Instructions for Authors s13

Proceedings in MANUFACTURING SYSTEMS Proceedings in Manufacturing Systems, Vol. 5 (2010), No.

RISK ASSESSMENT IN THE IMPLEMENTATION OF COMPOSITE MATERIALS

Irina PETRESCU1, Constantin ISPAS2, Cristina MOHORA

Abstract: This article aims to identify risks that may arise in using composite materials but also the potential dangers that may occur on human health. The results obtained from risk analysis shows that composite materials can cause serious problems during use, namely: material under the influence of mechanical failure that caused growth and propagation of cracks or detachments. Wear by friction is another destructive process of the composite materials equivalent to rupture or the deformation. Oxidation and / or corrosion are two other processes which lead to progressive and fast degradation of the surface products and so at an advanced wear.

Key words: Risk, Risk theory, Composites, Fissure, Rupture, Wear

1. INTRODUCTION Tel/+4021-402 91 00, Fax:+4021-318 10 01 analysis shows that composite materials can cause In many ways, life is far less risky than in the past, serious problems during use, namely: material under the yet great prominence is given by society to risk and its influence of mechanical failure that caused growth and consequences. Despite technological advances and propagation of cracks or detachments. Wear by friction is growing life expectancy we perceive the world as another destructive process of the composite materials increasingly uncertain and unpredictable. The sense of equivalent to rupture or the deformation. Oxidation and / uncertainty is all pervasive: it's there every time we open or corrosion are two other processes which lead to a newspaper, turn on the television or surf the web, we progressive and fast degradation of the surface products are inundated with images of risk. Yet we cannot avoid and so at an advanced wear. Oxidation at high risk, nor should we. Just imagine a world without it: in temperatures becomes more dangerous, but largely the absence of risk there would be no innovation, no depends on the nature of the matrix and additional reward and no responsibility. Risk is a positive force for material. Corrosion occurs at low and high temperatures growth and success, turning uncertainty and discovery to in the area of contact between components (galvanic an organisation's advantage. corrosion due to electrochemical potential difference In terms of current technological development, raw between the matrix and complementary phase). materials, energy crisis worldwide, and increasing human Other risks that need to be taken into account are aggression towards the environment, led to the those that act on the health and integrity of human development of new materials and of unconventional resources involved in the production process. The main technologies. consequences on using composites is to inhale dust Composite materials are, without doubt, a fascinating particles from processing who may cause problems in the area. Top-level domains (nuclear, military, aerospace and respiratory system. The contact between the powder and others) have boosted research, design and production, eyes may cause eye irritation and when interacting with requiring performance extremely high, which justified the skin, the result is also irritation or dermatita. the fierce competition in these areas. Composite materials have important advantages compared with 2. WHAT IS RISK? traditional materials and bring numerous functional advantages: weight low, mechanical and chemical Risk? Nothing more simple and yet something more resistance, low maintenance cost, freedom and dynamic complex to identify and especially to control. From the design. Wide variety of manufacturing processes, with all dawn of history, the risks were one of the largest and original applications, the problems of optimization most exciting challenges for humanity because of its fabrication process and reduce pollution, are factors that omnipresence in all fields.What is risk? In the acceptance make a composite material the peak area of science in of classical theory of decision, it is identified as an today technology. [1] uncertain element but possible that appears permanent in This article aims to identify risks during processing of the process of humanities activities, whose effects are composite materials but also the potential dangers that damaging and irreversible. If the accepted date dictionary may occur during use. The results obtained from risk defines risk as "exposure to possible loss or damage”, the insurance companies consider this item as" chance or possibility of loss. "In statistical advanced theories risk University "Politehnica" of Bucharest , Machine and Production assessment is given a more elaborate definition of risk: Systems Department, Splaiul Independentei 313, Bucuresti, Cod Postal 060042, ROMANIA "risk reflect variations in the distribution of possible leading to the hypothesis (in fact very pertinent) that outcomes, probability and subjective values”. [2] different decision makers will have different concepts for the same situation.Yet, how can we have in this context, Next, mention several definitions found in the a unified image of the risk, if there are so many different literature. These definitions allow us to understand better approaches on the same