With force and time, crazing or stress cracking occurs. Reducing environmental stress cracking in plastic parts. Environmental stress cracking esc, a brittle failure mode of plastic parts under. Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. Often moisture in the material, weak welding, or inmold stress can result in a dramatically weakened product, shortening the projected lifespan of the workpiece. 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. A guide to chemical resistance of polycarbonate sheet. Environmental stress cracking esc is a premature failure of a polymer exposed to a fluid, under stress which is much less than its yield stress.
Environmental stress cracking examples from the automotive indsutry jeffrey a. Environmental stress cracking esc is the occurrence of cracking a polymer by contact with a liquid or vapor environment, combined with stress. Environmental stress cracking esc is considered a leading cause of plastic part failure. It is a solventinduced failure mode, in which the synergistic effects of the chemical agent and mechanical stresses result in. Based on this, for the purpose of capturing the formation of that radical, we carried out an observation of the phenomenon of envi. Investigations on environmental stress cracking resistance. Despite advances in plastic manufacturing and continuous attempts to make durable, longlasting plastic, the material can still experience failure. Whereas some cracking results from excessive loads, or from thermal or uv degradation, a large percentage of plastic part failure results from a phenomenon termed environmental stress cracking esc, which is the result of an external chemical acting on a plastic part that contains internal stresses. By environmental stress cracking, we understand a failure in which materials in contact with a fluid are subjected to stress. Standard test method for environmental stresscracking of. Evaluating environmental stress cracking of medical plastics.
Polycarbonate is an incredibly useful plastic for applications requiring transparency and high impact resistance. When a part or product fails, the consequences can be severe. Environmental stress cracking may account for around 1530% of all plastic component failures in service. 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. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that can keep us out of trouble with this challenging problem. Re your query on environmental stress cracking of plastics, the corrosion resistance data given out by the manufactures sometimes indicate that a given thermoplastic in a given environment at a given temperature may not be suitable. Plastic failure through environmental stress cracking. 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. If the plastic is under stress, it may also experience environmental stress cracking, which can be defined as the crazing and cracking that may occur when a plastic. 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. Environmental stress crack resistance escr is a vital property required in plastics for its longevity.
Under certain conditions of stress and in the presence of environments such as soaps, wetting agents, oils, or detergents, ethylene plastics. Here, the environmental stress cracking esc is considered as the main cause for the failure of plastics. We postulated that at that time a radical may form. This phenomenon is characterized by the presence of brittle fracture, multiple cracks, smooth morphology. Solvent stress cracking, which is often incorrectly referred to as environmental stress cracking, can occur in almost any plastic. Aggressive exposure of plastics to chemical contaminants to detect instances of environmental stress cracking esc 1, 2. It is the premature embrittlement and subsequent cracking of a plastic. Environmental stress cracking resistance of plastics. Environmental stress cracking esc is the leading cause of plastic components failure. This concept may contribute to environmental stress crazingcracking but is generally believed to be a minor effect in consideration of the overall mechanism particularly where severe stress cracking occurs. The manufacturing process itself is crucial when it comes to preventing plastic failure. When the stress profile within a plastic part is known, adjustments in the process, material, or part design may be. Many experimental works were done before in an effort to predict experimentally the esc potential of a fluid in different polymers. Environmental stress crack resistance of polyethylene.
Some performance evaluation tests that once took only days to run now take months with todays. A materials resistance against this type of failure is called environmental stress cracking resistance escr. 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. 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 is involved with some 25% of plastic part failures.
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. Esc is the occurrence of cracking in a polymer by contact with a liquid or vapour environment and stress. The tensile stress may be applied externally or may simply be a consequence of residual, or moldedin, stresses. At creative mechanisms, we have used polycarbonate in a number of applications across a range of industries. Its the reason you cant put stickers on your motorbike helmet. 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 esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. Therefore, the problem does not show up until a significant amount of product has been shipped. Influencing the environmental stress cracking resistance of. Environmental stress cracking in plastics rj lee group. Pdf stress cracking of polycarbonate exposed to sunscreen. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. Stress cracking is the most common cause of plastic product failure and is particularly difficult to manage since the time frame of this type of failure is typically weeks or months. In this mechanism the solvent actually replaces polymer at the surface of the part. The mechanism of environmental stress cracking esc of amorphous polycarbonate in isopropyl alcohol, ethylene glycol monomethyl ether and methanol.
D541914a standard test method for environmental stress crack resistance escr of threaded plastic closures environmental stress crack resistance threaded plastic closures. Evaluating environmental stress cracking of medical. The escr of polyethylene, one of the most widely used plastic materials, is of particular concern in the plastics industry and is the subject of this investigation. Environmental stress cracking esc is widely regarded as the leading cause of plastic. Chemical resistance chart for plastics an indepth look. Pdf environmental stress cracking is involved with some. Repeated cleanings can cause environmental stress cracking esc that can lead to part failure.
