Foreign Object Impact Research Articles

An Improved Impact Source Locating System Using FBG Rosette Array.

For structures vulnerable to foreign object impact damages, it would be desirable to detect and locate any occurrence of such impacts. This can be achieved by monitoring the stress waves generated by an impact together with certain source localization algorithms. Being small, electromagnetic influence immune and durable, Fiber Bragg grating (FBG) sensors are advantageous for this task. One drawback of FBGs for this purpose is their uneven directional sensitivity, which limits its localization ability to within 50° on either side of the fiber axis. Beyond this range, the signal is too weak and masked by noises and the location errors increase abruptly. Two approaches have been tested on a 0.8 m × 0.8 m × 6 mm plate for possible improvement on the system accuracy: firstly, an interrogation scheme with stronger light source intensity and steeper edge filter is employed to enhance the signal-to-noise ratio and system sensitivity; secondly, rosettes with two orthogonal FBGs are cascaded together to replace single FBGs to alleviate the directional sensitivity problem. It was found that a four-fold increase in signal to noise ratio contributed by stronger light source does improve the location accuracy, but only marginally. For the rosette approach, the relative positions of the Bragg wavelength of the FBGs and the light source spectrum are crucial to accuracy. Three different wavelength configurations have been tested and the reasons for their success or failure are discussed. It was shown that with an optimal wavelength configuration, the rosette array can virtually extend the good location accuracy to all over the plate.

The Influence of TBC Aging on Crack Propagation Due to Foreign Object Impact.

While a plane is maneuvering before take-off and landing, some solid particles (e.g. sand, dust, soil) may get into the engine with air. A vast majority of them are stopped by the compressor blades, but the smaller ones can get into a hot part of the engine and cause erosion. A pneumatic laboratory work station was built in order to investigate the impact of foreign object damage (FOD) particles with a diameter of 4 mm. Cylindrical samples with a diameter of 30 mm were used, each having a thermal barrier coating (TBC) deposited by the air plasma spray (APS) method with the application of yttria-stabilized zirconia (YSZ). Sample aging was performed for four ranges: 48, 89, 185, and 353 h at the temperature of 1000 °C. After aging, samples were subjected to impacts made with different energies. Various damage images were captured depending on the aging time and impact velocity. Numerical studies led to the determination of how the incidence angle of a foreign object and the blade temperature affected the number of elements that became damaged during impact. It was found that impacts perpendicular to the surface were the most dangerous, while heating the blade to the operating temperature resulted in a 27% decrease in the number of elements damaged during impact when compared to the cold blade.

Impact Localization of Thin Plate Structures Using Pzt-Array Based Passive Wave Method

Impact of foreign objects is one of the main reasons for the damage of thin plate structures, resulting in property losses or unexpected accidents. Therefore, a rapid and effective impact localization of thin plate structures is of great value. In this paper, a localization method is proposed based on the passive wave method, aiming at locating the impact quickly and accurately. First, a square PZT array composed of 4 PZT sensors was designed, and a hyperbolic localization algorithm was derived according to time-different of arrival (TDoA) for different sensors in the array. Then, Matlab calculation software was used to perform DB wavelet decomposition on impact signals, the time delay was calculated by Lamb wave of A0 mode in D5 detail signals, and the velocity of A0 mode wave was determined by the dispersion curve for 1 mm thick aluminum plate. Finally, the impact point was located to experimentally verify the effectiveness of the proposed localization method. Experimental results show that the hyperbolic positioning algorithm based on TDoA can accurately identify impact locations, and wavelet decomposition can effectively identify single mode Lamb waves. The proposed method has the characteristics of fastness and accuracy, which is suitable for single object impact localization on thin plate structures.

Wave-based impact localization on laminated composite plates using a coarse network of sensors

This article demonstrates a methodology for the detection of foreign object impact locations on laminated composite plates using a low number of sensors. The proposed approach exploits the wave-dominated transient response of the target structure and addresses the challenges induced by the non-uniform wave propagation due to the anisotropy of composite plates on the impact localization. Captured sensor signals are processed and their frequency content is identified. Semi-analytical wave dispersion models and time-domain spectral finite element impact models encompassing the effects of laminate anisotropy on wave dispersion characteristics are employed to extract the wave velocity from their frequency content. The method for localizing the impact site is formulated as an optimization problem and involves signal correlation from different sensors, refinement of the candidate locations, and finally accurate estimation of the impact site. Numerical and experimental validations of the developed method are presented for low-velocity impacts on glass/epoxy laminated plates.

