Long-term Performance Deterioration Research Articles

An Integrated Monitoring, Diagnostics, and Prognostics System for Aero-Engines under Long-Term Performance Deterioration

In the field of aircraft engine diagnostics, many advanced algorithms have been proposed over the last few years. However, there is still wide room for improvement, especially in the development of more integrated and complete engine health management systems to detect, identify, and forecast complex faults in a short time. Furthermore, it is necessary to ensure that these systems preserve their capabilities over time despite engine deterioration. This paper addresses these necessities by proposing an integrated system that considers the joint operation of feature extraction, anomaly detection, fault identification, and prognostic algorithms for engines with long operation times. To effectively reveal the actual engine condition, light adaptive degraded engine models are computed along with different health indicators that are used as inputs to train and test recognition and prediction models. The system is developed and evaluated using a specialized NASA platform which provides data from a turbofan engine fleet simultaneously experiencing long-term performance deterioration and faults. Contrary to other compared solutions, our results show that the proposed system is robust against the effects of engine deterioration, maintaining its level of detection, recognition, and prediction accuracy over a total engine service life. The low computational cost algorithms has generally fast performance in all stages, making the system suitable for online applications.

Long-term performance deterioration models for semi-rigid asphalt pavement in cold region

As the demand for the semi-rigid asphalt pavement reconstruction and maintenance technologies is increasing in the seasonal cold regions, the pavement performance deterioration models are essential for the success of the reconstruction and maintenance projects. This study is carried out to develop the deterioration models based on the preliminary investigation results of typical successful maintenances. All critical technical indexes concerning the asphalt pavement maintenance were studied. By combining the engineering practices, a long-term performance database of the semi-rigid asphalt pavement was established through a large amount of survey data, and the related environmental parameters. Based on the database achieved, the deterioration models of the semi-rigid asphalt pavement performances were built via the statistical regression method. It is concluded that the proposed deterioration models were useful and practical for the establishment of the maintenance decision of the semi-rigid asphalt pavements.

Optimization of the drilling Parameters for GFRP Composite using Taguchi Technique

The surface roughness and the delamination are important difficulties in any drilling operation of (GFRP) composite materials. Both two elements cause structural integrity reduction and poor assembly as well as the potential for long-term performance deterioration. In this research, the optimization of drilling parameters using Taguchi technique, to obtain minimum both surface roughness (Ra) and the delamination factor (df). In addition, ANOVA uses to analyze the data obtained from the experiments and determine the optimal parameters in the drilling of GFRP composite materials. The results revealed that the delamination factor (df) increases with the increase of drilling speed (2250rpm-2750rpm) and increases with the increase of the feed rate (100mm/min to 125mm/min). Increasing the drilling speed and reducing feed rate can reduce the delamination factor (df) and the use of high feed rate and high spindle speed can be increasing the delamination factor (df) within the limits of specified speed and feed rates. The feed rate is the more influential factor on delamination than the other parameters. The results for very low feed rate i.e. 25mm/min and high drilling speed 2750 rpm show a clear decrease in surface roughness (Ra). Feed rate and drilling speed are the more influential factors on surface roughness (Ra) than the other parameters.

Data Analytics for Performance Monitoring of Gas Turbine Engine

Performance analysis of a low power rating and partially loaded industrial gas turbine engine (GTE) was carried out by using a model-free data analytic approach. By adopting an efficient input selection method, several performance indices (PI) are proposed to quantify the performance of the GTE. These indices are extracted using engine operating data related to power output and parameters related to fuel consumption, and validated with engine performance monitoring measurements for a three year period corresponding to one time between overhaul intervals. The dependency of the PIs on ambient temperature has been studied by using linear and polynomial fitting curves. Then novel methods are introduced for analysis of short-term and long-term performance deterioration arising from compressor fouling and structural degradation respectively. The results have clearly shown the ability of the proposed PIs to detect short-term compressor fouling as well as long-term performance deterioration, which is directly relevant to the Prognostics and Health Management of gas turbine engine.

Drilling of polymer matrix composites: A review

This article addresses the effects of drilling parameters on the machinability parameters in drilling polymeric composite materials. Drilling parameters include: feed, speed, drill wear, drill geometry, drilling with special tools, and composite materials parameters. The machinability parameters include: thrust force, torque, residual strength, surface roughness, and mechanical and thermal damages of the composite materials. Delamination associated with drilling processes can often be the limiting factor for composite materials in structural applications. It results in reducing the structural strength, poor assembly tolerance and, hence, it has the potential for long-term performance deterioration. Therefore, special interest will be given for reporting factors affecting the delamination onset, delamination mechanisms, measurements, assessments, and delamination-free techniques in drilling fiber-reinforced composites.

