Forensic engineering
Encyclopedia
Forensic engineering is the investigation of materials, products
, structure
s or components that fail or do not operate or function as intended, causing personal injury
or damage to property. The consequences of failure are dealt with by the law of product liability
. The field also deals with retracing processes and procedures leading to accidents in operation of vehicles or machinery. The subject is applied most commonly in civil law
cases, although may be of use in criminal law
cases. Generally the purpose of a Forensic
engineering
investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident
. It can also involve investigation of intellectual property
claims, especially patent
s.
(1877–1966) was a pioneer in forensic science who formulated the basic principle of forensic science: "Every contact leaves a trace". This became known as Locard's exchange principle.
and fault tree analysis
methods also examine product or process failure in a structured and systematic way, in the general context of safety engineering
. However, all such techniques rely on accurate reporting of failure rate
s, and precise identification, of the failure modes involved.
There is some common ground between forensic science and forensic engineering, such as scene of crime and scene of accident analysis, integrity of the evidence and court appearances. Both disciplines make extensive use of optical and scanning electron microscope
s, for example. They also share common use of spectroscopy
(infra-red, ultra-violet and nuclear magnetic resonance) to examine critical evidence. Radiography
using X-ray
s or neutron
s is also very useful in examining thick products for their internal defects before destructive examination is attempted. Often, however, a simple hand lens
to reveal the cause of a particular problem.
Trace evidence
is sometimes an important factor in reconstructing the sequence of events in an accident. For example, tire burn marks on a road surface can enable vehicle speeds to be estimated, when the brakes were applied and so on. Ladder feet often leave a trace of movement of the ladder during a slipaway, and may show how the accident occurred. When a product fails for no obvious reason, SEM
and Energy-dispersive X-ray spectroscopy
(EDX) performed in the microscope can reveal the presence of aggressive chemicals that have left traces on the fracture or adjacent surfaces. Thus an acetal resin water pipe joint suddenly failed and caused substantial damages to a building in which it was situated. Analysis of the joint showed traces of chlorine, indicating a stress corrosion cracking
failure mode. The failed fuel pipe junction mentioned above showed traces of sulfur
on the fracture surface from the sulfuric acid
, which had initiated the crack.
Forensic materials engineering
involves methods applied to specific materials, such as metal
s, glass
es, ceramic
s, composites
and polymer
s.
The broken fuel pipe shown at left caused a serious accident when diesel fuel poured out from a van onto the road. A following car skidded and the driver was seriously injured when she collided with an oncoming lorry. Scanning electron microscopy or SEM showed that the nylon
connector had fractured by stress corrosion cracking
(SCC) due to a small leak of battery acid. Nylon is susceptible to hydrolysis
when in contact with sulfuric acid
, and only a small leak of acid would have sufficed to start a brittle crack in the injection moulded nylon 6,6 connector by SCC. The crack took about 7 days to grow across the diameter of the tube, hence the van driver should have seen the leak well before the crack grew to a critical size. He did not, thereby resulting in the accident. The fracture surface showed a mainly brittle surface with striations indicating progressive growth of the crack across the diameter of the pipe. Once the crack had penetrated the inner bore, fuel started leaking onto the road.
The nylon 6,6 had been attacked by the following reaction, which was catalysed by the acid:
Diesel fuel is especially hazardous on road surfaces because it forms a thin oily film that cannot be easily seen by drivers. It is akin to black ice
in lubricity, so skids are common when diesel leaks occur. The insurers of the van driver admitted liability and the injured driver was compensated.
s such as bridge and building collapses) are subject to forensic investigation by engineers experienced in forensic methods of investigation. Rail crashes, aviation accidents
, and some automobile accidents
are investigated by forensic engineers in particular where component failure is suspected. Furthermore, appliances, consumer products, medical devices, structures, industrial machinery, and even simple hand tools such as hammers or chisels can warrant investigations upon incidents causing injury or property damages. The failure of medical device
s is often safety-critical
to the user, so reporting failures and analysing them is particularly important. The environment of the body is complex, and implants
must both survive this environment, and not leach potentially toxic impurities. Problems have been reported with breast implants, heart valve
s, and catheter
s, for example.
