Chapter 1 Introduction-Importance of definition

1.1 Definition of basic terminologies related to reliability engineering

-Reliability, failure, safety and so on-

The issue of definition, like as definition of technical terminology in science and technology or problem definition in engineering design, is very important.

It is because the essence of object or problem is identified according to its definition and in turn, its identified essence would provide relevant methods for developing theories or solving the problem.

If a problem is ill-defined, it always leads to wrong solution.

Thinking:

1. What is the definition of ‘length’?

2. What is the definition of ‘time’?

3. What is the definition of ‘force, particularly external force’?

Length is what rules measure. Time is what clocks measure.

Definition by Isaac Newton in Principia published in 1686, written in Latin,

“A force (an external force) is the action (actio) applied to a body in order to change the state of the body of being at rest or of moving uniformly straight forward.”

In Wikipedia,

“A force is any influence that causes an object to undergo a certain change, either concerning its movement, direction, or geometrical construction.”

Author’s definition: “A force is the action to change the state of a body.”

The change of the state of a body means motion and deformation.

1.1.1 Reliability

There are many variations of the definition of reliability.

One is in BS 47781971 as “Reliability is the probability that a component, equipment, or system will perform a required function under the operating conditions encountered for a stated period of time.”

The other is “Reliability is the probability that a component or system will perform a required function for a given period of time when used under stated operating conditions.”

Another is “Reliability is the probability of a device performing its function over a specified period of time and under specified operating conditions.”

Here we use the following definition:

“Reliability is the probability that a product, component or system will perform a required function over a given (specified or stated) period of time under specified conditions.”

Reliability is expressed mathematically because it is defined by the probability.

The terminology is known to be introduced during World War II in USA, in relation to failures and life predictions of electronic equipment.

1.1.2 Failure

A state of loss of reliability, that is, a state that (when) a product, component or system can not perform a required function.

Thinking: What is fracture?

A phenomenon that a body separates into more than two parts.

An other rigorous definition exists in terms of fracture mechanics.

Fracture does not always lead to failure, and failure can occur without fracture.

1.1.3 Safety

The term “safety” is apt to be confused with reliability.

What does “Being safe” mean?

It means “not harmful to human being” or “do not damage to human being.”

On the other hand, “dangerous or risky” means “possibly harmful to human being” or “possibly do damage to human being.”

The damage here includes all the one not only related to life but also to robbery or investment as an economic activity.

Safety is the concept related to the possibility of damage and is essentially probabilistic concept.

Safety is the term expressing the degree of being safe and is generally evaluated by the risk including probabilistic property as shown below.

There are various definitions of risk as follows:

Risk = (probability of the event) x (the severity of the consequences)

= (probability of the accident occurring) x (expected loss in case of the accident)

Or

Risk = (probability of damage occurrence) x (the size (or amount) of the damage)

We use the last simple one.

Even if the value of risk is same, for example, in case that

(high probability of occurrence) x (small damage) = (low probability of occurrence) x (large damage), the perception of risk (recognition of danger or feeling of riskiness) may be different, depending on the individual.

Thinking: Perception of risk

1. The use of cars for ordinary life and the nuclear power plant

2. Other examples?

X-ray examination for a medical[physical／health] examination (or a medical inspection) versus use of computer or mobile phone (electromagnetic wave)

There is other definition related to mechanical safety in the standard ISO/IEC Guide51 as

“Being safe is the state being free from unacceptable risk” or “freedom from unacceptable risk.”

This means that we recognize safety when the risk is acceptable even if it is not zero.

The important is that reliability and safety are clearly different things.

Even if reliability is secured, it doesn’t always mean to guarantee (ensure) safety, but if reliability is lost, it causes the problems of safety.

For example, think of reliably operating machine without any safety devices.

1.1.4 Safety factor

In mechanical engineering, the safety factor is well used to prevent failures of structures and members and consequently to secure their safety.

The safety factor is usually defined as

Safety factor = Strength of material / allowable stress

The strength of material and allowable stress are single definite characteristic values, respectively, and the values represent mean properties of them.

Therefore, the safety factor has no probabilistic property.

Basically, the safety factor cannot treat safety being probabilistic

It is a serious drawback inherent to the safety factor and is one of the reasons why we need to learn reliability engineering

In the recent, the concept of safety factor considering probabilistic characteristics of material strength and load have been introduced and used, which will be described in other chapter.