The effect of vibratory drilling on hole quality in polymeric composites

The anisotropy of fiber-reinforced plastics (FRP) affects the chip formation and thrust force during drilling. Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced plastics, which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce good quality holes with high efficiency by conventional drilling method. This research concerning drilling of polymeric composites aims to establish a technology that would ensure minimum defects and longer tool life. Specifically, the authors conceived a new drilling method that imparts a low-frequency, high amplitude vibration to the workpiece in the feed direction during drilling. Using high-speed steel (HSS) drill, a series of vibratory drilling and conventional drilling experiments were conducted on glass fiber-reinforced plastics composites to assess thrust force, flank wear and delamination factor. In addition, the process-status during vibratory drilling was also assessed by monitoring acoustic emission from the workpiece. From the drilling experiments, it was found that vibratory drilling method is a promising machining technique that uses the regeneration effect to produce axial chatter, facilitating chip breaking and reduction in thrust force.

Delamination in drilling GFR-thermoset composites

Delamination is a major problem associated with drilling fiber-reinforced composite materials that, in addition to reducing the structural integrity of the material, also results in poor assembly tolerance and has the potential for long-term performance deterioration. Delamination-free in drilling different fiber reinforced thermoset composites is the main objective of the present paper. Therefore the influence of drilling and material variables on thrust force, torque and delamination of GFRP composites was investigated experimentally. Drilling variables are cutting speed and feed. Material variable include matrix type, filler and fiber shape. Drilling process was carried out on cross-winding/polyester, continuous-winding with filler/polyester, chopped/polyester, woven/polyester and woven/epoxy composites. A simple inexpensive accurate technique was developed to measure delamination size. The results show that the presence of sand filler in continuous-winding composites not only raised the values of cutting forces and push-out delamination but also increased their values with increasing cutting speed. In contrast, increasing the cutting speed in drilling cross-winding, woven and chopped composites reduces the push-out delamination as a result of decreasing the thrust force. The thrust forces in drilling continuous-winding composite are more than three orders of magnitude higher than those in the cross-winding composites. Chopped composites have lower push-out delamination than those made from woven fibers. For the same fiber shape, the peel-up and push-out delaminations of woven/epoxy composite are lower than that for woven/polyester composites. Delamination, chipping and spalling damage mechanisms were observed in drilling chopped and continuous-winding composites. In drilling woven composites the delamination was observed at different edge position angles due to the presence of the braids that made by the interlacing of two orthogonal directions of fibers tows (warp and fill). Delamination-free in drilling cross-winding composites was achieved using variable feed technique.

DELAMINATION IN DRILLING GFR-THERMOSET COMPOSITES

Delamination is a major problem associated with drilling fiber-reinforced composite materials that, in addition to reducing the structural integrity of the material, also results in poor assembly tolerance and has the potential for long-term performance deterioration. Delamination-free in drilling different fiber reinforced thermoset composites are the main objective of the present paper. Therefore the influence of drilling and material variables on thrust force, torque and delamination of GFRP composites was investigated experimentally. Drilling variables are cutting speed and feed. Material variable include matrix type, filler and fiber shape. Drilling process was carried out on cross-winding/polyester, continuous-winding with filler/polyester, chopped/polyester, woven/ polyester and woven/epoxy composites. A simple inexpensive accurate technique was developed to measure delamination size. The results show that the presence of sand filler in continuous-winding composites not only raised the values of cutting forces and push-out delamination but also increased their values with increasing cutting speed. In contrast, increasing the cutting speed in drilling cross-winding, woven and chopped composites reduces the push-out delamination as a result of decreasing the thrust force. The thrust forces in drilling continuous-winding composite are more than three orders of magnitude higher than those in the cross-winding composites. Chopped composites have lower push-out delamination than that made from woven fibers. For the same fiber shape, the peel-up and push-out delaminations of woven/epoxy composite are lower than that for woven/polyester composites. Delamination, chipping and spalling damage mechanisms were observed in drilling chopped and continuous-winding composites. In drilling woven composites the delamination was observed at different edge position angles due to the presence of the braids that made by the interlacing of two orthogonal directions of fibers tows (warp and fill). Delamination-free in drilling cross-winding composites was achieved using variable feed technique.