Failures that occur early in the life of a new product are vital information for the manufacturer to improve the product. New product development
aims to eliminate defects by testing in the factory before launch, but some may occur during its early life. Testing products to simulate their behavior in the external environment is a difficult skill, and may involve accelerated life testing
for example. The worst kind of defect to occur after launch is a safety-critical
defect, a defect that can endanger life or limb. Their discovery usually leads to a product recall
or even complete withdrawal of the product from the market. Product defects often follow the bathtub curve
, with high initial failures, a lower rate during regular life, followed by another rise due to wear-out. National standards, such as those of ASTM
and the British Standards Institute
, and International Standard
s can help the designer in increasing product integrity.
There are many examples of forensic methods used to investigate accidents and disasters, one of the earliest in the modern period being the fall of the Dee bridge at Chester
, England
. It was built using cast iron
girder
s, each of which was made of three very large castings dovetailed together. Each girder was strengthened by wrought iron
bars along the length. It was finished in September 1846, and opened for local traffic after approval by the first Railway Inspector, General Charles Pasley. However, on 24 May 1847, a local train to Ruabon
fell through the bridge. The accident resulted in five deaths (three passengers, the train guard, and the locomotive fireman) and nine serious injuries. The bridge had been designed by Robert Stephenson
, and he was accused of negligence by a local inquest
.
Although strong in compression, cast iron was known to be brittle in tension or bending, yet, on the day of the accident, the bridge deck was covered with track ballast to prevent the oak beams supporting the track from catching fire. Stephenson took this precaution because of a recent fire on the Great Western Railway at Uxbridge, London, where Isambard Kingdom Brunel's bridge caught fire and collapsed. This act imposed a heavy extra load on the girders supporting the bridge, and probably exacerbated the accident.
One of the first major inquiries conducted by the newly formed Railway Inspectorate was conducted by Captain Simmons of the Royal Engineers
, and his report suggested that repeated flexing of the girder weakened it substantially. He examined the broken parts of the main girder, and confirmed that the girder had broken in two places, the first break occurring at the center. He tested the remaining girders by driving a locomotive across them, and found that they deflected by several inches under the moving load. He concluded that the design was flawed, and that the wrought iron trusses fixed to the girders did not reinforce the girders at all, which was a conclusion also reached by the jury at the inquest. Stephenson's design had depended on the wrought iron trusses to strengthen the final structures, but they were anchored on the cast iron girders themselves, and so deformed with any load on the bridge. Others (especially Stephenson) argued that the train had derailed and hit the girder, the impact force
causing it to fracture
. However, eye witnesses maintained that the girder broke first and the fact that the locomotive
remained on the track showed otherwise.
Another notable publication, dealing with failures of buildings, bridges, and other structures, is the Journal of Performance of Constructed Facilities,
which is published by the American Society of Civil Engineers, under the umbrella of its Technical Council on Forensic Engineering.
Product (business)
In general, the product is defined as a "thing produced by labor or effort" or the "result of an act or a process", and stems from the verb produce, from the Latin prōdūce ' lead or bring forth'. Since 1575, the word "product" has referred to anything produced...
, structure
Structure
Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...
s or components that fail or do not operate or function as intended, causing personal injury
Personal injury
Personal injury is a legal term for an injury to the body, mind or emotions, as opposed to an injury to property. The term is most commonly used to refer to a type of tort lawsuit alleging that the plaintiff's injury has been caused by the negligence of another, but also arises in defamation...
or damage to property. The consequences of failure are dealt with by the law of product liability
Product liability
Product liability is the area of law in which manufacturers, distributors, suppliers, retailers, and others who make products available to the public are held responsible for the injuries those products cause...
