SpO2 are used for model and clinical studies respectively). Stability was inferred from the slope of the SaO2 vs. inspired oxygen pressure (P IO2) curve as it intersects the 21 kPa P IO2 line (breathing air). Then, in a tertiary neonatal intensive care unit, paired hourly readings of SpO2 and P IO2 were recorded over a 24 h period in week old extremely preterm infants. We noted SpO2 variability and used an algorithm to derive VA/Q and shunt from the paired SpO2 and P IO2 measurements. Results: Our model predicted that when VA/Q 8% fluctuation in SaO2 at 21 kPa P IO2. In contrast, when a 20% intrapulmonary shunt was included in the model, a 1% change in P IO2 results in 0.85) but only two infants had increased shunt at 1.1 (±0.5) weeks' postnatal age. Median (IQR) SpO2 fluctuation was 8 (7)%. The greatest SpO2 fluctuations were seen in infants with VA/Q < 0.52 (n = 10): SpO2 fluctuations ranged from 11%-17% at a constant P IO2 when VA/Q < 0.52. Two infants had reduced VA/Q and increased shunt (21% and 27%) which resolved into low VA/Q after 3-6 h. Discussion: Routine monitoring of P IO2 and SpO2 can be used to derive a hitherto elusive measure of VA/Q. Predisposition to SpO2 instability results from reduced VA/Q rather than increased intrapulmonary shunt in preterm infants with cardiorespiratory disease. SpO2 instability can be prevented by a small increase in P IO2