Transient Analysis for a Twin Spool Rotor with Squeeze-Film Dampers Considering Blade Loss

The transient, nonlinear vibration of a twin spool rotor assembly in the situation of blade loss should be accurately examined. To relate the macroscopic vibration of the rotor with blade damage, a power-function based model is proposed to express the mass unbalance force to the rotor during the blade loss, which is different from the traditional loading using the step function. With this function the characteristics of damage growth with time is exhibited for both foreign object damage and high fatigues of engine blades. The governing equation of transient rotordynamics considering nonlinear squeeze-film damping force is derived and solved numerically in fault operations using different blade loss parameters. Various cases of different blade loss durations have been simulated with the proposed function. It is demonstrated through results that the present model of loading is suitable for transient analysis for the damaged rotor due to blade losses by foreign object impact and high-cycle fatigues.

Fracture mechanism maps for thermal barrier coatings subjected to single foreign object impact

To further understand the erosion mechanism of the electron beam physical vapor deposited thermal barrier coatings, the failure mechanism diagrams with different parameters were established by finite element simulations. The effects of various parameters on foreign object erosion were discussed. The location and type of coating cracks under different conditions were predicted. It was found that the possibility of crack nucleation increases with the increase of the particle velocity, particle radius and impact angle. Compared to the structural and material parameters of thermal barrier coatings, the erosion particle parameters (particle velocity, particle radius and impact angle) have a greater effect on the coating failure. All of these results give corresponding suggestions and advices for process optimization of thermal barrier coatings.

Comparison of impact behaviour of glass, carbon and Dyneema composites

Lightweight fibre-reinforced polymer composites are currently being applied extensively in the design of transport structures to replace conventional metallic solutions, and also in structures that are exposed to the risk of foreign object impact. Therefore, an experimental study was undertaken to assess and compare the low- and high-velocity impact behaviour of S-2 glass®, HTA carbon and ultra-high-molecular-weight polyethylene (Dyneema®) composites. Three different impact test methods were applied: Charpy pendulum impact tests, drop-weight impact tests and ballistic impact tests with a gas gun. The results with the focus on penetration energy are compared in terms of correlation between the three test methods and in terms of weight-specific material performance. While the S-2 glass® fibre showed the best performance of the epoxy-based composites, the PUR-based Dyneema® HB26 panels proved the best penetration resistance in this study.

Fatigue life and defect tolerance calculation for specimens with foreign object impact and scratch damage

In this paper, a new method is proposed to calculate the fatigue life and defect tolerance for a 30CrMnSiA steel specimen with foreign object impact damage and scratch damage. First, the processes of foreign object impact and scratch are simulated. Then, the Lemaitre’s plasticity damage model is adopted to calculate the initial damage field arising from the impact process and scratch process. Second, the Chaudonneret’s damage model is applied to calculate the fatigue damage for the specimen with a defect under multiaxial fatigue loading. Then, the FE implementation of the damage mechanics model is presented in the platform of ANSYS, in which the coupling effect between the stress and damage fields is considered. Finally, this proposed method is applied to fatigue life and defect tolerance calculation for the 30CrMnSiA steel specimen with an impact defect and a scratch defect. The experiments were conducted to evaluate the approach mentioned above.

Analysis of Oil Debris in an Aero Gas Turbine Engine

Oil debris count is an important health monitoring parameter in aero gas turbine engine. Present paper deals with the oil debris analysis collected from the bearing houses and gear box of a military gas turbine engine. Due to relative motion between stationary parts, wearing-out has taken place in turbine bearing house. Improper assembly or dimensional inaccuracies found to be the root cause of high debris generation. For wearing-out of the drive shaft in gear box, lapses in assembly procedure and improper tolerances are found to be responsible. Though high ‘g’ maneuvers of the aircraft, hard landings, missile launch and bird hit or foreign object impact can lead to such high debris in the oil circuit, utmost care needs to be taken during assembly.

Analysis of the Damage of Boiler Bottom Slope Pipe in Steam Power Plant

Bottom slope pipe on boiler system in one of steam turbine power plant had been damaged. The damage was dent on the outside of pipe and was suspected as a result from foreign object impact from outside pipe. From chemical composition examination and hardness test, it showed that nothing wrong with the selection of the pipe. From visual inspection, there is no other factor such as corrosion or deposit formed inside the pipe was found. Analysis of cause of damage in the pipe then further conducted by observing microstructure and hardness value on the area which experience damage. Simulation on mechanical and thermal analysis had been conducted to determine what and origin of foreign object which impacted on pipe and the temperature when it was happened. From the observation, of microstructure and hardness test showed that pipe had been experience plastic deformation on temperature under recrystallization temperature. Simulation results also confirmed that the initial assumption on cause of pipe damage from foreign object, which is small size slag that felt from very high location so that caused high speed impact on pipe. Thermal analysis result also supporting the suspicion that slag impact on pipe was occurred in temperature under recrystallization of pipe material.