1.2 Intrinsic nature of engineering and problems of reliability and safety

Through searching the most fitting definition for engineering, we will comprehend the intrinsic nature of engineering and look into its relation to the problems of reliability and safety.

1.2.1 Definition and compositions of engineering

1. Definition of engineering

You can find various definitions of engineering, for example, in internet websites.

A typical example is the definition by ABET(Accreditation Board for Engineering and Technology):

Engineering is the profession in which a knowledge of the mathematical and natural sciences gained by study, experience, and practice is applied with judgment to develop ways to utilize, economically, the materials and forces of nature for the benefit of mankind.

All other definitions are more or less similar to the above.

None of them seems to be satisfying.

Why?

From any definition available, we can never anticipate the inevitable, negative aspects of the progress of engineering and its possible adverse effects or side effects now well pointed out. Further, any current definition of engineering can’t provide any insight into reliability and safety.

Here is introduced a new definition of engineering, by which we can anticipate both positive and negative effects of the progress of engineering:

Engineering is the discipline that realizes what human being or human society requires, wishes, wants or desires, whether material or immaterial, formed or formless, hardware or software.

The first (main) purpose of engineering is to actually realize what be required, be wanted or desired.

The theories for its realization are just secondary. But it doesn’t mean that the theory is not important for engineering. It means that the first priority is the realization and the rigorousness of theory may be neglected frequently.

Engineering is often compared with science.

What is the difference between engineering and science?

Science is somewhat easy to define.

The definition of science: The discipline that interprets natural phenomena, and clarifies and establishes natural laws.

Its first purpose is understanding existing phenomena, and application of theories is secondary.

2. Composition of engineering

Engineering consists of design and manufacturing (production).

Design and manufacturing (production) can be defined as follows:

Design is to plan concretely the process of realization of the purpose of engineering.

Manufacturing (or production) is to make the object along the plan established in the design process.

There may be other definitions.

From the definition and composition of engineering described above, you may find that art is very similar to engineering. However, art and engineering are essentially different from each other. Comparison of engineering with art may make the intrinsic nature of engineering more clear.

Thinking: Engineering and art - their similarities and differences

The process is just the same for engineering and art.

The differences: One is the way how the motive or purpose or need is given,

the other is the evaluation of the product or work .

Engineering

Pure art

Need

to produce what ordinary people want.

be given by an artist himself

Evaluation

If ordinary people have no will to buy the product with economic burden, that is, with money, the product has no any value.

There is good expression by David G. Ullman: “remember”. What you design is what you make is what you sell.

Self-contentment (self-satisfaction) of the artist.

It is not interest of the artist if his work can be accepted or is of high economic value.

But as the artist also must eat to live and needs money for it, the economic value of work of art can’t be neglected. In the real world, the art has, more or less, the same aspects of engineering.

1.2.2 Problems induced by the progress of engineering and prevention measures

1. The root cause (origin) of reliability-and-safety problems ceaselessly occurring

At present that engineering and science have made enormous progress, we must be free from any accident and problem related to reliability and safety. Because we can think that any accident and problem can be avoided or prevented in advance by the power of engineering and science. Unfortunately, it is not true.

Despite of tremendous progress of engineering and science, many accidents and problems ceaselessly still occur. Why?

It appears to come from the intrinsic nature of engineering.

The most importance of engineering is fulfillment of requirements or realization of desire and the theories on the way are secondary.

This leads to the following serious problem. That is, it happens that the primary purpose, namely, realization of desire becomes possible even when all related things are not clarified sufficiently.

In other words, realization of human desire (the progress of engineering) precedes clarification of natural laws (the progress of science).

It’s the very problem and the origin of reliability-and-safety problems.

Examples:

1. Environmental problems

2. Livestock engineering and mad cow disease (BSE- bovine spongiform encephalopathy)

3. Bioengineering problems

4. Genetic engineering problems

5. Problems caused by the progress of information technology

6. Human desire and disease and illness-AIDS(acquired immune deficiency syndrome)

2. Trend of progress of engineering and characteristics of present society, and problems of safety and reliability

Aspect of progress of engineering

The progress of engineering will be made, based on its intrinsic nature, that is, to realize what be required, wanted or desired by human beings and human societies.

