The development of fatigue testing technology has been a critical aspect of ensuring the safety and reliability of aircraft structures. This report provides a detailed overview of fatigue testing technology, including the different types of testing techniques and recent advancements in the field. The report also discusses the advantages and limitations of fatigue testing and highlights the importance of continuous research and development in this field. By identifying potential fatigue issues early and improving design and manufacturing processes, fatigue testing plays a crucial role in reducing maintenance costs and preventing catastrophic failures in aircraft structures.

1. DEVELOPMENT OF FATIGUE TESTING
TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China
Airlines Flight 611 (Case Study)
Submitted By: Abdul Majid
Student ID: S32002006W
Submitted To: Prof. Xueyi Zhang
Modern Mechanical Experimental Technology
School of Civil and Aerospace Engineering

2. Contents
Abstract.....................................................................................................................................................3
Introduction...............................................................................................................................................3
Overview of Fatigue Testing ....................................................................................................................3
Early Development of Fatigue Testing.....................................................................................................3
Advancements in Fatigue Testing Technology.........................................................................................3
Types of Fatigue Testing ..........................................................................................................................4
1. Constant Amplitude Fatigue Testing ............................................................................................4
2. Variable Amplitude Fatigue Testing.............................................................................................4
3. Spectrum Loading Fatigue Testing...............................................................................................4
Advantages and Limitations of Fatigue Testing .......................................................................................4
The advantages of fatigue testing include.............................................................................................4
Recent Advancements in Fatigue Testing Technology.............................................................................5
Conclusion ................................................................................................................................................5
Deadly Metal Fatigue: The Story of China Airlines Flight 611................................................................6
The Aircraft (B-18255).............................................................................................................................6
The Flight (CI 611)...................................................................................................................................6
Search and Recovery.................................................................................................................................7
Cause.........................................................................................................................................................7
Conclusion ................................................................................................................................................8
References...............................................................................................................................................14

3. DEVELOPMENT OF FATIGUE TESTING TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China Airlines Flight 611
3
Abstract
The development of fatigue testing technology has been a critical aspect of ensuring the
safety and reliability of aircraft structures. This report provides a detailed overview of fatigue
testing technology, including the different types of testing techniques and recent advancements in
the field. The report also discusses the advantages and limitations of fatigue testing and highlights
the importance of continuous research and development in this field. By identifying potential
fatigue issues early and improving design and manufacturing processes, fatigue testing plays a
crucial role in reducing maintenance costs and preventing catastrophic failures in aircraft
structures.
Introduction
Fatigue testing technology is an essential aspect of aircraft design and development. Fatigue
failures in aircraft structures can lead to catastrophic accidents, and therefore it is imperative to
identify and mitigate potential fatigue issues in aircraft. The development of fatigue testing
technology for aircraft has been a continuous process, with advancements in materials science and
technology driving the evolution of testing techniques. This report will provide an overview of the
development of fatigue testing technology for aircraft, including the various testing techniques,
their advantages and limitations, and recent advancements in the field.
Overview of Fatigue Testing
Fatigue testing is a method used to evaluate the structural integrity of materials and
components under cyclic loading. In the context of aircraft, fatigue testing is used to simulate the
stresses and strains that aircraft structures undergo during their lifespan, with the aim of identifying
potential fatigue issues. The testing process involves subjecting the material or component to
cyclic loading, with the load typically applied using a hydraulic or servo-hydraulic testing
machine. The testing can be performed in different ways, including axial loading, bending, torsion,
and combined loading. The test specimens are usually made from representative materials or
components, and their performance is monitored using strain gauges, accelerometers, or other
sensors.
Early Development of Fatigue Testing
The earliest fatigue testing techniques for aircraft were developed in the 1940s and 1950s.
At this time, fatigue testing was performed using simple machines that applied static loads to the
test specimens. These machines were not capable of simulating the dynamic loading conditions
experienced by aircraft structures, and therefore their use was limited. In the 1960s, servo-
hydraulic testing machines were developed, which allowed for more realistic testing of aircraft
structures. These machines were capable of applying cyclic loads to the test specimens, and their
use revolutionized the field of fatigue testing.
Advancements in Fatigue Testing Technology

