Fracture mechanics testing for environmental stress cracking in thermoplastics. Environmental stress crack resistance of polyethylene. Environmental stress crack resistance, escr, of several candidate plastics for instrument panels was studied using both constant load and constant strain methods. Often we tend to group all the problems into the environmental category, but in reality most of the field problems we see have to do with solvent stress cracking. 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. 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. The environmental stress crazing and cracking in polystyrene under high pressure.
Esc is a very important mode of plastic component failure. Prediction of environmental stress cracking in plastics. Unfortunately, a number of applications for impact modified polymers is in areas where there is a high potential to contact with oily or fatty. 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. Prediction of environmental stress cracking in plastics with. Environmental stress cracking esc of plastics caused by. Thus allowed us to predict the risk of esc as a function of the filler content for different stresscracking agents without performing extensive tests. Environmental stress cracking is involved with some 25% of plastic part failures. It is associated with the phenomenon of crazing and solvent plasticization of the polymer. For a comparison of different amorphous polymerbased nanocomposites at a given nanosio 2 particle.
Conditions of stress and strain that accelerate environmental stress cracking are one of the major goals of the research. Polypropylene is a lowcost thermoplastic elastomer, which consists of aliphatic hydrocarbon chains and is mainly used in packaging industries owing to its high fatigue resistance, good chemical and environmental stress cracking resistance, low density, and ease of processing. Relevant phenomena most commonly include thermal stresses, physical ageing, frozenin strains and molecular orientation. Environmental stress cracking the the chemical agent does.
Environmental stress cracking in impact polystyrene wiley online. 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. Engineering and manufacturing science and technology, general cracking materials research failure mode and effects analysis methods strains and stresses stress relaxation materials stress relieving materials stresses materials thermoplastics environmental aspects mechanical. Processing conditions have a strong effect on the final mechanical properties of products made of polymeric materials. Environmental stress cracking escr is the formation of cracks in a part when. Environmental stress cracking resistance tester escr.
The stress at which esc cracking occurs is often well below the nominal fracture stress of the. The bent strip test is a constant strain test, but polyethylene relaxes when strained. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known. Standard test method for environmental stress crack. Environmental stress cracking can take place through continuous crack growth or via a stepwise progressive mechanism of cracking and arrest, depending on the molecular structure of the plastic, the composition of the chemical agent, the level of stress, and other environmental conditions.
Fracture mechanics testing for environmental stress cracking in. Similarly, for both bonding methods, reduce stress, either by creative joint design or distributing the stress over a larger bond area. Special polystyrene grades and their particular properties highgloss polystyrene ps 454 c polystyrene grade with increased environmental stress cracking resistance ps escrimotm 14 15 styrolux and its characteristic properties mechanical properties optical properties thermal properties electrical properties rheology chemical resistance. Fourier transform infrared difference spectroscopy has been utilized to measure the concentration of trace amounts of fluid penetrating the polymer during deformation. Environmental stress cracking resistance of polyethylene. D541914a standard test method for environmental stress crack resistance escr of threaded plastic closures environmental stress crack resistance threaded plastic closures. This grade has an improved environmental stress crack resistance in comparison.
Styron xtech polystyrene resin platform i s an advanced technology driving innovation for numerous polystyrene applications in the home appliances, packaging, and building and construction markets. Pdf effect of processing on the environmental stress cracking. The stressstrain behavior of polystyrene is dependent on the temperature and on the deformation rate. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. 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. It was shown that esc in impact polystyrene is controlled by the transport of the aggressive liquid through a preestablished dry craze structure where capillary pressure is the driving force. Environmental stress cracking of polypropylene springerlink. The presented cases illustrate how the failure analysis process.
Method and device for determining the environmental stress. Environmental stress cracking an overview sciencedirect topics. 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. For example, high impact polystyrene hips, copolymers of. It was shown that esc in impact polystyrene is controlled by the transport of the aggressive liquid through a pre. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. As a service to our customers we are providing this early version of the manuscript. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids. In general this problem falls into two subcategories. Since this is responsible for 15% of all failures of plastics components, environmental stress cracking has long been the subject of intensive research. The environmental stresscrazing and cracking in polystyrene under. Polystyrene, high impact ps hips highimpact polystyrenes are used for products requiring higher impact resistance and increased environmental stress cracking resistance compared to general purpose polystyrene.
Polycarbonateabs blends demonstrated significantly better escr properties than the. Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials. Influence of small rubber particles on the environmental stress. Nov 22, 2000 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. Please redirect your searches to the new ads modern form or the classic form. It is essential for the understanding of part failure processes fatigue, overload, or environmental stress cracking especially in parts used for structural applications, especially in low. By environmental stress cracking, we understand a failure in which materials in contact with a fluid are subjected to stress. The environmental stresscrazing and cracking in polystyrene under high pressure. Presto group provides a wide range of polystyrene testing instruments. On the effect of nanofillers on the environmental stress. Environmental stresscracking has been found to occur most readily under such. Difference between polypropylene and polycarbonate. It is known that physical ageing for polystyrene at room temperature is limited and, therefore, a significant difference in volumetric state would arise only in samples subjected to very different cooling rates. Environmental stress cracking esc measurements for various impact polystyrenes were performed using a constant load technique with the specimens in contact with a 5050 solution of cotton seed oil and oleic acid.
