Published on March 13, 2014
STRUCTUTAL HEALTH MONITORING FOR AEROSPACE VEHICLES
What is structural health monitoring? • The ability to monitor damage, assess structural health and diagnose damage conditions What is structural health management? • Taking action in response to damage, form a prognosis, make a decision and take remedial action How do they differ from current practice? • Currently based on periodic inspection • First Step - Conditioned Based Maintenance
Sensor Net-work SHM is the imitation of the human nervous system
The Three key subsystems of SHM
Diagnosis: subsystem deals with monitoring of the entire structure under inspection. It has an underlying wired/ wireless network of sensors and a variety of sensing mechanisms need to be adopted for different sections of aircraft. Periodic measurements are tapped from these in-situ sensors either through wired or wireless media into a centralized analysis station in the SHM system. Prognosis: subsystem takes the periodic inspection data from diagnosis subsystem to analyze and estimate various possible internal and external damages that might have occurred in the structure. The estimated damage characteristics are used in the damage evolution models to estimate the remaining life of the structure as well as to find a necessity to trigger maintenance. Life Extension & Predictive Maintenance: The damage evolution models are effectively combined with probability of detection (POD) models for structural integrity assessment and remaining life assessment. Cost-benefit analysis is performed to arrive at a tradeoff between the safety allowance and maintenance costs to be incurred while triggering maintenance in the given conditions
SHM IN AIRCRAFT MAINTENANCE • Due to various stress conditions during the flight, aircraft structures develop various kinds of defects which include stress corrosion, cracks, accidental damage, impact damage, delamination’s, deboning’s, water ingress, damage due to loads/strain. • A thorough inspection schedule is instructed by the aircraft manufacturer, which include various types of checks as shown in Figure below. • The current state of the art in the schedule-based inspection and maintenance is to conduct time-based localized inspection of few selected parts of the structure. Hence, at any given point of time, it is difficult to comprehensively understand the structure’s health in totality.
Aircraft Maintenance checks (Periodic Inspection)
• Schedule based maintenance works well during designed service life. However, over time, the focus shifts towards life extension i.e. need to use aircraft longer than planned or to use it for different missions than designed. • As Aging aircrafts continue in service, they result in increased inspection time, increased operations and maintenance costs and decreased availability, due to higher risk of hazard. • Such high risk of hazard and maintenance costs can be minimized by employing a continuous online monitoring technique which triggers the maintenance schedule as and when required. • SHM enables condition based maintenance with a capability to initiate inspection requirements not only based on the scheduled intervals, but also on actual wear indicators exhibited by the equipment at that given point of time.
Issues Related to the Aging Infrastructure
SHM technology helps in • Increased availability of the aircraft • Effective assessment of actual damage events • Reduced costs of life-cycle and total ownership • Reduced logistics • Increased safety and reliability Moving beyond preventive maintenance into predictive maintenance, in-situ Structural Health Monitoring (SHM) can provide • Long-term cost savings and • Extended fleet life. Thus, SHM will enable new maintenance concepts.
Benefits of SHM (Structural health monitoring) over NDT (Non-destructive Testing)
Importance of SHM SHM improves - safety & functionality of structures. Monitoring - develop innovative design methodologies - timely warning of impending failures. Structural condition monitoring and assessment are required for timely and cost-effective maintenance.
Embedment of sensors during construction and measurement of structural responses during service will enable condition assessment and remaining life estimation easy and convenient Monitoring scheme helps to gather data on the realistic performance of the structures, which in turn will help to design better structures for the future.
29 October 2004 Where have we come from in the last 100 years? Wright Bros., Kitty Hawk, 17 December 1903 Boeing 7E7 2008 Where will we be in 50-100 years? Boeing 747 1970s Where are we now?
• Future aerospace vehicles will Re-configurable (morphing) Structural Self Assessment Self Repair Intelligent adaptive response • This requires multi-functional material and structures Active/sensory/structural Embedded intelligence • Biomimetic functionality is being explored for ways to achieve this.
29 October 2004 Bio/Nano/Thinking/Sensing Vehicle
CONCLUSION • SHM as a concept is matured and now identified as one of the key enabling technologies to ensure the integrity of future aircraft structures. • SHM along with advanced alloys, composites and hybrid materials will revolutionize both airframe and engine structures of future aircrafts. • SHM can help in increasing the structural allowable with higher confidence removing the conservatism in the current designs. This will reduce structural weight leading to reduced acquisition and maintenance costs. • SHM enabled structures need to be designed differently using integrated systems approach considering both mechanical aspects of structure and sensor technologies. • The sensor integration with structure is very critical and sensor locations should not become damage initiation locations. • Use of SHM can translate to over 40% of reduction in the maintenance cost through inspection time and cost savings. • Thus SHM is one of the enabling technologies to revolutionize the future aircraft design, development and maintenance.
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