concept? The solution comes the notion of risk, to characterize and we can very rigorous in identifying the common elements evaluate.Currently, there is no definition genrally underlying all these definitions, which is uncertainty accepted of the concept of risk, but most definitions (indeterminacy) and loss. Thus we can state that the based on the assumption that risk is a combination of notion of uncertainty is present in all definitions of risk, probability for an frequency and magnitude event in the as validation of its existence will always lead to the consequences of these appearances. Risk is defined by existence of two possible outcomes distincte.We will AFNOR (French association for standardization) as consider an risk event is not affected, if known with "likely to produce an event generally with unfavorable certainty that any context would produce a loss. consequences on the cost or operation delay and that Immediate reality to reveal that virtually no conscious mathematically transpose by the degree of dispersion of process that took place in every industry, uncertainty can possible values around the probable value and an event not be eliminated. In this context it can be concluded the likely to quantify the probability that the final amount fact that risk and uncertainty are found virtually stay within the acceptable”[3]. Another issue is the everywhere, though combined in different proportions. In perception of risk. Remy Gautier mentions that special situations, unpredictable events can cause psychological and psychosocial risk research insist on the fundamantal deviations able to modify the data subjective and differentiated nature of the process. On configuration problem; uncertainty itself becomes a quantifying those set risks out below as „risk potential risk factor. Although present in different measurement is done by non-linearity analysis revealed combinations, risk and uncertainty can not be confused to the utility of money, either by variation of probability between these two concepts, there are some significant distribution of possible gains and losses for each differences, most important of which stipulates that: particular choice”.[4] "while risk can make certain assumptions about events that may occur and the probabilities associated with their Generally, in taking a decision to develop or achieve production, the uncertainty, decision-maker can identify new goals we should consider uncertainty and risk. The all or even any of the possible events to occur and much risk may be associated with danger, uncertainty may be a less to estimate their likelihood .[6] negative component, or a positive component generated by unpredictable state benefits. In this situation, the Risk management is a process of identifying, negative component is associated with risk. Generally, analyzing and systematic reporting of risk factors. It uncertainty refers to doubts that creates an occurrence. involves maximizing the probability and consequences of As i said above, risk in general acceptance, represents a positive events and minimize the probability and danger. consequences for the opposite events in the project objectives. By its very nature, life is intrinsically bounded to the risk. It is generally accepted that any activity involves To be successful, an institution must be ready to solve risk. Risk can not be considered a flaw, a lack of problems of risk management, whenever they occur. A efficiency or of truth, but the very essence of the activity. measure of the seriousness of an institution is on the way Risk is a notion social, economic, political, or natural, to develop procedures for collecting and analyzing whose origin lies in the possibility of future action to information about potential risk. generate losses due to incomplete information or inconsistencies in the decision type of logical reasoning. Key risk management processes are: Risk is what you need to raise anxiety in the market, it is a necessary evil - within certain limitations - and is a  risk management planning - deciding how the risk motivational factor in the dynamism of investment management issues will be approach and planned; activity. Risk is an event occurrence is uncertain and affect the achievement of which enterprise objectives.  risk identification - determining and documenting Gallati consider the risk: "The condition in which the risk factors that could occur in the project; potential for a deviation from the desired situation and planned. Different people do not perceive risks in the  qualitative risk analysis - performing prioritized same manner. The attitude regardind the risk is risk factors approach; frequently described as a stable feature of each individual  quantitative risk analysis - measuring the personalities. Certain issues such as sense of humor, probability and consequences of risk factors and feelings and the way that problems are presented may estimating their implications for project objectives; change the perception of risk issues on them. Must made a distinguish between perception and acceptance the  planning the response to risk factors - the risk”.[5] procedures and techniques development to enhance opportunities and reduce threats to the objectives of Considering all these issues out, we notice that the project; general definitions in the literature for risk varies greatly, 3