And its aspect will be determined by the features of the present human society, and in turn, the progress of engineering changes the human society.

The progress of engineering and the human society interact with each other.

It is like ‘we want something and something is realized and then its realization changes us.’

Remarkable characteristics of present society:

The rate of increase of human desire is terribly higher compared with the past.

The word ‘desire’ includes evil, immoral meaning.

Human beings become greedier and greedier.

Trend of progress of engineering

Size, capacity and efficiency are on the increase.

Influenced by the characteristics of the present society, the direction of progress of engineering is that everything becomes bigger and bigger, its capacity becomes larger and larger, its efficiency becomes higher and higher.

And extreme, ultra, hyper technologies are required.

Example:

(Ultra) cryogenic, ultrafine, super-speed, super-conductivity, hypersonic, hypermarket.

In addition, owing to the change of value judgment, the past paradigm, concentration and uniformity, shifts to new one, diversity, identity and individualization.

The problems of safety and reliability in the present society

Such aspects of progress of engineering influence reliability and safety of all things.

A safety accident in the present may lead to a full-scale and fatal one, causing huge losses of both life and property.

Under the currently diverse and individualized state or conditions, every phenomenon may become so complicated that its clarification and anticipation will be very difficult. We may not expect high reliability for anything.

Thinking this way, we may be living in an uneasy, restless, insecure, risky and dangerous society.

3. Prevention measures for various unfavorable side effects induced by the progress of engineering

1) Fundamental prevention measures

Thinking the inherent features of engineering as described up to now, engineering can be said to be connected closely and directly to the true nature of mankind, or human fate or destiny that persues desire everlastingly.

Consequently, to prevent unanticipated (unexpected) side effects from the progress of engineering from the root, we should suppress the true nature of mankind as far as possible and not let the realization of human desire go ahead of clarification (elucidation) of natural laws.

However, criteria of the elucidation of natural laws are not definitely established or unknown yet. So we may say that the realization of human desire must not be against provision of nature.

For the purpose, ethics and religion seem to exist and be helpful.

Think this way, human sciences and religions are found to be very important also from the view of engineering.

However, their utilities for solving the basic problems due to engineering are very limited and may be practically negligible.

Thinking the nature of enginering, as the progress of science is difficult to go ahead of the progress of engineering, we had better think it impossible to prevent from the root the side effects from the progress of engineering.

Thinking: Utility and limitations of religion

2) Precaution method

As described in the above, there seems no perfect prevention against the side effects due to the progress of engineering. Despite of it, it is possible at least to keep safety from the side effects due to the progress of engineering.

It is one of the most important, basic duties of engineers to develop proper safety precautions.

As a safety precaution, the folowing Heinrich’s Law or Heinrich’s accident angle (pyramid) will be very helpful and useful for considering safety issues.

Heinrich’s Law or Heinrich’s accident angle (pyramid)

Herbert William Heinrich (born 1886) surveyed the approximate 50,000 accidents that occurred in 1920s and published his book “Industrial Accident Prevention, A Scientific Approach” in 1931 and found the socalled Heinrch’s Law or Heinrich’s accident triangle (pyramid) as follows:

For every accident that causes a major injury, there are 29 accidents that cause minor injuries and 300 accidents that cause no injuries.

In other expresstion:

If a fatal or serious accident occurs, there are 29 accidents, and 300 potential incidents which contain high possibility causing injuries.

In another expression:

If an accident occurs, there are 29 incidents which do not lead to the accident, and 300 irregularities which do not lead to the incident, and more than several thousands unsafe acts and states may exist.

Heinrch’s Law can be illustrated in a form of triangle as Fig. 1.2.1 and the triangle is called Heinrich’s accident triangle (pyramid).

Fig. 1.2.1 Heinrich’s accident triangle (pyramid)

Heinrich’s accident triangle has the 300-29-1 ratios.

The significance of Heinrich’s accident triangle

As one accident follows 29 incidents which follow 300 irregularities, paying attention seriously to the irregularities, if only one among 300 ones, and then preparing safety precaution can prevent fatal accidents.

As Heinrich’s study was made in 1930s, it may be doubtful in the recent.

Interestingly, the study of failure which has lately attracted considerable attention in Japan shows similar results that when a big failure occurred, there were about 300 irregularities (so-called near misses) in advance.