Study on vibration drilling of fiber reinforced plastics with hybrid variation parameters method

Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced plastics (FRPs), which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce precise quality holes with high efficiency by conventional drilling method. In this paper, a new vibration drilling technology is presented using a hybrid variation parameters method, based on the model for predicting critical thrust forces and the model for predicting thrust and torque during vibration drilling of FRPs. From the drilling experiments, it was found that both precise quality holes and high efficiency could be obtained by this new drilling method.

Evaluation of anisotropic thermal conductivity for unidirectional FRP in laser machining

Due to the significant thermal anisotropy and the high-ablation temperature of carbon fiber, thermal damage can be produced during the thermal processing of carbon fiber-reinforced plastics by laser. It leads to poor assembly tolerance and long-term performance deterioration. The current study investigates the grooving of unidirectional Carbon/Epoxy in several representative directions relative to the fiber axis. Two methods, the Eigenvalue Method and the Isotherm Method, have been used to evaluate the general anisotropic thermal conductivities from the principal thermal conductivities. A finite-difference analysis, incorporating the Conductivity Ellipsoid Model due to Jaeger and the developed thermal conductivity models, is adopted to determine the extent of heat affected zone (HAZ). Simulations using either thermal conductivity model show a reasonable agreement with experimental results, i.e. the Eigenvalue Method and Isotherm Method for determining the thermal conductivity in generic direction are equally effective in the subsequent prediction of HAZ of an unidirectional FRP.

Principle Component Analysis Based Control Charts with Memory Effect for Process Monitoring

In this research, the combination of the principal component analysis (PCA) model and the traditional techniques with memory effect is developed for detecting the process influenced by a small or a moderate shift in one or more process variables. The traditional techniques, like the exponentially weighted moving average and the cumulative sum, use additional information from the past history of the process for keeping the memory effect of the process behavior trend. On the other hand, PCA can find a set of combination variables which can describe the key variations and trends for the operating data. This integrated method is particularly important for long-term performance deterioration, such as product quality degradation, because gradual small shifts are more difficult to diagnose than a sudden failure of equipment. The complementarity of these methods not only leads to some cross-fertilization between various techniques but also results in a better model. The comparison between the properties of the di...

Mechanical model for predicting thrust and torque in vibration drilling fibre-reinforced composite materials

Delamination is a dramatic problem associated with drilling fibre-reinforced composite materials (FRCMs), which, in addition to reducing the structural integrity of the material, also results in poor assembly tolerance and has the potential for long-term performance deterioration. The key to solving the problem lies in reducing the thrust force of drilling. In this paper, a theoretical analysis for predicting mean values of thrust and torque in vibration drilling FRCMs is presented. The model is based on mechanics of vibration cutting analysis and the continuous distributions of thrust and torque along the lip and the chisel edge of a twist drill. The result of a simulation study has shown a very good agreement between the theoretical predictions and the experimental evidence. On the same cutting conditions, the thrust and the torque by the vibration drilling method are reduced by 20–30 percent, compared with conventional drilling.

The extent of laser-induced thermal damage of UD and crossply composite laminates

Composite materials exhibit poor quality cut surfaces due to spalled fibres, fuzzing, and delamination when routed by conventional tools. Laser beam cutting offers an ideal means for the cutting of fibre composite materials, being a non-contact and virtually force-free manufacturing method. However, in the shaping operation of composite materials after curing, thermal damage associated with laser energy can be produced. It leads to poor assembly tolerance and long-term performance deterioration. In the current investigations, 3-dimensional anisotropic heat conduction models based on moving point heat source for thermal analysis are presented to predict heat affected zone (HAZ). Also, the conductivity models allow to consider the anisotropic heat conductivity for unidirectional (UD) and [0/90] laminates. Taking the immersing heat source and Mirror Image Method into account would further improve the prediction of HAZ. Extensive experiments were conducted on composite materials to examine HAZ, and compared with experimental results. The analytical results show a good agreement with experiments.