 monitoring and controlling risk factors - double torsional strenght, the stiffness is 2.5 times bigger monitoring permanent risk factors, identification of new then steel, high internal damping capacity and superior risk factors, enforce plans for risk reduction, effective resistence to fatigue and corrosion. It is considered that evaluation throughout the entire project life cycle. [2] in use, on the shaft may occur or not overloads (denote them Y or N). We do not know in advance if this overloads will appear, but our experience indicate that their appearance forecast may allow describing this uncertainty in probabilistic terms, say the probability of overload may be P(Y) = 0.3, thus the probability of the shaft not overloaded is equal to P(N) = 0.7. Now let the results set R consist of four elements "excellent", "good", "bad" and "awful" (denote them E, G, B, A), and the mapping M is described as follows:

 M(Y,C)=A, (1) Fig 1. Risk management processes 3. RISK THEORY  M(Y,S)=B, (2)

Risk theory is essentially a branch of probability  M(N,C)=E, (3) theory, devoted to decision-making under probabilistic uncertainty. Basic concepts of the theory are: risk, risk  M(N,S)=G. (4) measure, risk price, and individual attitude to risk. The following picture presents a simplified scheme of Now the decision of choosing making the shaft from decision-making. [7] composites material induces the following probability distribution on the results set:

Tabel 1.

The probability distribution for composite shaft Value Awful Bad Good Excellent Probability 0.3 0 0 0.7

The decision of choosing making the shaft from steel would induce the following distribution:

Tabel 2. Fig.2 Simplified scheme of decision-making The probability distribution for steel shaft Here: S is a set on environment states; Value Awful Bad Good Excellent D is a set of possible decisions; Probability 0 0.3 0.7 0

R is a set of achievable results.

Result is influenced by both decision and environment state. Thus, a mathematical model of the object just described is a mapping M: S x D --> R, that for an environment state s and decision d calculates the result r = M(s,d).

Environment state is usually uncertain. In the framework of risk theory the uncertainty is described by a probabilistic model, that is, by a probability distribution on S. Together with the mapping M this distribution for each decision d from D induces a distribution on R. Thus for each decision there is a probability distribution on R, so making the best decision mean choosing the "best" distribution on R among those available.[8] 3.1. Example Consider the following simple example, a shaft transmission of a composite or steel (so the set of possible decisions D consists of two elements C and S). Composite shaft would be much better because it has a Fig. 3 Cardan shaft composite construction Since the early industrial age, iron and steel were the “heart” of the main industrial sectors progress. While in Making optimal decision means choosing the better from developed countries, already made a tendency to register the two probability distributions. A well known approach long term demand reduction for intensive industrial consists of assigning an "utility" U(r) to each result r, material products, a decline in the use of intensity raw calculating expected (mean) utility u of result of each materials, the low material consumption becomes an decision with subsequent choice of decision that leads to essential element of manufacturing technologies in these greater expected utility. Now let us assign utilities as countries, there is a need for lighter materials, stronger described in the following table: and more sustainable. There is complaint from consumers regarding the high energy embedded in these Tabel 3. materials, but sometimes too high and their prices. Lately the idea has emerged that extend use of composites for The assign utilities new parts in automotive industry is not possible, without Value Utility resorting from high quality reinforced plastics. Awful 0 Bad 2 Composite materials have been designed to replace a Good 5 growing proportion, traditional ferrous and non ferrous Excellent 10 materials, which are characterized by limitations on the performance, procedures for obtaining and processing, gauges, tables, geometric complexity, areas of use costs. Calculating expected utilities brings us Composite materials are materials with anisotropic properties consisting of several components, whose  u(S) = 0.3  2 + 0.7  5 = 4.1, (5) organization and development characteristics allow the use of best parts. From a technical standpoint, the term  u(C) = 0.3  0 + 0.7  10 = 7. (6) refers to composite materials that possess the following attributes: Thus expected utility of composites material shaft is greater than that of steel shaft; so we are choosing  artificially created by combining different composites. ingredients;