Here the meaning of near miss is an event that did not lead to failure, but had the potential to fail.

By utilizing the concept of Heinrich’s accident triangle well, we may always prevent accidents and this means it is not so difficult to secure safety.

1.3 Brief outline of the history of reliability engineering

The history of reliability engineering is well described in the book, Reliability-Based Design by S.S. Rao, McGraw-Hill, 1992, pp.15-16.

Reliability engineering is a discipline established in USA in the 1950s, based on reliability theories developed in relation to failure problems of electronic systems designed in the early 1940s during World War II. In the above book, it was described that during World War II, more than 50 percent of airborne equipment and 50 percent of the spare parts and equipment in storage was damaged or became unserviceable. To solve these problems, The USA Air Force, Navy and Army began studies independently in 1950 and 1951. In 1952, the Department of Defense (DOD) established the Advisory Group on the Reliability of Electronic Equipment (AGREE) and AGREE published its first report on reliability in 1957.

The most important conclusion in the report is that reliability testing must be made in the development of new systems to detect the design defects and correct them at an early stage before production. The report was accepted by DOD and later became a military standard, MIL-STD-781: Reliability Demonstration-Exponential Distribution. The report was also adopted by NASA.

Through these processes, reliability engineering can be said to be established and contributes to the design, development and production of electronic systems.

For more details, refer to the above book by Rao.

1.4 Safety of products in the present and product liability law (PL law)

Using or relying on many products of engineering, we are living comvenient and comfortable lives in the present. However there are many accompanying problems. One of them is safety- or damage-related one.

The more products we use, the higher becomes the possibility that we suffer damage due to product defects.

The bigger, more complex and more advanced the products become, the bigger and more serious the damage is when any problem arises with products.

So, users or consumers must select safe products to buy and use them, considering well these situations. For it, reliable, somewhat professional information may be needed.

However, it is difficult for consumers to acquire professional detailed information on products manufactured by currently advanced technologies and even if they can acquire, it is difficult yet to understand the information.

Consequently, it is usual for consumers to purchase products using available information provided by manufacturers or sellers, e.g. advertisements or product brochures. Therefore, there is a limit to what consumers themselves judge safety of products practically.

Besides, if there occurs any problem with products, consumers will try to claim responsibility of manufcturers for damage. Unfortunately, owing to civil law, consumers have to verify manufacturer’s mistakes or product defects.

It is almost impossible, because most of current products are manufactured through highly complicated manufacturing processes using very advanced technologies.

Consumers don’t know such processes and technologies.

Considering these situations, the product liability law (PL Law) is originally made to protect consumers against damage caused by product defects and to make the manufacturers take responsibility for it.

PL Law can be thought to be originated and developed in America where the contract system is the basis of society. The essence of the law is to protect the rights of consumers having no direct contract with manufacturers.

PL Law was established in USA in 1960s, and has been legislated in Europe from 1985, and was enforced in China in 1993, in Japan in 1995.

In Korea, the law was enacted in 2000 and enforced in 2002.

Parcularly, Japan and Korea had a very negative attitude to PL law, because the law might have the effect to weaken their competitiveness in the world market.

PL law causes to raise the production cost, leading to weak competitiveness in the world market. So, the developed countries including USA having PL law strongly demand the other countries having no PL law to legislate the law.

Korean PL law is as follows:

From www.kplc.or.kr

製造物責任法(영문)  PRODUCT LIABILITY ACT

   Act No. 6109, Jan. 12, 2000

Article 1 (Purpose)

The purpose of this Act is to protect consumers against damage caused by defective products, and contribute to the safety of the citizen's life and the sound development of the national economy by regulating the liability of manufacturers, etc. for damages caused by the defectiveness of their products.