. The field also deals with retracing processes and procedures leading to accidents in operation of vehicles or machinery. The subject is applied most commonly in civil law
Civil law (common law)
Civil law, as opposed to criminal law, is the branch of law dealing with disputes between individuals or organizations, in which compensation may be awarded to the victim...
cases, although may be of use in criminal law
Criminal law
Criminal law, is the body of law that relates to crime. It might be defined as the body of rules that defines conduct that is not allowed because it is held to threaten, harm or endanger the safety and welfare of people, and that sets out the punishment to be imposed on people who do not obey...
cases. Generally the purpose of a Forensic
Forensics
Forensic science is the application of a broad spectrum of sciences to answer questions of interest to a legal system. This may be in relation to a crime or a civil action...
engineering
Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident
Accident
An accident or mishap is an unforeseen and unplanned event or circumstance, often with lack of intention or necessity. It implies a generally negative outcome which may have been avoided or prevented had circumstances leading up to the accident been recognized, and acted upon, prior to its...
. It can also involve investigation of intellectual property
Intellectual property
Intellectual property is a term referring to a number of distinct types of creations of the mind for which a set of exclusive rights are recognized—and the corresponding fields of law...
claims, especially patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
s.
History
As the field of engineering has evolved over time so has the field of forensic engineering. With the prevalence of liability lawsuits in the late 1900's the use of forensic engineering as a means to determine culpability spread in the courts. Dr. Edmond LocardEdmond Locard
Dr. Edmond Locard was a pioneer in forensic science who became known as the Sherlock Holmes of France. He formulated the basic principle of forensic science: "Every contact leaves a trace"...
(1877–1966) was a pioneer in forensic science who formulated the basic principle of forensic science: "Every contact leaves a trace". This became known as Locard's exchange principle.
Investigation
Vital to the field of forensic engineering is the process of investigating and collecting data related to the materials, products, structures or components that failed. This involves inspections, collecting evidence, measurements, developing models, obtaining exemplar products, and performing experiments. Often testing and measurements are conducted in an Independent testing laboratory or other reputable unbiased laboratory.Analysis
FMEAFailure mode and effects analysis
A failure modes and effects analysis is a procedure in product development and operations management for analysis of potential failure modes within a system for classification by the severity and likelihood of the failures...
and fault tree analysis
Fault tree analysis
Fault tree analysis is a top down, deductive failure analysis in which an undesired state of a system is analyzed using boolean logic to combine a series of lower-level events...
methods also examine product or process failure in a structured and systematic way, in the general context of safety engineering
Safety engineering
Safety engineering is an applied science strongly related to systems engineering / industrial engineering and the subset System Safety Engineering...
. However, all such techniques rely on accurate reporting of failure rate
Failure rate
Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. It is often denoted by the Greek letter λ and is important in reliability engineering....
s, and precise identification, of the failure modes involved.
There is some common ground between forensic science and forensic engineering, such as scene of crime and scene of accident analysis, integrity of the evidence and court appearances. Both disciplines make extensive use of optical and scanning electron microscope
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
s, for example. They also share common use of spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
(infra-red, ultra-violet and nuclear magnetic resonance) to examine critical evidence. Radiography
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
using X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s or neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s is also very useful in examining thick products for their internal defects before destructive examination is attempted. Often, however, a simple hand lens
Magnifying glass
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle ....
to reveal the cause of a particular problem.
Trace evidence
Trace evidence
Trace evidence is evidence that occurs when different objects contact one another. Such materials are often transferred by heat induced by contact friction....
is sometimes an important factor in reconstructing the sequence of events in an accident. For example, tire burn marks on a road surface can enable vehicle speeds to be estimated, when the brakes were applied and so on. Ladder feet often leave a trace of movement of the ladder during a slipaway, and may show how the accident occurred. When a product fails for no obvious reason, SEM
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
and Energy-dispersive X-ray spectroscopy
Energy-dispersive X-ray spectroscopy
Energy-dispersive X-ray spectroscopy is an analytical technique used for the elemental analysis or chemical characterization of a sample. It relies on the investigation of an interaction of a some source of X-ray excitation and a sample...