4. Over the years, there have been several advancements in fatigue testing technology for
aircraft. One of the most significant advancements has been the development of digital control
systems for testing machines. These systems allow for precise control of loading and monitoring
of test specimens, and they have improved the accuracy and repeatability of fatigue testing.
Another significant advancement has been the development of computer-aided testing
(CAT) systems. These systems use computer simulations to predict the performance of materials
and components under different loading conditions. CAT systems have reduced the need for
physical testing and have allowed for faster and more efficient evaluation of materials and
components.
In recent years, there has been a growing interest in the use of non-destructive testing
(NDT) techniques for fatigue testing. NDT techniques, such as ultrasonic testing and X-ray
radiography, can detect potential fatigue issues in materials and components without causing
damage to them. These techniques have the potential to reduce the cost and time required for
fatigue testing, and they are being increasingly used in the aerospace industry.
Types of Fatigue Testing
There are several types of fatigue testing techniques used in the aerospace industry, including:
1. Constant Amplitude Fatigue Testing
Constant amplitude fatigue testing involves subjecting the test specimen to a constant cyclic
load amplitude. This type of testing is typically used to evaluate the endurance limit of materials
and components.
2. Variable Amplitude Fatigue Testing
Variable amplitude fatigue testing involves subjecting the test specimen to cyclic loading with
varying amplitudes. This type of testing is used to evaluate the fatigue life of materials and
components under realistic loading conditions.
3. Spectrum Loading Fatigue Testing
Spectrum loading fatigue testing involves subjecting the test specimen to cyclic loading that
simulates the loading conditions experienced by the aircraft structure during its lifespan. This type
of testing is the most realistic and is used to evaluate the performance of materials and components
under actual loading conditions.
Advantages and Limitations of Fatigue Testing
The advantages of fatigue testing include
1. Identification of potential fatigue issues before they become critical: Fatigue testing can
help identify potential fatigue issues in materials and components before they cause
catastrophic failures, allowing for preventive maintenance and repairs.

5. DEVELOPMENT OF FATIGUE TESTING TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China Airlines Flight 611
5
2. Improvement of design and manufacturing processes: Fatigue testing can provide valuable
data that can be used to improve the design and manufacturing processes of aircraft
structures, resulting in stronger and safer aircraft.
3. Reduction of maintenance costs: By identifying potential fatigue issues early, fatigue
testing can help reduce maintenance costs by allowing for targeted repairs and
replacements.
However, there are also limitations to fatigue testing:
1. Cost: Fatigue testing can be expensive, particularly when spectrum loading fatigue testing
is required.
2. Time-consuming: Fatigue testing can take a significant amount of time, particularly when
spectrum loading fatigue testing is required.
3. Limited to known loading conditions: Fatigue testing is limited to known loading
conditions, and it may not be able to accurately predict the performance of materials and
components under unknown or unforeseen loading conditions.
Recent Advancements in Fatigue Testing Technology
Recent advancements in fatigue testing technology have focused on improving the
accuracy and efficiency of testing techniques. One such advancement is the use of high-frequency
fatigue testing, which involves subjecting the test specimen to cyclic loading at high frequencies
(typically above 20 kHz). High-frequency fatigue testing can simulate the high-frequency
vibrations that aircraft structures are exposed to during flight, and it can provide more accurate
data on the fatigue behavior of materials and components.
Another recent advancement is the use of multi-axial fatigue testing, which involves
subjecting the test specimen to cyclic loading in multiple directions simultaneously. Multi-axial
fatigue testing can provide more realistic data on the fatigue behavior of materials and components,
particularly those that are subjected to complex loading conditions.
Conclusion
Fatigue testing technology is an essential aspect of aircraft design and development. It
allows for the identification and mitigation of potential fatigue issues in aircraft structures,
reducing the risk of catastrophic failures. The development of fatigue testing technology has been
a continuous process, with advancements in materials science and technology driving the evolution
of testing techniques. There are several types of fatigue testing techniques used in the aerospace
industry, including constant amplitude, variable amplitude, and spectrum loading fatigue testing.
Recent advancements in fatigue testing technology have focused on improving the accuracy and
efficiency of testing techniques, including the use of high-frequency fatigue testing and multi-axial
fatigue testing. While there are limitations to fatigue testing, its advantages in improving aircraft
safety and reducing maintenance costs make it an essential aspect of aircraft design and
development.