Article 2 (Definitions)

The definitions of terms used in this Act shall be as follows:

1.The term "product" means all movables, industrially manufactured or processed, even though incorporated into another movable or into an immovable; and

2.The term "defect" means the defect of any product in manufacturing, design or expression falling under any of the following items or the lack of  safety that the product ordinarily should provide: and

(a)The term "defect in manufacturing" means the lack of safety caused by manufacturing or processing of any product deviating from the originally intended design, regardless of whether the manufacturer faithfully performs the duty of care and diligence with respect to the manufacturing or processing;

(b)The term "defect in design" means the lack of safety caused by the failure of the manufacturer to adopt a reasonable alternative design in a situation  that   any damage or risk caused by the product would otherwise be reduced or prevented; and

(c)The term "defect in expression" means conditions that a manufacturer fails to give reasonable explanations, instructions, warnings and other indications on the product, while there occurs any such damage or risk caused by the product that would otherwise be reduced or prevented;

3.The term "manufacturer" means a person falling under any of the following items:

(a)A person who is engaged in a business of manufacturing, processing or importing any product; and

(b)A person who  presents himself as any person falling under item (a) by putting his name, firm name, trademark or any other distinguishable feature(hereinafter referred to as "his name, etc.") on the products, or a person who puts his name, etc. on the product in a manner mistakable for any person falling under item (a).

Article 3 (Product Liability)

(1) A manufacturer shall be liable for either damage of death or personal injuries, or damage to any item of property (other than the defective product itself) which is suffered by any person, due to a defect of the product.

(2) With respect to any product the manufacturer of which can not be identified, a person who, for profit, supplies it in a form of sale or lease, etc. shall be liable for damage referred to in paragraph (1), if, in spite that he knows or would be able to know the identity of the manufacturer or the person who has supplied it to himself, he fails to inform any injured person or his legal representative of said identity within a reasonable period.

Article 4 (Exemptions)

(1) Where a person who is liable for damage in accordance with the provisions of Article 3 proves the fact falling under any of the following subparagraphs, he shall be exempted from such liability:

1.that the manufacturer did not supply the product;

2. that the state of scientific or technical knowledge at the time when the manufacturer supplied the product was not such as to enable the existence of the defect to be discovered;

3.that the defect  is due to compliance of the product with any Act or subordinate statute at the time when the manufacturer supplied it; and

4.that, in case of raw materials or components, the defect is attributable to the design of the product in which any raw materials or components have been fitted or to the instructions concerning manufacturing given by the manufacturer of the product using them.

(2) Where, in spite that he knows or would be able to know the existence of any defect of the product after it has been supplied, the person who is liable for damage under the provisions of Article 3 fails to take appropriate measures to prevent the damage caused by the defect from occurring, he shall not enjoy any exemption referred to in paragraph (1) 2 through 4.

Article 5 (Joint and Several Liability)

Where not less than two persons are liable for the same damage, they shall be liable jointly and severally.

Article 6 (Restrictions on Special Agreement Concerning Exemption)

Any special agreement intended to exclude or limit any liability for damage under this Act shall be null and void: Provided, That this shall not apply to the case where a person who is supplied with any product only used for his own business concludes said special agreement with respect to damage to his business property caused by the product.

Article 7 (Time Limitations, etc.)

(1) The right for damage under this Act shall be extinguished by prescription if the injured person or his legal representative does not exercise their rights within three years from the date on which the damage and the person liable therefor under the provisions of Article 3 have come to the knowledge of either of them.

(2) The right for damage under this Act shall be exercised within 10 years from the date on which a manufacturer supplies a product causing damage: Provided, That with respect to damage caused by any substances which are accumulated in human's physical body and, in turn, hurt his heath, or any other damage the symptoms of which appear after a lapse of a certain latent period, the aforesaid period shall be reckoned from the date on which the damage occurs actually.

Article 8 (Application of Civil Act)

Matters concerning any liability for damages caused by the defect in products shall be governed by the Civil Act except as otherwise provided for in this Act.

ADDENDA

(1) (Enforcement Date) This Act shall enter into force on July 1, 2002.

(2) (Applicable Cases) This Act shall apply to products supplied by a manufacturer on or after the enforcement date of this Act.

The most important things of the law are three kinds of defects clearly defined in the law.

1. Defect in manufacturing

2. Defect in design

3. Defect in expression

The meaning of defect in design is very significant. It requires to design the product using the currently most advanced and best technologies.

- 13 -

300

1

29

사고

(accident)

중대

사고

(fatal or serious accident)

사고

(accident)

잠재적

사고

(potential incidents)

사건

(incident)

이상

(irregularity)

300

1

29

사고

(accident)

중대

사고

(fatal or serious accident)

사고

(accident)

잠재적

사고

(potential incidents)

사건

(incident)

이상

(irregularity)