(EDX) performed in the microscope can reveal the presence of aggressive chemicals that have left traces on the fracture or adjacent surfaces. Thus an acetal resin water pipe joint suddenly failed and caused substantial damages to a building in which it was situated. Analysis of the joint showed traces of chlorine, indicating a stress corrosion cracking
Stress corrosion cracking
Stress corrosion cracking is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when...
failure mode. The failed fuel pipe junction mentioned above showed traces of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
on the fracture surface from the sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
, which had initiated the crack.
Forensic materials engineering
Forensic materials engineering
A branch of Forensic engineering, the subject focuses on the material evidence from crime or accident scenes, seeking defects in those materials which might explain why an accident occurred, or the source of a specific material to identify a criminal...
involves methods applied to specific materials, such as metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s, glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
es, ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s, composites
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
and polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
s.
Examples
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
connector had fractured by stress corrosion cracking
Stress corrosion cracking
Stress corrosion cracking is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when...
(SCC) due to a small leak of battery acid. Nylon is susceptible to hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
when in contact with sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
, and only a small leak of acid would have sufficed to start a brittle crack in the injection moulded nylon 6,6 connector by SCC. The crack took about 7 days to grow across the diameter of the tube, hence the van driver should have seen the leak well before the crack grew to a critical size. He did not, thereby resulting in the accident. The fracture surface showed a mainly brittle surface with striations indicating progressive growth of the crack across the diameter of the pipe. Once the crack had penetrated the inner bore, fuel started leaking onto the road.
The nylon 6,6 had been attacked by the following reaction, which was catalysed by the acid:
Diesel fuel is especially hazardous on road surfaces because it forms a thin oily film that cannot be easily seen by drivers. It is akin to black ice
Black ice
Black ice, sometimes called glare ice or clear ice, refers to a thin coating of glazed ice on a surface.While not truly black, it is virtually transparent, allowing black asphalt/macadam roadways to be seen through it, hence the term "black ice"...
in lubricity, so skids are common when diesel leaks occur. The insurers of the van driver admitted liability and the injured driver was compensated.
Applications
Most manufacturing models will have a forensic component that monitors early failures to improve quality or efficiencies. Insurance companies use forensic engineers to prove liability or nonliability. Most engineering disasters (structural failureStructural failure
Structural failure refers to loss of the load-carrying capacity of a component or member within a structure or of the structure itself. Structural failure is initiated when the material is stressed to its strength limit, thus causing fracture or excessive deformations...
s such as bridge and building collapses) are subject to forensic investigation by engineers experienced in forensic methods of investigation. Rail crashes, aviation accidents
Aviation accidents and incidents
An aviation accident is defined in the Convention on International Civil Aviation Annex 13 as an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, in which a...
, and some automobile accidents
Car accident
A traffic collision, also known as a traffic accident, motor vehicle collision, motor vehicle accident, car accident, automobile accident, Road Traffic Collision or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other stationary obstruction,...
are investigated by forensic engineers in particular where component failure is suspected. Furthermore, appliances, consumer products, medical devices, structures, industrial machinery, and even simple hand tools such as hammers or chisels can warrant investigations upon incidents causing injury or property damages. The failure of medical device
Medical device
A medical device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery . Whereas medicinal products achieve their principal action by pharmacological, metabolic or immunological means. Medical devices act by other means like physical, mechanical, thermal,...
s is often safety-critical
Life-critical system
A life-critical system or safety-critical system is a system whose failure ormalfunction may result in:* death or serious injury to people, or* loss or severe damage to equipment or* environmental harm....
to the user, so reporting failures and analysing them is particularly important. The environment of the body is complex, and implants
Implant (medicine)
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue...
must both survive this environment, and not leach potentially toxic impurities. Problems have been reported with breast implants, heart valve
Heart valve
A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...
s, and catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
s, for example.
