Foreign Object Damage Research Articles

Modeling of the Superficial Laser Shock Peening Treatment Process: Application on a Titanium Aircraft Turbine Engine Blade

This paper presents a numerical simulation of the Laser Shock Peening (LSP) process using Finite Element Method (FEM). The majority of the controlling parameters of the process have been taken into account. The LSP loading has been characterized by using a repetitive time Gaussian increment pressure applied uniformly at the impacted zone. The used behavior law of the treated material is supposed Johnson Cook elastic-viscous-plastic coupled with damage. The proposed model leads to obtain the surface modifications (i) the in-depth residual stresses profile, (ii) the induced plastic strains profile, (iii) the geometrical surface modification of the impacted zone and (iv) the superficial damage which can be induced in few cases, where the operating conditions are not well chosen and optimized. An aeronautical application of LSP has been carried out on aircraft turbine engine blade made by Ti-6Al-4V super alloy. This mechanical treatment is applied in order to increase the durability of titanium fan blades and decrease their sensitivity to foreign object damage (FOD). The resulting surface compressive residual stress significantly improves the high-cycle-fatigue properties of the component and greatly increases resistance to blade failure. Finally, we studied the feasibility of the influence of LSP treatment on the phenomenon of crack propagation by introducing a superficial crack defect on the edge of the studied blade structure. This is physically consistent and leads to optimize the operating conditions in order to limit the damage risks.

A study on low velocity impact damage evaluation and repair technique of small aircraft composite structure

Composite structures are very prone to damage at fairly modest levels of impact energy due to foreign object damages. A repair technique using external patch is recognized as an effective method to recover the damaged structures during service life. This work is focusing on the impact damage evaluation and the external patch repair techniques of the aircraft composite structure. The impact damages of composite laminates of the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate are simulated by the drop-weight type impact test equipment. The damaged specimens are repaired using the external patch repair method after removing the damaged area. The compressive strength test and analysis results of the repaired impact damaged specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, the strength recovery capability after repairing is investigated.

Crack propagation analysis of mechanically damaged compressor blades subjected to high cycle fatigue

This paper presents results of experimental crack propagation analysis of damaged compressor blades of the helicopter engine, subjected to high cycle fatigue. The blades used in investigations were preliminary defected to simulate the foreign object damage. The blades during experiment were entered into transverse vibration. The crack propagation process was conducted in resonance condition. During fatigue investigations the crack length and amplitude of the blade tip displacement were monitored. The fatigue beach marks were not well visible on the fracture. For better determine of crack front shape in the early stage of fatigue fracture, a few blades were vibrated only to the first crack detection. Next the blades were statically tensioned and ruptured with use the testing machine. During performing of an experiment, different schemes of fatigue fracture of the blades were observed. The main result of presented investigation is the crack growth plot obtained for the blade including defects similar to foreign object damage. The attention of this work is also devoted to methodical side of experimental crack propagation analysis of the blade subjected to high cycle fatigue.

Effect of laser peening on fatigue performance in 300M steel

This study investigated and quantified the ability of laser peening to extend fatigue life and mitigate common fatigue crack nucleation mechanisms including foreign object damage and stress corrosion cracking in high strength, 300M steel. Residual stress was measured and fatigue tests were completed for as-machined, shot peened and laser peened coupons tested under a variety of conditions including in a corrosive environment and with simulated foreign object damage. The results are compared to available reference data studying the application of another emerging surface treatment, low plasticity burnishing, to the same material (300M steel) and in similar coupons. Laser peening resulted in large stress-life improvements in each condition, with a 54% increase in fatigue strength in an air environment for laser peened coupons at a lifetime of one million cycles. Additional fatigue testing in the 300M program showed that laser peening mitigated fatigue strength losses and improved the lifetimes (relative to as-machined, air environment) for coupons subject to either a corrosive environment or simulated FOD. Performance of laser peened coupons under all conditions proved to be better than reference data for coupons treated with shot peening or low plasticity burnishing.

Failure analysis on tread throw of the tire of B737-800 airplane

This paper provides an analysis of tread throw of B737-800 airplane tire. The plane experienced tire tread throw during takeoff. Laboratory observation shows that there exist numerous dense beach marks around one shoulder area of the tire. These beach marks shows that the repair exposed cords area around tire shoulder is the origin of tread separation of the incident tire. It is believed that the poor adhesion of the repair exposed cords area caused fatigue accumulative damage to develop into a tread separation. The structure form of the main landing gear of B737-800 airplane leads to unbalanced loadings on the double-tire (wheel) of the main landing gear, this gave a promotion to tread throw of the tire. For this reason, repair limits for damages at tire shoulder should be controlled more strictly for tires of B737-800 airplane. A large deep foreign object damage (FOD) cut found on the center tread rib is ruled out to be the cause of the tire tread throw according to the sequencing crack method called T-junction procedure in wreckage analysis. Tire FOD cut simulation test was carried out to confirm this viewpoint about FOD cut.