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. Environmental stress cracking resistance tester is a unique test cabinet designed to detect the change. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. The problem lies, in part, in the definition of stress cracking. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. Environmental stress cracking esc of acrylonitrilebutadienestyrene abs copolymer caused by two kinds of nonionic surfactants was studied by edge crack tension ect tests and the morphology at the crack tip was studied with transmission electron microscope tem. Environmental stress cracking esc measurements for var ious impact polystyrenes were performed using a constant load technique with the specimens in. Environmental stress cracking occurs because of a process of local plasticization due to the diffusion of an active degradant, craze formation, and its growth under stress. Ductile brittle transition temperature plastics properties. Ampa plastics also manufactures a modified form of hips known as escrhips, or environmental stress crack resistant hips. The polymer chains eventually creep toward the pull and deform.
Environmental stress cracking behavior aging behavior resistance to highenergy radiation. In this work, two different highimpact polystyrenes, processed by. Improved environmental stress crack resistance high impact polystyrene, polystyrene impact 8260 is a high impact polystyrene for extrusion and injection applications. Us5543461a environmental stress crack resistance of hips. Environmental stress cracking examples from the automotive indsutry jeffrey a.
Generalpurpose polystyrene gpps highimpact polystyrene. Extensional and fractural properties of concentrated. Highimpact polystyrene hips is a rubbermodified polystyrene that is significantly harder and more impactresistant than general purpose polystyrene. Method for determining the environmental stress cracking. The environmental stresscrazing and cracking in polystyrene. Methods for evaluating environmental stress cracking have also been used in. Evaluating environmental stress cracking of medical. Influence of small rubber particles on the environmental stress cracking of high impact polystyrene article in journal of applied polymer science 12. For specific cases in which the effect of an environment on polyethylene has not been documented, testing is required to identify any possible environmental stress cracking effect.
Hips is opaque and is often used in vacuum cleaner components, toys and household items. 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. When bonding pvc to polystyrene, the plasticizers in the pvc can leach straight through the adhesive and attack the polystyrene. Evaluating environmental stress cracking of medical plastics. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that. Outstanding compressive strength and high water flow rate characterize this premium. Method for determining the environmental stress cracking resistance. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents. How to prevent stress cracking what is stress cracking. Improved rigidity and environmental stress cracking resistance escr advanced downgauging with a cost savings of up to 10%. Investigations on environmental stress cracking resistance. The extensional and fractural properties were measured for concentrated solutions of polystyrene over wide ranges of extension rate and temperature. Fluids conventionally classified as inert exert a strong stress crazing and cracking effect on certain amorphous polymers when they are deformed in tension under pressure.
We are the supplier of polystyrene testing instruments all across the globe. Influence of small rubber particles on the environmental stress cracking of high impact polystyrene. Influence of small rubber particles on the environmental. Generalpurpose polystyrene gpps highimpact polystyrene hips. Introduction polystyrene ps toughness may be greatly improved incorporating a dispersed rubber phase, usually polybutadiene pb, via insitu polymerization, yielding the so.
On the mechanism of pressureinduced environmental stress. The environmental stress crack resistance of polycarbonate. Environmental stress cracking in impact polystyrene, polymer. Sep 01, 2016 read effect of processing on the environmental stress cracking resistance of highimpact polystyrene, polymer testing on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Read effect of processing on the environmental stress cracking resistance of highimpact polystyrene, polymer testing on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. It does not crack, break or shatter when being installed or handled roughly.
High impact polystyrene hips and other impact modified styrenic polymers such as abs and mbs tend to suffer from environmental stress cracking. Effect of processing on the environmental stress cracking. Plastic failure through environmental stress cracking. Standard test method for environmental stresscracking of. Such an effect is known as environmental stress cracking or environmental stress fracture. Environmental stress cracking an overview sciencedirect. With force and time, crazing or stress cracking occurs. Investigations on environmental stress cracking resistance of. Environmental stress cracking in impact polystyrene bubeck.
Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. Environmental stress cracking of poly3hydroxibutyrate. Environmental stress cracking esc is one of the most important causes of polymer premature failure, occurring when a combination of mechanical load and an aggressive fluid is applied. Plastics will exhibit environmental stress cracking when exposed to an aggressive chemical environment if and only if a tensile stress is present. 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. 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 cracking in impact polystyrene. For example, high impact polystyrene hips, copolymers of acrylonitrile butadiene and styrene abs, and high impact polyvinyl chlorides are sensitive to stresscracking in the presence of oils. At moderate stress levels just above the critical stress for environmental cracking, there is an apparent incubation time for the dry craze formation. This stress relaxation allows testing to run without failure for very long periods 1,500 hours. Effect of processing on the environmental stress cracking resistance. The addition of a surfaceactive chemical, an environmental effect, accelerates this type of failure, thus this mechanism is termed environmental stress cracking esc. 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.
Polystyrene parts dipped in kerosene, for example, will craze quickly in stressed areas. This is a pdf file of an unedited manuscript that has been accepted for publication. May 16, 1989 for example, high impact polystyrene hips, copolymers of acrylonitrile butadiene and styrene abs, and high impact polyvinyl chlorides are sensitive to stress cracking in the presence of oils. The stress strain behavior of polystyrene is dependent on the temperature and on the deformation rate. Engineering and manufacturing science and technology, general cracking materials research failure mode and effects analysis methods strains and stresses stress relaxation materials stress relieving materials stresses materials thermoplastics environmental aspects. Escr hips is less susceptible to environmental stress cracking than hips.
1513 96 392 1303 1369 211 782 829 1069 418 1438 1319 1612 1340 1375 634 856 200 1307 802 861 54 1145 1023 1374 377 567 1208 1269 554 1179 1007 1157 209 522 1166 563