Failures that occur early in the life of a new product are vital information for the manufacturer to improve the product. New product development
New product development
In business and engineering, new product development is the term used to describe the complete process of bringing a new product to market. A product is a set of benefits offered for exchange and can be tangible or intangible...
aims to eliminate defects by testing in the factory before launch, but some may occur during its early life. Testing products to simulate their behavior in the external environment is a difficult skill, and may involve accelerated life testing
Accelerated life testing
Accelerated life testing is the process of testing a product by subjecting it to conditions in excess of its normal service parameters in an effort to uncover faults and potential modes of failure in a short amount of time...
for example. The worst kind of defect to occur after launch is a safety-critical
Life-critical system
A life-critical system or safety-critical system is a system whose failure ormalfunction may result in:* death or serious injury to people, or* loss or severe damage to equipment or* environmental harm....
defect, a defect that can endanger life or limb. Their discovery usually leads to a product recall
Product recall
A product recall is a request to return to the maker a batch or an entire production run of a product, usually due to the discovery of safety issues. The recall is an effort to limit liability for corporate negligence and to improve or avoid damage to publicity...
or even complete withdrawal of the product from the market. Product defects often follow the bathtub curve
Bathtub curve
The bathtub curve is widely used in reliability engineering. It describes a particular form of the hazard function which comprises three parts:*The first part is a decreasing failure rate, known as early failures....
, with high initial failures, a lower rate during regular life, followed by another rise due to wear-out. National standards, such as those of ASTM
ASTM International
ASTM International, known until 2001 as the American Society for Testing and Materials , is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services...
and the British Standards Institute
BSI Group
BSI Group, also known in its home market as the British Standards Institution , is a multinational business services provider whose principal activity is the production of standards and the supply of standards-related services.- History :...
, and International Standard
International standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
s can help the designer in increasing product integrity.
Historic examples
Chester
Chester is a city in Cheshire, England. Lying on the River Dee, close to the border with Wales, it is home to 77,040 inhabitants, and is the largest and most populous settlement of the wider unitary authority area of Cheshire West and Chester, which had a population of 328,100 according to the...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. It was built using cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
girder
Girder
A girder is a support beam used in construction. Girders often have an I-beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams...
s, each of which was made of three very large castings dovetailed together. Each girder was strengthened by wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...
bars along the length. It was finished in September 1846, and opened for local traffic after approval by the first Railway Inspector, General Charles Pasley. However, on 24 May 1847, a local train to Ruabon
Ruabon
Ruabon is a village and community in the county borough of Wrexham in Wales.More than 80% of the population of 2,400 were born in Wales with 13.6% speaking Welsh....
fell through the bridge. The accident resulted in five deaths (three passengers, the train guard, and the locomotive fireman) and nine serious injuries. The bridge had been designed by Robert Stephenson
Robert Stephenson
Robert Stephenson FRS was an English civil engineer. He was the only son of George Stephenson, the famed locomotive builder and railway engineer; many of the achievements popularly credited to his father were actually the joint efforts of father and son.-Early life :He was born on the 16th of...
, and he was accused of negligence by a local inquest
Inquest
Inquests in England and Wales are held into sudden and unexplained deaths and also into the circumstances of discovery of a certain class of valuable artefacts known as "treasure trove"...
.
Although strong in compression, cast iron was known to be brittle in tension or bending, yet, on the day of the accident, the bridge deck was covered with track ballast to prevent the oak beams supporting the track from catching fire. Stephenson took this precaution because of a recent fire on the Great Western Railway at Uxbridge, London, where Isambard Kingdom Brunel's bridge caught fire and collapsed. This act imposed a heavy extra load on the girders supporting the bridge, and probably exacerbated the accident.
One of the first major inquiries conducted by the newly formed Railway Inspectorate was conducted by Captain Simmons of the Royal Engineers
Royal Engineers
The Corps of Royal Engineers, usually just called the Royal Engineers , and commonly known as the Sappers, is one of the corps of the British Army....
, and his report suggested that repeated flexing of the girder weakened it substantially. He examined the broken parts of the main girder, and confirmed that the girder had broken in two places, the first break occurring at the center. He tested the remaining girders by driving a locomotive across them, and found that they deflected by several inches under the moving load. He concluded that the design was flawed, and that the wrought iron trusses fixed to the girders did not reinforce the girders at all, which was a conclusion also reached by the jury at the inquest. Stephenson's design had depended on the wrought iron trusses to strengthen the final structures, but they were anchored on the cast iron girders themselves, and so deformed with any load on the bridge. Others (especially Stephenson) argued that the train had derailed and hit the girder, the impact force
Impact force
In mechanics, an impact is a high force or shock applied over a short time period when two or more bodies collide. Such a force or acceleration usually has a greater effect than a lower force applied over a proportionally longer time period of time...
causing it to fracture
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
. However, eye witnesses maintained that the girder broke first and the fact that the locomotive
Locomotive
A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
remained on the track showed otherwise.