The post-repair performance of Ti-6Al-4V after foreign object damage

During an aircraft's life, it will experience a variety of Foreign Object Damage (F.O.D.) strikes, some of which involve critical components in engines and undercarriage. The principal repair method for F.O.D. impacts is to grind away the visible surface damage, as long as this grind-out does not exceed limits on acceptable depth. However, F.O.D. also creates damage which may extend below the visible impact, and may therefore remain after the grind-out repair. This paper describes research which explores the extent to which this subsurface remnant damage might affect future in-service performance. It involved producing Ti-6Al-4V fatigue testing specimens which had contained identical or near identical damage and which are then to be subjected to grind-out repair to various depths. This approach allows the effect of any subsurface metallurgical damage or residual stresses to be assessed. The paper also describes the key features of the impact damage created using the standardised spherical impactors adopted, and the production of the fatigue specimens for fatigue testing to evaluate the performance of the as-damaged conditions with that of the various repair conditions to highlight the effect of the FOD on fatigue life

軟体衝突によるCFRPの損傷挙動

Carbon fiber reinforced plastics (CFRP) are important materials in the aerospace field. An aircraft may suffer from foreign object damage (FOD) during operation. The most critical and frequent FOD events are bird strikes. To increase the usage of CFRP as a structural material in airplanes, it is necessary to be satisfied with the data on its impact resistance and to clarify the damage mechanism of CFRP in case of bird strike. In this study, a soft body sphere was used, as a model for a bird. The sphere struck three types of CFRP plates fixed at cantilevered, and the effects of the impact energy on the damage behavior of the plates were investigated. The relationship of strain and stress distribution and the damage process of CFRP were investigated through finite element analysis of the impact of the sphere.

Investigation on Design for a 500 W Wind Turbine Composite Blade Considering Impact Damage

Recently wind energy has been alternatively used as a renewable energy resource instead of the mostly used fossil fuels due to their increasing scarcity and environmental issues. This work is to propose a structural design and analysis procedure for development of a 500 W class small wind turbine system which will be applicable to domestic use at a relatively low speed region like Korea. Structural analysis including load case study and stress, deformation, buckling, vibration and fatigue estimation was performed. In addition, the blade should be safe from the impact damage due to FOD (foreign object damage) including bird strikes. MSC Dytran was used to analyze the bird strike phenomenon on the blade, and the applied method, Arbitrary Lagrangian–Eulerian, was evaluated by comparison with the previous study results. Finally, the structural test was carried out and its test results were compared with the estimated results for evaluation of the designed structure.

J044081 自己治癒能力を有した長繊維強化セラミックスの強度特性([J04408]知的材料・構造システム(8))

Advanced self-healing ceramic which has the new function combined with continuous fiber reinforcement and self-healing has been developed to overcome the foreign object damage problem. In the present study, the prototype sample was prepared by employing alumina fiber and alumina and silicon carbide powders as matrix and healing agent. The prepared sample exhibited the alumina fiber pull-out induced by the prior fracture of the silicon carbide interlayer. Also it was found that the mechanical properties of silicon carbide interlayer and fiber/matrix interface were kept even if the sample was suffered with the heat treatment that simulated self-healing.

Development of GUI Type On-Line Condition Monitoring Program for a Turboprop Engine Using Labview

Recently, an aero gas turbine health monitoring system has been developed for precaution and maintenance action against faults or performance degradations of the advanced propulsion system which occurs in severe environments such as high altitude, foreign object damage particles, hot and heavy rain and snowy atmospheric conditions. However to establish this health monitoring system, the online condition monitoring program is firstly required, and the program must monitor the engine performance trend through comparison between measured engine performance data and base performance results calculated by base engine performance model.

Characterisation of foreign object damage (FOD) and early fatigue crack growth in laser shock peened Ti–6Al–4V aerofoil specimens

Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at the leading edge using a laboratory gas gun at 200 m/s, head-on; and at 250 m/s, at an angle of 45°. The specimens were then subjected to 4-point bend fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and early crack growth due to FOD and subsequent fatigue growth were examined in detail. The results were compared between the two impact conditions; and with those from samples without LSP treatment as well as those impacted with spherical projectiles. The results seem to suggest that LSP has improved the crack growth resistance post FOD. Delayed onset of crack initiation was observed in LSPed samples compared to those without LSP under similar loading conditions. Damage features depend on the geometry of the projectile, the impact angle as well as the impact velocity.