Let us look if things change when probability distribution  is a combination of at least two outstanding changes. Let P(Y) = 0.8 and P(N) = 0.2. Calculating materials chemically, which have a distinctive boundary; expected utilities leads to  has properties that no component taking  u(S) = 0.8 2 + 0.2  5 = 2.6, (7) separately can have it.

 u(C) = 0.8  0 + 0.2  10 = 2, (8) The major advantage, essential to composites is that he can achieve modulation properties and thus a very so now we would better choose the steel shaft. large range of materials, use of which it may be extended in almost all fields of technical activity. Practical, In the scheme just described decision is influenced composites consist of a matrix (plastic, ceramics and not only by distribution on S , but by prescribed utility metal) and the reinforcing elements (reinforced), which values as well. The following picture shows how are arranged in matrix in different proportions and utilities of decisions depend on the probability of orientations. Reinforcement gives high strength to overload. composite material and is the centerpiece of taking the load and the matrix material is intended connection Choosing the shaft material 12 between the reinforcing elements and external environment of the load transfer to them. In general, 10 these two phases do not react with one another and are chosen to be inert to each other in terms of uses. 8 Composite materials have many advantages among y t i l i 6 t Composite which stated: U material 4 Steel  low densities compared with metals (eg epoxy resin composites reinforced with silicon, boron and 2 carbon have densities below 2 kg/dm3)

0 0 0.2 0.4 0.6 0.8 1  high tensile (composite called Kevlar, aramid Probability of overload organic polymer fiber has a tensile strength two times Fig. 4. The utility depending on the probability greater than glass);

4. COMPOSITES MATERIALS  expansion coefficient very small compared with metals; 5

 high shock resistance;

 high durability;

 large vibration damping;

 greater safety in operation (rupture of a fiber from a piece of composite primer is not breaking);

 low power consumption and less expensive installation process of obtaining, in relation to metals;

 chemical resistance and high resistance at high temperatures (fibers of Kevlar, Teflon and hyfil up to 500oC, and ceramic fiber-type SiC, Si3N4, and Al2O3 o o between 1400 C and 2000 C).[9] Fig.6. Stratified composite material The aim of this paper is to analyse the risks of using composite material and for these risks to appear there are many factors that influence. In this idea, will present Interface between reinforcement material and matrix major environmental aggressive factors, the polymer has The higher the adhesion between the polymer material a high importance on the physical - mechanical and the matrix, the higher the mechanical strength of the properties of composite material.[10] composite material is. Basically at the polymer

reinforced interface there must be some high cohesion BIOLOGY strengths. This is difficult to accomplished because of FACTORS: differences in chemical structure between the material - Biodegradation that formed the polymer matrix and the reinforced. This produced by mushrooms must be done in a rigorous selection of materials to - Plant species achieve maximum compatibility. There are situations in and animals which the reinforce surface of the material, should be PHYSICAL FACTORS: treated with adhesion promoters agents. Another problem is the difference between the mechanical properties of - temperatures and MECHANICAL polymer matrix and reinforcing materials.[11-13] thermal cycles; FACTORS: - humidity; COMPOSITE - static load Generally, reinforcing material has high tensile strength, - drying, fire; - impact; - UV; MATERIAL - presure; large elastic modulus but low elongation. Polymer matrix - proton and - vibration; has greater flexibility and high elongation at break, but electron radiation; - speed. - voltage ; the tensile strength is lower. High tensile strength - Magnetic field; composite material is the result of the dependence CHEMICAL interface polymer reinforced because at the interface are FACTORS - salt; propagate in generally cracks due to differences in - acids; structure of materials. Due to a large amount of - oils. reinforcing agent and his structure (powder or fibers) may occur many interfaces polymer - reinforced. To achieve a composite with higher properties, the polymer should cover the reinforced surface, and this coverage is required to be uniform. At each point of polymer – reinforced interfaces there must be strong adhesion strength to transfer the effect of external forces from the reinforced into the matrix. If the adhesion is not large enough to show the effect of external forces is manifested cracks at the interface, and consequently degradation of the composite. [14]