Publications
It is unfortunate that product failures are not more widely published in the academic literature or trade literature, partly because companies do not want to advertise their problems. However, it then denies others the opportunity to improve product design so as to prevent further accidents. However, a notable exception to the reluctance to publish is the journal Engineering Failure Analysis, which publishes case studies of a wide range of different products, failing under different circumstances. There are also an increasing number of textbooks becoming available.Another notable publication, dealing with failures of buildings, bridges, and other structures, is the Journal of Performance of Constructed Facilities,
which is published by the American Society of Civil Engineers, under the umbrella of its Technical Council on Forensic Engineering.
See also
- Car accidentCar accidentA traffic collision, also known as a traffic accident, motor vehicle collision, motor vehicle accident, car accident, automobile accident, Road Traffic Collision or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other stationary obstruction,...
- Catastrophic failureCatastrophic failureA catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....
- Failure analysisFailure analysisFailure analysis is the process of collecting and analyzing data to determine the cause of a failure. It is an important discipline in many branches of manufacturing industry, such as the electronics industry, where it is a vital tool used in the development of new products and for the improvement...
- Forensic chemistryForensic chemistryForensic chemistry is the application of chemistry to law enforcement or the failure of products or processes. Many different analytical methods may be used to reveal what chemical changes occurred during an incident, and so help reconstruct the sequence of events...
- Forensic electrical engineeringForensic electrical engineeringForensic electrical engineering is a branch of forensic engineering, and is concerned with investigating electrical failures and accidents in a legal context. Many forensic electrical engineering investigations apply to fires suspected to be caused by electrical failures...
- Forensic evidence
- Forensic materials engineeringForensic materials engineeringA branch of Forensic engineering, the subject focuses on the material evidence from crime or accident scenes, seeking defects in those materials which might explain why an accident occurred, or the source of a specific material to identify a criminal...
- Forensic photographyForensic photographyForensic photography, sometimes referred to as forensic imaging or crime scene photography, is the art of producing an accurate reproduction of a crime scene or an accident scene using photography for the benefit of a court or to aid in an investigation. It is part of the process of evidence...
- Forensic polymer engineeringForensic polymer engineeringThe study of failure in polymeric products is called forensic polymer engineering. The topic includes the fracture of plastic products, or any other reason why such a product fails in service, or fails to meet its specification...
- Forensic Science
- FractographyFractographyFractography is the study of fracture surfaces of materials. Fractographic methods are routinely used to determine the cause of failure in engineering structures, especially in product failure and the practice of forensic engineering or failure analysis...
- Stress analysisStress analysisStress analysis is an engineering discipline that determines the stress in materials and structures subjected to static or dynamic forces or loads. A stress analysis is required for the study and design of structures, e.g., tunnels, dams, mechanical parts, and structural frames among others, under...
- Structural analysisStructural analysisStructural analysis is the determination of the effects of loads on physical structures and their components. Structures subject to this type of analysis include all that must withstand loads, such as buildings, bridges, vehicles, machinery, furniture, attire, soil strata, prostheses and...
- Structural failureStructural failureStructural failure refers to loss of the load-carrying capacity of a component or member within a structure or of the structure itself. Structural failure is initiated when the material is stressed to its strength limit, thus causing fracture or excessive deformations...
- Trace evidenceTrace evidenceTrace evidence is evidence that occurs when different objects contact one another. Such materials are often transferred by heat induced by contact friction....
- Vehicular accident reconstructionVehicular accident reconstructionVehicular accident reconstruction is the scientific process of investigating, analyzing, and drawing conclusions about the causes and events during a vehicle collision...