항공기 복합재 라미네이트의 충격 손상 부위 유지 보수 후 강도 복원 평가

Development of a small scale aircraft has been carried out for the BASA(Bilateral Aviation Safety Agreement) program in Korea. This aircraft adopted all the composite structures for environmental friendly by low fuel consumption due to its lightness behavior. However the composite structure has s disadvantage which is very weak against impact due to foreign object damages. Therefore the aim of this study is focusing on the damage evaluation and repair techniques of the aircraft composite structure. The damages of composite laminates including the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate were simulated by a drop weight type impact test equipment and the damaged specimen were repaired using the external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.

Design Overview of a Three Kilowatt Recuperated Ceramic Turboshaft Engine

A three kilowatt turboshaft engine with a ceramic recuperator and turbine has been designed for small unmanned air vehicle (UAV) propulsion and portable power generation. Compared with internal combustion (IC) engines, gas turbines offer superior reliability, engine life, noise and vibration characteristics, and compatibility with military fuels. However, the efficiency of miniature gas turbines must be improved substantially, without severely compromising weight and cost, if they are to compete effectively with small IC engines for long-endurance UAV propulsion. This paper presents a design overview and supporting analytical results for an engine that could meet this goal. The system architecture was chosen to accommodate the limitations of mature, cost-effective ceramic materials: silicon nitride for the turbine rotors and toughened mullite for the heat exchanger and turbine stators. An engine with a cycle pressure ratio below 2:1, a multistage turbine, and a highly effective recuperator is shown to have numerous advantages in this context. A key benefit is a very low water vapor-induced surface recession rate for silicon nitride, due to an extremely low partial pressure of water in the combustion products. Others include reduced sensitivity to internal flaws, creep, and foreign object damage; an output shaft speed low enough for grease-lubricated bearings; and the potential viability of a novel premixed heat-recirculating combustor.

Mitigation of Fretting Fatigue Damage in Blade and Disk Pressure Faces With Low Plasticity Burnishing

Low plasticity burnishing (LPB) is now established as a surface enhancement technology capable of introducing through-thickness compressive residual stresses in the edges of gas turbine engine blades and vanes to mitigate foreign object damage (FOD). The “fatigue design diagram” (FDD) method has been described and demonstrated to determine the depth and magnitude of compression required to achieve the optimum high cycle fatigue strength, and to mitigate a given depth of damage characterized by the fatigue stress concentration factor, kf. LPB surface treatment technology and the FDD method have been combined to successfully mitigate a wide variety of surface damage ranging from FOD to corrosion pits in titanium and steel gas turbine engine compressor and fan components. LPB mitigation of fretting-induced damage in Ti–6Al–4V in laboratory samples has now been extended to fan and compressor components. LPB tooling technology recently developed to allow the processing of the pressure faces of fan and compressor blade dovetails and mating disk slots is described. Fretting-induced microcracks that form at the pressure face edge of bedding on both the blade dovetail and the dovetail disk slots in Ti-6-4 compressor components can now be arrested by the introduction of deep stable compression in conventional computer numerical control (CNC) machine tools during manufacture or overhaul. The compressive residual stress field design method employing the FDD approach developed at Lambda Technologies is described in application to mitigate fretting damage. The depth and magnitude of compression and the fatigue and damage tolerance achieved are presented. It was found that microcracks as deep as 0.030in.(0.75mm) large enough to be readily detected by current nondestructive inspection (NDI) technology can be fully arrested by LPB. The depth of compression achieved could allow NDI screening followed by LPB processing of critical components to reliably restore fatigue performance and extend component life.

Synchrotron Strain Mapping of the Residual Strain Distribution around Foreign Object Damage in Laser Shock Peened Ti-6AL-4V Alloy

The current study investigates the effect of foreign object damage (FOD) on the pre-existing compressive residual stress field associated with laser shock peening (LSP) and its evolution upon combined LCF/HCF cycling. FOD was introduced onto an aerofoil-shaped specimen that had been previously LSP treated through ballistic impacts at angles of 0° and 45° to the leading edge. It is shown that the FOD notch created by 45° impact was asymmetric in shape and smaller in depth compared to that created at 0° impact. Significant through thickness compression was introduced parallel to the leading edge as a result of the LSP process. The residual strain distribution was mapped around the FOD notch by synchrotron X-ray radiation. The results show predominantly compressive stresses ahead of the notch, being greater for the 0 compared to 45 impact. No significant stress relaxation was observed after a combined (1000 HCF cycles superimposed on 1 LCF cycle) cycle.