The importance of the interface was demonstrated by a simple calculation that determines the number of interfacial area present in a typical laminate. For example considering a square board with 65% polymer reinforced fiberglass, with the side of 305mm and the thickness 25mm, reinforced volume is 1529,31 cm3. If we consider that the fibers are cylindrical and have an average diameter of 0,01mm, interfacial area will be 6.117.244cm2. This area will be covered to achieve Fig.5. Aggressive environmental factors acting on composite maximum properties. [15] materials In most cases it is necessary to improve adherence to matrix polymer reinforcing agent. Thus, it has developed a series of chemical compounds to achieve this goal. Important adhesion agents who serve as interlayer between the polymer matrix and the reinforcing agents, and that may apply to the reinorced surface or mixed with polymer, was demonstrated by many researchers [16-17]. Most adhesion agents are organosiloxani. It was noted that by using these products it is improves strength over 100%. The action mechanism of adhesion agents can be described briefly [18] Fig 7. Fiber rupture in composite material  increase the adhesion forces at the polymer – reinforced ;

 improve flexibility, by their nature being flexible By using bonding agents noted a substantial increase substance; in fracture resistance of composites. When polyester resins increase of over 40% and about 25% epoxy resin.  help eliminate air from the system allowing to Results occur when used as bonding agents in polyester increase surface contact between the polymer and composites is due to increase their adhesion to reinforced. reinforcing material. Epoxy resins have a much better adhesion to reinforcing material, so the breaking strength So to achieve a composite with optimum properties is is higher elongation and compression, in which case the necessary for the polymer adhesion to the reinforcing effect is not spectacular use bonding agents. Improved agent to be great. Thus the contact surface must be full tear epoxy composites has nothing to do with interface and there is the possibility to cover evenly the reinforced conditions, but using bonding agents improves the polymer. To obtain higher strength it is necessary to use composite surface protection. very high adhesion agents. Before discussing the correlation between matrix polymer interface and Composite materials can cause serious problems breaking reinforced composite material, must specify the during use: material under the influence of mechanical amount interfacial tensions that arise from breaking. For failure that caused the emergence, growth and example, if a polyester molding compound reinforced propagation of cracks or detachments. Wear by friction is with glass fibers (50% volume), the elongation strength another destructive process of the composite materials is 344,83MPa. Glass fiber loading is 662,07MPa at break equivalent to rupture or the deformation. Oxidation and / and the polymer matrix when the fracture load is or corrosion are two other processes which lead to 25,17MPa. Tensions arising from polymer interface - progressive and fast degradation of the surface products reinforced include residual stresses and tensions of and so at an advanced wear. Oxidation at high external loading. These tensions were calculated temperatures becomes more dangerous, but largely approximately Broutman [18]. depends on the nature of the matrix and additional material. Corrosion occurs at low and high temperatures Shear strength at the end of the filament is 66,2MPa, in the area of contact between components (galvanic occurring as a result of the elasticity matrix polymer corrosion due to electrochemical potential difference filament which transmits external load is applied between the matrix and complementary phase). compression and elongation of the composite. Radial tensions that are generated in the polymer matrix Other risks that need to be taken into account are actioneza perpendicular to the filament, having a those that act on the health and integrity of human compressor for applying a stretching or elongation when resources involved in the production process. The main applying a compressive loads. Residual stresses have consequences on using composites is to inhale dust values between 19,31MPa and 35,86MPa depending on particles from processing who may cause problems in the the distance between the fibers. Shear stress, the respiratory system. The contact between the powder and application of stretching and compression loads and eyes may cause eye irritation and when interacting with residual stresses are higher than strength, and contribute the skin, the result is also irritation or dermatita.Inhalable significantly to resistance to fracture of the composite. carbon fibres have been suspected to pose similar threats Crack is initiated at the interface and propagate to human health as asbestos fibres. It is well-known that throughout the composite volume before final rupture fibres having a diameter of less than 3 µm might be [19]. Fracture initiation occurs at the contact between inhaled and transported deep into the human respiratory two filaments, the contact angle is sharp. In this case system. Some composite materials use carbon fibres as noted that breakage occurs at a loading of 80% of the structural reinforcement. These fibres do not pose any compressive strength of the composite. risks as such as they are firmly connected to the laminate and surrounded by a polymer matrix. Also, these fibres typically have diameters >6 µm and thus, are not inhalable. However, if the material is exposed to a fire, the carbon material might be oxidized and fractionated 7 and thereby, inhalable fibres might be generated into the [8].http://steconomice.uoradea.ro/anale/volume/20 fire smoke. [20] 05/finante-contabilitate-banci/48.pdf