Identification of impact force acting on composite laminated plates using the radiated sound measured with microphones

Foreign object impact events are serious threats to composite laminates because impact damage leads to significant degradation of the mechanical properties of the structure. Identification of the location and force history of the impact that was applied to the structure can provide useful information for assessing the structural integrity. This study proposes a method for identifying impact forces acting on CFRP (carbon fiber reinforced plastic) laminated plates on the basis of the sound radiated from the impacted structure. Identification of the impact location and force history is performed using the sound pressure measured with microphones. To devise a method for identifying the impact location from the difference in the arrival times of the sound wave detected with the microphones, the propagation path of the sound wave from the impacted point to the sensor is examined. For the identification of the force history, an experimentally constructed transfer matrix is employed to relate the force history to the corresponding sound pressure. To verify the validity of the proposed method, impact tests are conducted by using a CFRP cross-ply laminate as the specimen, and an impulse hammer as the impactor. The experimental results confirm the validity of the present method for identifying the impact location from the arrival time of the sound wave detected with the microphones. Moreover, the results of force history identification show the feasibility of identifying the force history accurately from the measured sound pressure using the experimental transfer matrix.

Finite Element Analysis of Laminated Composite Skewed Hypar Shell Roof Under Oblique Impact with Friction

Impact of foreign objects on laminated composite has become a great concern despite its other advantages. Hypar (hyperbolic-paraboloid), a preferred shell roof geometry is frequently subjectedto such impacts. In most of the practical situations such impacts are oblique. Present study investigates dynamic behaviour of a simply supported composite hypar shell roofs under oblique impact, considering modified Hertzian contact law, for different impact velocities and impact angles allowing for anisotropic friction. Time dependent equations are solved using Newmark's time integration algorithm. Time histories of contact force at point of impact and that of displacement are presented to extract significant engineering conclusions. There are also proposals of practical parameters for designing such shells through static simplification of the problems.

Deformation Response of Titanium Alloy under Static and Dynamic Loading

Response of a material under dynamic loading is different as compared to static loading. Dynamic material properties are therefore necessary for assessment of structural integrity and safety. Gas turbine aero engine frontal components like fan and compressors are critical and prone for foreign object impact as these components are exposed directly to the environment. Design of aircraft engine components like fan and compressor are critical and it is mandatory to design such components to withstand high impact loads. In view of this high strain rate test of Ti-6Al-4V alloy has been carried out in strain rate range of 1000 s-1 to 4000 s-1 using Split Hopkinson Bar (SHB). Force equilibrium analysis for each test is carried out to confirm the validity of the test results. Quasi-static test was also carried out for comparison with high strain rate test. From the tests, flow behavior of Ti-6Al-4V alloy at high strain rate is obtained. It is observed that the material have positive strain rate sensitivity and it fails by fracture under high strain rate compressive loading.

Low-velocity impact response analysis of composite pressure vessel considering stiffness change due to cylinder stress

To accurately analyse the transient response and damage of pressurized vessels subjected to a drop impact or foreign object impact, we must consider the change in stiffness due to pre-stress. The pre-stress condition induces a phenomenon where thin plates with in-plane pre-stress show different stiffness during out-of-plane deflections compared to the original plate without the in-plane pre-stress. Because the cylindrical wall of a pressurized vessel is under in-plane pre-stress induced by the vessel’s internal pressure, we must consider the ‘change in stiffness’ to accurately analyse the impact response and damage. In this study, we investigated the low-velocity impact response of a composite laminated cylinder wall of a pressure vessel with high internal pressure. The shear deformation theory of a doubly curved shell and von Karman’s large deflection theory, as well as a newly proposed strain–displacement relation including initial strain terms to consider the stiffness change induced by cylinder stress due to internal pressure, were used to develop a geometrically nonlinear finite-element program. Numerical results that were calculated for the cylinder stress showed larger contact force and smaller deflection. By comparing strain values, a simple superposition of strain value calculated without considering cylinder stress and initial cylinder strain value showed 10–20% more strain than that accurately calculated with considering the stiffness change due to cylinder stress.

Continuum damage mechanics-based approach to the fatigue life prediction for 7050-T7451 aluminum alloy with impact pit

A continuum damage mechanics-based approach is proposed to predict the fatigue life of 7050-T7451 aluminum alloy that has undergone foreign object impact damage. Lemaitre’s plasticity damage model is adopted to evaluate the damage field arisen from impact. Then Chaudonneret’s damage model is applied to the fatigue damage accumulation caused by cyclic loading. The numerical dynamic analysis simulating the foreign object impact process is conducted to obtain the plastic strain history and the residual stress field. Fatigue damage evolution is implemented by the finite element method via coupling operations on the damage field and the stress field. The fatigue test for specimens with an impact pit is conducted to validate the aforementioned approach. The predicted life and the site of crack initiation are in accordance with the test results. Finally, the effects of impact plastic damage, residual stress, impact pit depth, and radius on the fatigue life are investigated.