Characterization of foreign object damage (FOD) and early fatigue crack growth in laser shock peened Ti-6AL-4V aerofoil specimens

Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage.In this study, a typical aerofoil specimen of Ti-6Al-4V alloy was used. The leading edge of the specimen is representative of a generic aerofoil geometry. The specimens were treated by laser shock peening (LSP) to generate protective residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at 250 m/s head-on at the leading edge using a laboratory gas gun. The specimens were then subjected to fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions.Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and early crack growth due to FOD and subsequent fatigue loading were examined in detail. An analysis with a backscatter electron (BSE) detector was also carried out to investigate the microstructual deformation due to FOD, LSP, as well as the early fatigue crack growth mechanism in a complex residual stress field.

Computational simulation of the relaxation of local stresses due to foreign object damage under cyclic loading

In this study, the phenomenon of residual stress relaxation from foreign object damage (FOD) is numerically simulated using a hybrid explicit—implicit finite-element method. The effects of cycle fatigue loadings on stress relaxation were studied. FOD is first simulated by firing a 3mm cube impacting onto a plate made of titanium alloy Ti-6Al-4V at 200m/s. The FOD impact produces two distinct stress concentrations: one is compressive directly beneath the impact site; the other is tensile around the outer edge of the impact. The plate was then assumed to be subjected to a cyclic fatigue loading. The stress relaxation was investigated under a range of stress ratios and maximum applied stresses. Two different material models were considered for the simulations, namely an elastic—perfectly plastic model and a non-linear kinematic hardening model.

Index of Foreign Object Damage in Airfield Pavement Management

Control of foreign object damage (FOD) on airfield pavements is critical to the safety of aircraft operations. An index was developed to identify the FOD potential caused by deterioration of airfield pavements and was incorporated in airport pavement management systems. However, current pavement maintenance policies are determined mainly by the pavement condition index (PCI). This study investigates if the current practice of PCI-based pavement maintenance plans is able to address the maintenance required to reduce and contain FOD. This study includes 27.1 million square feet of airfield pavement at a commercial and a general aviation airport. It was observed that, in general, PCI-based pavement maintenance plans can accommodate the maintenance requirements triggered by FOD-related distresses. An innovative normalized PCI–FOD system was developed to identify efficiently sections that may be overlooked. It was determined that some pavement sections may require maintenance on the basis of FOD potential only although they have acceptable PCI values.

Full-Scale Field Testing for Injected Foam Stabilization of Portland Cement Concrete Repairs

A series of foam-injected repairs was performed on a portland cement concrete (PCC) test section at the U.S. Army Engineer Research and Development Center. Repairs consisted of uncompacted backfill overlaid by a 9-in. rapid-setting cementitious cap. A series of injection tubes was inserted through the cap into the uncompacted debris backfill, and a two-component rigid polyurethane foam was injected into this backfill. The test matrix compared the performance of three different repairs using various volumes of injected foam. A fourth repair was constructed without injected foam as a control item. Three hours after cap construction, the repairs underwent simulated aircraft traffic with an F-15E load cart. The performance of the four repairs was measured by passes to failure. The results of traffic testing were used to evaluate foam-injection technology for rapid repair of PCC pavements. The performances of foam-injected repairs were also compared with poured foam and traditional full-depth backfill repairs, each capped with rapid-setting materials. Comparisons were made about pavement performance, costs, and total duration required for installing the repair. Results showed that injection of excessive foam was detrimental to the repair surface, because it induced cracking before traffic application, and could lead to premature development of foreign object damage. However, repairs using moderate amounts of foam and pure backfill sustained the required traffic levels, defined by the research sponsor, of 200 passes within 4 h of initiating the pavement repair. For cost and repair duration, those repairs that did not include foam were more effective.

Comparison of Several Optimization Strategies for Robust Turbine Blade Design

This paper addresses the problem of turbine blade shape optimization in the presence of geometric uncertainties. Several strategies are tested and compared on a two-dimensional compressor blade optimization process for which performance is assessed using a commercial Reynolds-averaged Navier―Stokes computational fluid dynamics code. In each case, a range of shape errors are considered that attempt to simulate foreign object damage, erosion damage, and manufacturing errors. These lead to stochastic performance measures that, in turn, are considered in a multi-objective optimization framework. Because of the long run times associated with Reynolds-averaged Navier―Stokes codes, use is also made of surrogate or response-surface-based optimization methods to speed up the search processes. The paper shows that a range of techniques can be used to tackle this problem, but that no one method is clearly best overall. The practitioner is therefore cautioned against favoring a single approach for such design problems. Further research may help clarify these issues.