Prediction of environmental stress cracking in plastics with. There are several different polymers that are offered in various pei plastics. Stress cracks or surface crazing near stress concentrators like threads can be a sign of future problems. High performance plastics materials guide tactical sealing. The addition of a surfaceactive chemical, an environmental effect, accelerates this type of failure, thus this mechanism is termed environmental stress cracking esc. Plastic failure through environmental stress cracking. Performance plastics not only uses ultems transparent grades, but. In these applications, chemicals such as isopropanol and lipid solutions can initiate crazesmicrocracks bridged by polymer fibrilsin the plastic and seriously compromise its mechanical integrity.
Glass filled or copolymers extem resin amorphous thermoplastic polyimide tpi superior chemical. Ultem pei stock shapes are inherently flame resistant with low smoke emission. Material displays property retention and resistance to environmental stress cracking when exposed to a wide variety of chemicals. It is a physical process driven by the applied stress but accelerated by. This phenomena, although rare and preventable, is known to occur in many types of. The polymer chains eventually creep toward the pull and deform. Ultem pei stock shapes display property retention and resistance to environmental stress cracking when exposed to a wide variety of chemicals. The standard color of ultem unfilled stock shapes is light amber.
Prevent failure by understanding why plastic parts crack. The chemical simply accelerates the stress cracking. The solution, again the way the plastic sees things, is to reduce the retained molecular. The goal of this article is to provide a framework for evaluating the suitability of a plastic for medical uses in terms of its stress crack behavior. In this mechanism the solvent actually replaces polymer at the surface of the part. The results reported here confirm that environmental stress cracking phenomena in plastics depend on the size and shape of the test liquids molecules as well as their hansen solubility parameters hsp relative to those of the polymer. Sold as plastic sheet and plastic rod in a variety of colors. Prediction of environmental stress cracking in plastics. The presented cases illustrate how the failure analysis process. It is important to note that this data is only of an indicative nature, derived from all sorts of literature related to the chemical resistance of plastics. Unlike most other amorphous thermoplastics, ultem machining resins retain strength and resist stress cracking when exposed to automotive and aircraft fluids, aliphatic hydrocarbons, alcohols, acids, and weak aqueous solutions.
Environmental stress cracking article about environmental. The synergistic effects of the chemical agent and mechanical stresses result in cracking. Ultem stock shapes are inherently flame resistant with low smoke emission. Although the information and statements herein are believed to be accurate, no guarantee of their accuracy is made. When exposed to chemicals, plastic materials may generally react in either of two ways. A materials resistance against this type of failure is called environmental stress cracking resistance escr. The mechanisms of environmental stress cracking pro posed in the literature will be. The results reported here confirm that environmental stress cracking. Its environmental stress and crack resistance make it an excellent plastic for any. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. Reducing environmental stress cracking in plastic parts. Ultem stock shapes display property retention and resistance to environmental stress cracking when exposed to a wide variety of chemicals. A guide to chemical resistance of engineering plastics. Ultem sheet natural interstate plastics plastic sheet.
Ultem resin displays excellent property retention and resistance to environmental stress cracking when exposed to most commercial. This type of cracking typically involves brittle cracking, with little or no ductile drawing of the material from its adjacent failure surfaces. Environmental stress cracking examples from the automotive indsutry jeffrey a. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that. Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in yield point among various polyethylenes. Prediction of environmental stress cracking in plastics with hansen. Environmental stress crack resistance of polyethylene introduction to environmental stress cracking and escr over the past decade, highdensity polyethylene hdpe materials have improved significantly and now meet more stringent performance standards. Environmental stress cracking esc is not the result of the continual battle that the plastics industry has in convincing environmentalists and politicians that. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. Environmental stress cracking the the chemical agent does. Environmental stress cracking esc is not the result of the continual battle that the plastics industry has in convincing environmentalists and politicians that plastics can be the solution to environmental problems and not the cause.
According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical. Environmental stress cracking is involved with some 25% of plastic part failures. Environmental stress cracking of polyvinyl chloride in. Duratron u ultem thermoplastic is high strength at high temperatures, and flame resistant. The chemical agent does not cause direct chemical attack or molecular degradation. Ultem machining sentinel plastics experts in all plastic. With force and time, crazing or stress cracking occurs. When other ultem injection molders lose their cool. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. High stress levels in plastic are a common cause of component field failures. Standard test method for environmental stresscracking of. It is the combination of stress and fluid contact that causes failure to occur much earlier than either component could achieve in isolation, if at all. Esc is a very important mode of plastic component failure.