6. Deadly Metal Fatigue: The Story of China Airlines Flight 611
Flight 611 saw a Boeing 747-200 break up in midair, later found to be the result of a tail
strike 20 years before.
China Airlines 611 was a regular, scheduled flight between Taipei - Chiang Kai-shek
International Airport (TPE) and Hong Kong - Chep Lap Kok International Airport (HKG).
Operated by a Boeing 747-209B, the aircraft crashed into the Taiwan Strait, which separates the
island of Taiwan from mainland China, due to metal fatigue in the fuselage. This accident killed
all 225 people onboard the aircraft, including 206 passengers and 19 crew members.
The Aircraft (B-18255)
The Boeing 747-200 that was operating on the route (registration: B-18255, originally
registered as B-1866) was the only remaining aircraft of this type in the fleet, as the others had
been converted to freighters operating for the cargo division of China Airlines. B-18255 was
actually operating its last commercial flight for China Airlines, and had been sold to Orient Thai
Airlines, a charter airline based in Bangkok, Thailand. The aircraft was to return to Taipei after the
flight to Hong Kong, and would then be under the control of Orient Thai Airlines. This,
unfortunately did not happen.
This aircraft had been delivered to China Airlines in 1979, and had logged 64,394 airframe
hours, according to aviation-safety.net. It had operated 21,180 flight cycles prior to this flight.
The Flight (CI 611)

7. DEVELOPMENT OF FATIGUE TESTING TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China Airlines Flight 611
7
This flight was relatively routine for China Airlines, as this route was operated multiple
times daily. In addition, the weather conditions were reported as fine and relatively warm, and
therefore weather wasn't a safety concern.
The majority of passengers and all crew members (209 of 225) were Taiwanese. Some
passengers were Chinese and some were residents of Hong Kong. 114 passengers were tourists
traveling to China on scheduled tours, and other prominent passengers on this service included a
Taiwanese legislator and a politician.
At 15:16, the flight was cleared to climb to about 35,000 feet (11,000 m). Three minutes
later, the aircraft broke up in midair and contact was lost. Almost all remains were recovered, and
flight recovery teams reported that most victims had extensive head wounds and injuries, but there
had been no reports of foul play or fire.
Search and Recovery
Since this accident happened in busy airspace, other nearby aircraft could see the crash site,
and reported it to authorities. At 18:10, first responders were on scene and had found the remains
of some victims. The governments of the People's Republic of China (mainland China) and the
Republic of China (Taiwan) cooperated on this search, and this certainly did expedite the process
of identifying the victims. China Airlines also requested that relatives of victims send blood
samples to laboratories to help with victim identification. To date, 175 of the 225 victims' remains
have been identified.
Figure 1 Safety authorities reconstructed as much of the fuselage as possible to figure out what went wrong.
Cause
Following the crash, an extensive investigation was launched. The final report cited
inadequate maintenance as the main cause.

8. In February 1980, 20 years previous, the aircraft had operating flight CI 009 from
Stockholm Arlanda Airport (ARN) to Taoyuan International Airport (TPE) via Jeddah and Hong
Kong when it suffered a tail strike. On landing at Kai Tak Airport (demolished, formerly HKG),
one of its two stops on this route, the plane's tail had scraped along the runway.
Instead of carrying out proper maintenance on the aircraft, the China Airlines engineering
team simply installed a doubler over the damaged part of the aircraft. This was not sufficient
according to Boeing's Structural Repair Manual (SRM). The constant use of the aircraft had
enlarged the crack within the aircraft, which eventually led to the aircraft breaking up midair two
whole decades later.
Conclusion
This accident sent shock waves through the aviation community, as it emphasized the
importance of proper maintenance on aircraft, particularly aircraft that are involved in accidents.
The Republic of China's Civil Aviation Administration (CAA) grounded all the Boeing 747-200
within China Airlines' fleet to ensure that they didn't have any cracks.
The crash of China Airlines flight 611
Figure 2 The cockpit of China Airlines flight 611 is recovered from the Taiwan Strait in 2002. (Aviation Safety Council)
On the 25th of May 2002, a China Airlines Boeing 747 abruptly disintegrated at 35,000
feet over the Taiwan Strait, killing all 225 people on board in the latest blow to the airline’s already
troubled safety record. But while China Airlines was infamous for accidents due to poor
airmanship, this one immediately struck experts as different. Indeed, everything was normal
aboard flight 611 up until the moment it abruptly split in two, spewing debris across hundreds of
square kilometers as the crippled remains of the plane plummeted toward the sea. And yet there
was no explosion, no collision, nothing that would cause a 747 to simply fall apart. Unlocking the