Standard test method for environmental stress crack. Oct 25, 2011 stress cracking is the most common cause of plastic product failure and is particularly difficult to manage since the time frame of this type of failure is typically weeks or months. It is called environmental stress cracking and basically it means that solvents cause the material to crack due to built in stresses in the polycarbonate. Environmental stress cracking environmental resistance. Environmental stress crazing 799 ntetradecane hexane isooctane 1400 1600 600 1200 nhexane 7. Esc is a failure mechanism whereby a plastic resin is effected by a chemical. Environmental stress cracking an overview sciencedirect topics. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids. Environmental stress cracking esc is a welldocumented phenomenon in plasticpolymer components and can occur when a polymer component is exposed to an aggressive chemical agent while under tensile stress, whether residual or applied. Since this is responsible for 15% of all failures of plastics components, environmental stress cracking has long been the subject of intensive research. Investigations on environmental stress cracking resistance of.
How to prevent stress cracking what is stress cracking. The mechanisms of environmental stress cracking proposed in the literature will be discussed in detail. Environmental 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. In environmental stress cracking in plastics, an environmental liquid seeps into the plastic, resulting in swelling, and this causes a crack to occur. Environmental stress crack resistance escr testing of. Environmental stress cracking esc is a welldocumented phenomenon in plastic polymer components and can occur when a polymer component is exposed to an aggressive chemical agent while under tensile stress, whether residual or applied. 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. 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. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused. Therefore, its especially important to identify common types of failure and their underlying causes. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact.
Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. The lenses were injection molded from a polycarbonate resin and. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. The third type of attack is often the most difficult to predict since environmental conditions dictate whether or not the plastic will be affected. This problem is well known and is called environmental stress cracking.
Reduce environmental stress cracking esc of your plastic parts by better predicting failure occurrence and implementing adequate prevention measures. The stress at which esc cracking occurs is often well below the nominal fracture stress of the. Chemical attacks are sometimes considered esc environmental stress cracking when related to vulnerabilities in the plastic s structure. However, it is also extremely sensitive to liquids that come in contact with it and will become weakened and crack. The chemical simply accelerates the stress cracking. Standard test method for environmental stresscracking of ethylene plastics 1. For example, polyethylene, which could hardly be considered an engineering plastic. Environmental stress cracking resistance of polyethylene.
Environmental stress cracking in plastics rj lee group, inc. 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. Often, environmental stress crazing esc is the lifelimiting mode of failure. It is a lighter alternative to glass and a natural uv filter, so it is often used in eyewear. In environmental stress cracking, the presence of an esc agent accelerates the effect of stress on a polymer material. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which. High levels of stress also lower a products impact strength and can contribute to environmental stress cracking and diminished performance at high or cycling temperatures. However, it usually occurs in amorphous thermoplastics. Esc is a very important mode of plastic component failure. Environmental stress cracking an overview sciencedirect. Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials.
It is one of the most common causes of unexpected brittle failure in thermoplastic. Chemical attacks are sometimes considered esc environmental stress cracking when related to vulnerabilities in the plastics structure. Chemical resistance chart for plastics an indepth look at. The presented cases illustrate how the failure analysis process. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. Environmental stresscracking has been found to occur most readily under such. 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. Sabic unveils its new lnp elcres crx pc copolymers that. Esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. The polymer chains eventually creep toward the pull and deform. Smithers provides an overview of environmental stress cracking for polymer materials, and how test programs can help reduce or even prevent failure. Prediction of environmental stress cracking in plastics.
Esc occurs in conjunction with internal and external stresses on a plastic. Environmental stress cracking the the chemical agent does. Environmental stress crack resistance escr testing of plastics. Prediction of environmental stress cracking in plastics with. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present.
Combinations of certain environments, coupled with stress andor strain upon the material, cause stress cracking or crazing of the polycarbonate sheet. Environmental stress cracking the the chemical agent. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than. 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. Environmental stress cracking esc is a welldocumented phenomenon in plasticpolymer components and can occur when a polymer component is exposed. Polycarbonate cracking polymer engineering engtips. It is the premature embrittlement and subsequent cracking of a plastic due to the simultaneous and synergistic action of stress and contact with a chemical agent. Environmental stress cracking the plastic killer researchgate. Our strategy will be to examine, in some detail, the roles of the three critical components of environmental stress cracking. Because the mechanisms of failure for solvent attack and environmental stress cracking are so different, the means of optimizing material parameters are different as well. In the escr test, tensile bars are bent to specific strain levels typically 0.