Impact properties of glass fiber/epoxy composites at cryogenic environment

Abstract Glass fiber/epoxy polymer (GFRP) composites are widely used in the aerospace engineering industry due to their high specific strength to weight ratio with non-corrosive properties, however they are very sensitive to foreign object impact. This study aims at investigating the impact response of GFRP composites at different temperature environments, which are encountered in their service at high attitude and low earth orbit (LEO) conditions. 18 GFRP samples were fabricated by vacuum infusion process and 9 of them were post-cured at 353 K for 3 h to ensure that a complete chemical reaction inside the samples was achieved. Low velocity drop weight test was performed for the samples prepared and then stored at room temperature (295 K), dry ice temperature (199 K) and liquid nitrogen temperature (100 K) conditions. The apparent damages and their size were visually examined and measured. Impact parameters such as impact load, deflection and energy absorption of each damage type were also analyzed. Besides, the post-curing effect was also studied to verify its significance to the impact properties of composites. Experimental results showed that GFRP composites at cryogenic condition exhibited smaller apparent damage and were stiffer as compared with other cases. However, they demonstrated relatively poor energy absorbability at low temperature condition. It was also found that post-curing could reduce the apparent damage and increase the energy absorption of GFRP composites.

Low Velocity Impact Behaviors of a Laminated Glass

Dynamic behaviors of a laminated glass subjected to foreign object impact are studied by the use of the developed finite element program. A finite element simulation based on a higher-order beam finite element and a PVB interlayer model is applied to compute the dynamic responses of laminated glass panel. In this analysis, the glass plies and PVB interlayer are modeled as linear elastic. The results such as the histories of contact force and deflection, and the distribution for strains, stresses through the beam thickness during impact are obtained. The impact behaviors of laminated glass panel are compared with those of the monolithic glass of the same total thickness. It shows that PVB interlayer can be prevented inner glass ply of LG beam from damage by reducing the stress to zero. Specially, stress distribution through the thickness except PVB interlayer in impact analysis shows nearly linear unlike that of static analysis in spite of its discontinuity of the short time shear modulus of PVB in a laminated glass.

New possibilities of using spin rigs to provide gas turbine engine strength reliability

The main tasks of using spin rigs for carrying out certification, engineering and technological tests of gas turbine engine parts and assemblies are formulated. Specific design features of spin rigs are described in the paper. The main characteristics of the spin rigs used at CIAM are presented. The peculiarities of carrying out different tests using spin rigs and the main requirements for rigs are discussed. Examples of using spin rigs for carrying out tests are given. Examples of using the rigs are given, among them are tests intended to confirm the rotor load capacity or technological hardening of the rotor material; equivalent-cyclic tests to confirm the rotor life; investigation of the vibration properties of rotating parts (optimization of structural damping of vibrations and specifying high-cycle fatigue of rotating blades, etc.); tests carried out to confirm the containment of rotor fragments in the engine casing and to determine the rotor integrity under the impact of bird or other foreign objects sucked in the engine gas-air flow duct. The necessity of combining spin rig tests with calculations and physical investigations is shown. The main directions of updating spin rigs are considered. In particular, the necessity of developing rigs for different tests of engine fans with high bypass ratios; perfecting rigs and testing procedures for high-cycle fatigue investigations of rotating blades; producing the equipment for thermal cycling tests of rotor parts, especially parts made of composite or ceramic materials; investigation of vibrations in the conditions of rotor-stator contact; improvement of hardware and methods.

Photovoltaic Modules Destruction Analysis

In this paper we present the analysis of the causes that caused the destruction of photovoltaic modules cover glass in the group of modules randomly located in the photovoltaic field. Operator of photovoltaic system excluded the possibility of damage of these modules by impact of foreign objects because of their location in the photovoltaic field and because of no records of hail or similar events in this area. Damage of the cover glass in analyzed module appears to be adequate of safety glass cracking - uneven web of cracks in the glass with six central location with a different structure cracking. In the three of these areas is possible to find the area with the browning of the surface on the photovoltaic cells main contacts. This article also includes summarization of method which is possible to use for analyses of photovoltaic modules state.

Damage characterization and numerical modeling of titanium matrix composites subjected to low-velocity impact for landing gear application

Titanium matrix composites (TMCs) is considered as a candidate material for landing gear structures of the aircraft, which requires the damage tolerant consideration. In order to investigate the damage behavior of SiC-fiber/titanium matrix composites subjected to foreign object impact, low-velocity impact experiments are conducted. Finite element modeling to simulate the damage behavior of TMCs is developed considering the plastic deformation and the damages. Numerical results of mechanical response and damage behavior are compared with experimental results. It is shown that the developed modeling can capture the impact damage of TMCs. In the last part of the present study, a prototype of TMC landing gear structure is fabricated. Impact damage behavior and residual compressive strength are evaluated, and the results are compared with numerical simulation.