9. DEVELOPMENT OF FATIGUE TESTING TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China Airlines Flight 611
9
secret of its demise would require painstaking forensic analysis of the debris, piecing together
when and how each ravaged strip of metal broke away from the plane, until finally investigators
zeroed in on the source of the rot which had been eating through the aircraft’s structure until it
could no longer hold itself together. There they would learn that China Airlines flight 611 was a
slow-moving catastrophe, building incrementally for 22 years, out of sight and out of mind, until
it reached an invisible tipping point, and at last with a great burst of violence the Boeing 747 was
shattered in seconds.
Figure 3 A CGI image of B-1866 striking its tail on the runway in 1980. (Mayday)
Figure 4 The location of the doubler placed over the tail strike damage. (Aviation Safety Council)

10. The only place where China Airlines could carry out such a repair was at its base of
operations at Chiang Kai-shek International Airport in Taipei. Airline management quickly
resolved to bring it there, and on the same day as the incident the plane was ferried, unpressurized
and without passengers, from Hong Kong back to Taipei, flying at low altitude the whole way
across the Taiwan Strait.
After arriving in Taipei, engineers assessed the damage, and the following day a temporary
repair was carried out. Intended to render the plane airworthy only until downtime could be found
to implement a more permanent solution, the temporary repair consisted of a series of aluminum
doubler plates riveted over the scratched fuselage skin.
The skin of an airplane is a key structural element and the primary absorber of the stresses
associated with pressurization. The stress placed on the skin when the cabin is pressurized is
considerable, on the order of 9 pounds per square inch, and any section unable to withstand the
repeated application of this force will quickly fail. If an area of fuselage skin is damaged, the most
reliable way to prevent it from failing under pressurization loads is to cover it with a doubler plate
— an extra layer of skin which redirects these stresses around the damaged area. Doubler plates
are ubiquitous in aviation maintenance, and if you look closely at any plane with an extensive
service history you will find at least a few, and sometimes dozens.
The temporary repair to B-1866 remained in place for about three and a half months, before
the plane was taken in for more extensive servicing in May 1980. The damaged area was sanded
down to remove any sharp edges, and the aluminum plates installed in February were swapped for
a new, larger doubler. An inspector signed off on the work, and B-1866 was cleared to fly. No one
at the workshop that day could have realized that they had just set in motion a chain of events that
would not bear its bitter fruit until long after every one of them had retired.

11. DEVELOPMENT OF FATIGUE TESTING TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China Airlines Flight 611
11
Figure 5 The route and crash site of flight 611.
With a thunderous boom, a hole opened up in the tail of the aircraft, circling all the way
around the fuselage until the entire tail section, including all the flight controls and a sizeable
chunk of the economy class cabin, simply fell off. A tremendous burst of wind swept through the
plane, tearing away anything and anyone that was not strapped down. Debris spewed rearward into
the wide open sky as the crippled plane abruptly pitched down into an irrecoverable dive. For
fifteen more seconds, a radar station in Xiamen, China continued to receive transponder returns
from the plane, indicating a rapid descent, before powerful G-forces ripped off all four engines at
a height of 29,000 feet, cutting power to the avionics. The pilots probably kept trying to fly, but
we will never know for sure. Their efforts would have been futile, as the shuddering hulk of what
had once been their plane spiraled down toward the sea, missing its engines, missing its flight
controls, a gaping hole staring out into the infinite blue where the tail section used to be. The pilots
probably never knew that everything aft of the wings was gone, and even if they had, it would
have made no difference, for two and a half minutes later, what was left of flight 611 slammed
into the Taiwan Strait and disappeared beneath the waves.

12. Figure 6 Officials carry a piece of flight 611 on shore in Magong. (CBS News)
Figure 7 Color-coded diagram of the three main wreckage zones, and which parts of the plane were found within them.
(Aviation Safety Council)

13. DEVELOPMENT OF FATIGUE TESTING TECHNOLOGY FOR A FATIGUE ISSUE
Shattered in Seconds: The Crash of China Airlines Flight 611
13
Figure 8 the fatigue cracking on item 640 vs. normal fatigue cracking. (Aviation Safety Council)
But here investigators noticed something highly unusual about the way the fatigue cracks
grew. Most fatigue cracks, having initiated at the surface of the skin, quickly penetrate the skin’s
entire thickness and then spread laterally through the material. In contrast, the multiple-site damage
under the doubler on B-18255 grew in a totally different fashion: the cracks started out very long
but also very shallow, and then slowly increased in depth with every cycle, rather than increasing
in length. Although the cracks did get longer over time, this was not their primary direction of
growth.

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