The capability of carbon fibre-based composite [9]. http://www.utgjiu.ro material to produce dangerous inhalable fibres from [10]. Camelia Cerbu, Ioan Curtu , Tensiunile si deformatiile different combustion scenarios has been investigated. It generate in materialele composite de un mediu agresiv, was found that the risk of fires generating inhalable http://www.utgjiu.ro carbon fibres is related to the surface temperature, the oxygen level and the airflow field close to the material [11]. H.A. Clark, Bonding of Silane Coupling Agents in surface. The temperatures necessary for oxidation of the Reinforcement of Plastics, Modern Plastics, Nov. 1996, p 87. carbon fibre is so high that it is possible that only a [12]. S. Sterman, The Newer Silane Coupling Agents, 20th flashover situation will pose any real danger. Other Conf. SPI Reinforced Plastic Division. possible danger scenarios are highly intense fires (e.g. a liquid fuel fire), or situations where structural damage is [13]. N.V. Trivissiono, The Effect of Glass Finishing Agents on part of the fire scenario. the Strenght of Polyester-Fiberglass Laminates, 12th Conf. SPI Reinforced Plastic Division

[14]. K. Ito, Evaluation of Glass Fiber Surface Treatment in 5. CONCLUSION Fabric-Reinforced Plastics, J. Polymer Sci., 45, 155 .

[15]. B.M. Vanderbilt, Effectiveness of Coupling Agents in DPlastic Materials Reinforcement, Modern Plastics, Nov 1996, As many and varied information they are available to p.79. economic agents, however reluctant and cautious they may be, they will never manage to avoid uncertainty and [16]. S. Sterman, A New Interpretation of the Glass Coupling to eliminate risk entirely. The only solution is knowing Agents Surface Through Use Electronic Michroscopy, 19th the risk, with the aim of the limit, take, and accept, not to Conf. SPI Reinforced Plastic Division. be subject entirely to chance. The aim of this paper was [17]. E.P. Pleuddemann, Evaluation of New Silane Coupling to know the risk of using composite materials and to take Agents for Glass Fiber Reinforced Plastics, 17th Conf. SPI measures to prevent them or at least mitigate the effects Reinforced Plastic Division. they can produce. Although we found that there are various risks using composite materials, namely: the [18]. L.J. Broutman, Glass Resin Joint Strenght and their Effect possibility of occurrence cracks and their propagation on Failure Mechanism in Reinforced Plastics, 22th Conf. SPI material to break, negatives effects on human health due Reinforced Plastic Division. to their high degree of toxicity , yet materials composites have more advantages than disadvantages, and their [19]. L.J. Broutman, Failure Mechanism in Glass Reinforced Plastics Subjected to Staic Compression, Creep and Fatigue, special properties have revolutionized the entire industry 19th Conf. SPI Reinforced Plastic Division. worldwide. [20]. W.D. Bascom, Some Surface Chemical Aspects of Glass Resin Compozites, 20th Conf. SPI Reinforced Plastic Division.

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