THE EFFECTS OF CRYOGENIC SURROUNDINGS ON THERMAL-INDUCED DAMAGE IN LASER GROOVING OF FIBER-REINFORCED PLASTIC

The traditional cutting of fiber-reinforced plastics causes serious concern of tool wear. The merits of narrow cuts and flexible path of lasers lead to the application of the shaping operation of composite material after curing. However, laser-induced thermal damage is often produced. It leads to poor assembly tolerance and long-term performance deterioration, The current study derives the concept of laser machining in a cryogenic environment. The anisotropic heat affected zone (HAZ) associated with cryogenic parameters is experimentally and analytically investigated for both principal-axis and non-principal-axis grooving in the example of unidirectional Carbon/Epoxy laminates. In principal-axis grooving, an analytical model based on a moving point heat source with a Mirror Image Method and immersed heat source can illustrate the effect of cryogenic surrounding on HAZ, while Finite Difference Method (FDM) is applied for prediction in the case of nonprincipal-axis grooving. The results reveal that the extent of the HAZ can be reduced by the proposed use of a cryogenic environment in laser machining.

Prediction of Extent of Heat Affected Zone in Laser Grooving of Unidirectional Fiber-Reinforced Plastics

Laser has been widely used in various industrial applications including machining. However, in shaping operation of composite material after curing, thermal damage associated with laser energy can be produced. It leads to poor assembly tolerance and long-term performance deterioration. The current research investigates the anisotropic formation of the heat affected zone (HAZ) in unidirectional fiber-reinforced plastics induced by laser grooving. Preliminary analytical and experimental analysis reveal that the laser energy per unit length and fiber orientation-dependent thermal conductivity primarliy determine the induced thermal damage. The extent of HAZ is estimated by the isotherm of the matrix char temperature. Heat conduction is maximum along the fibers, and the HAZ shape is thus affected by the beam scanning direction relative to fiber orientation. The study investigates the grooving of laminated unidirectional carbon/epoxy, which demonstrates clear thermal damage in 90 degree (i.e., perpendicular grooving), 60 degree, 30 degree, and 0 degree (i.e., parallel grooving) relative to the fiber axis. A theoretical analysis based on moving point heat source is adopted to determine the extent of thermal damage in correlation with process parameters and material properties. Mirror Image Method is used for specimen of finite thickness. Considerations of temperature-dependence of thermal conductivity and the emmerged heat source further improve the prediction of HAZ. While HAZ in grooving along the principal material axes can be solved analytically, conductivity ellipsoid and finite difference can calculate the extent of HAZ induced by grooving in any direction relative to fiber axis.

The anisotropic heat-affected zone in the laser grooving of fiber-reinforced composite material

A heat-affected zone is frequently associated with the laser processing of materials. In the shaping of composite material after curing, thermal damage is found, such as matrix recession, matrix decomposition, and delamination, which lead to poor assembly tolerance and long-term performance deterioration. The current study analyzes the peculiar growth of the heat-affected zone due to laser energy and the anisotropy of heat conductivity from the anisotropic arrangement of the fiber reinforcement in the composite material. It further applies the concept that the cut quality can be improved by reducing the resulting temperature of the workpiece, which leads to laser machining at low temperature. The paper investigates the cutting of unidirectional laminated carbon/epoxy composite perpendicular to and parallel to the fiber axis, using a cool nitrogen jet to reduce thermal damage. A theoretical analysis based on moving-point heat-source theory is adopted to determine the extent of thermal damage in correlation with process parameters and material properties. The analytical solution is modified by the ‘mirror image method’ for a specimen of finite thickness. The range of the heat-affected zone is estimated by the isotherm of the matrix char temperature. Heat conduction is maximum along the carbon fibers, the heat-affected zone shape thus being affected by the beam scanning direction relative to the fiber orientation.

Delamination During Drilling in Composite Laminates

Delamination is the major concern during drilling of composite laminates. Delamination, in addition to reducing the structural integrity of the laminate, also results in poor assembly tolerance and has the potential for long-term performance deterioration. Drilling-induced delamination occurs both at the entrance and at the exit planes. This paper presents an analysis of delamination during drilling. The analysis uses a fracture mechanics approach in which the opening-mode delamination fracture toughness, a material parameter, is used with a plate model of the laminate. The analysis predicts an optimal thrust force (defined as the minimum force above which delamination is initiated) as a function of drilled hole depth. Good agreement is achieved with data obtained from drilling carbon fiber-epoxy laminates. An advantage of the model is that it can predict varying degrees of delamination for other materials, such as glass fiber-epoxy, and for hybrid composites. In addition, the optimal thrust force for no delamination can be used to control a drilling machine with thrust force feedback for maximizing productivity.