Since this is responsible for 15% of all failures of plastics components, environmental stress cracking has long been the subject of intensive research. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical strength. Definition of environmental stress cracking esc environmental stress cracking esc in plastics means the failure at about room temperature due to continuously acting external andor internal stresses in the presence of surface active substances known as stress cracking agents such as alcohols, soaps, dyes, agents containing moisture. Diagnose it before it ruins your parts residual stress is an inherent result of plastics manufacturing processes and occurs when molten polymer is cooled and shaped. Environmental stress cracking, often referred to as esc, causes a stressed plastics part to become brittle and crack when in contact with a wide range of fluids that act as stress cracking agents. The potential for environmental stress cracking is of paramount concern when plastics are used in medical device components such as luers and stopcocks. Performance engineering plastics wah lee group south eas asia. Sabic ultem sheet and rod industrial plastic supply, inc. Plastic failure through environmental stress cracking esc, the plastic killer, is a frequent cause of field failures by jeffrey jansen the madison group, madison, wisconsin, usa environmental stress cracking esc is considered a lead ing cause of plastic part failure. Environmental stress cracking is a failure mechanism very similar to slow crack growth in terms of shape. Simultaneous action of stress and strain on plastics in contact with specific fluids causes the onset of cracking and embrittlement of plastic known as environmental stress cracking. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Some performance evaluation tests that once took only days to run now take months with todays. High fill rates results in more molecular orientation.
Injection molded part defects cracks in molded parts. The gate area is an area where the highest fill rates occur. The proper selection of a medical plastic requires a thorough analysis and interpretation of the phenomenon of environmental stress cracking. Its environmental stress and crack resistance make it an excellent plastic for any outdoor condition. Aug 01, 2008 get a handle on stresscracking in hdpe bottles one of the first applications for blow molded hdpe bottles was the replacement of glass for bleach packaging. Environmental stress cracking resistance of polyethylene. Environmental stress cracking is one of the most common causes of unexpected brittle failure of thermoplastic polymers known at present. Solvent stress cracking, which is often incorrectly referred to as environmental stress cracking, can occur in almost any plastic. Pbipei blends can be useful in severe environmental conditions and have good impact resistance, solvent. Plastic stress test protocols connecticut plastics. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused.
Ultem injection molding ultem plastic molding resin. It is the premature embrittlement and subsequent cracking of a plastic. Evaluating environmental stress cracking of medical plastics. Nov, 2012 cracking at the gate cracks that appear near or at the gate location of a molded part are usually caused by molecular orientation. When the solvent diffuses into the polymer, stresses develop because of swelling of the. Environmental stress crack resistance of polyethylene stress crack reagent concentration in the case of the most commonly used stress crack reagent, igepal co630, as the concentration of water in the stress cracking media increases, the faster the esc onset. It is a physical process driven by the applied stress but accelerated by the presence of.
Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. Designing for escr application development material physical properties shrinkage chemical compatibility flame resistance design wall section sharp corners knit lines ribs wall transition tooling. Environmental stress cracking the the chemical agent. Even when exposed to alcohols, acids, solvents, aliphatic hydrocarbons, and automotive and aircraft fluids, ultem retains its strength and resists cracking. Reduce environmental stress cracking esc of your plastic parts by better predicting failure occurrence and implementing adequate prevention measures. In last months article we defined the terms environmental stress cracking and solvent stress cracking, briefly explained the mechanisms involved, and provided a couple of examples of actual case studies. However, it usually occurs in amorphous thermoplastics. It is prone to stress cracking in chlorinated solvents. Astm d1975 16 standard test method for environmental stress. Ultem rod natural interstate plastics plastic sheet. Ultem is one of the most dimensionally stable thermoplastics, predictable and reliable over an extremely broad temperature range. Stress crazing on acrylic surfaces and its causes stress crazing, which appears as an area of tiny microcracks, occasionally shows up in areas on the surface of most thermoplastic sheets. Ultem resin amorphous thermoplastic polyetherimide pei resins long term heat resistance.
Glass filled grades appear tan or greenish in color. This materials isan excellent machining amorphous thermoplastic which possesses a combination of useful characteristics, including high strength at elevated temperatures, high modulus, and broad chemical resistance. Even when exposed to alcohols, acids, solvents, aliphatic hydrocarbons, and automotive and aircraft fluids. How to prevent stress cracking what is stress cracking. Jansen stork technimet new berlin, wisconsin e nvironmental stress cracking esc is a phenomenon in which a plastic resin is degraded by a chemical agent while under stress, and it is the leading cause of plastic component failure.
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