Beeinflussung der Korrosionsbeständigkeit von nichtmetallischen Werkstoffen durch Herstellen,Umformen und Fügen

Effects of Production, Forming and Joining on the Corrosion Resistance of Non-metallic Materials The effects of production and processing on the corrosion resistance of parts consisting of thermosetting plastics and thermoplastics are described. The resistance of parts made from glass-reinforced reactive resins can be influenced via their curing and surface quality. High internal stresses in thermoplastic parts, caused by production, forming and welding, lead to stress cracking, which may be considerably accelerated by certain ambient media. Bonded joints between fibres reinforced pipes are often weak points because they are made with fillercontaining cements that may be less resistant to corrosion than the pipe materials. Practical examples illustrate the effects of the factors described on the corrosion resistance of parts made from plastics.     

车灯塑料的环境应力开裂性能研究

用ISO4600规定的球压入法研究了七种常用车灯塑料的耐环境应力开裂性能,得出了这些车灯塑料不宜接触的化学介质环境．实验结果表明,塑料环境应力开裂时间与溶剂的溶解度参数有关,并且还与聚合物的结晶性以及聚合物中填充物的加入有密切的关系。     

Untersuchungen zur Zeitstandfestigkeit von Thermoplast-Rohren unter Chemikalieneinwirkung

Investigations on long term strength of thermoplastic tubes in chemical media . Mechanical long term behaviour of plastics is influenced by environmental media, similar to stress corrosion cracking of metals. Therefore chemical resistance is not to be seen only by immersion tests but has to be found by long term tests under both, mechanical and chemical loading. The paper deals with a test method which shows shortening of the time for rupture of small tube specimens loaded by internal pressure after being filled with the medium. Examples are given for interpretation of results obtained in an international test program.     

Fractography of metals and plastics

Fractography is critical to failure analysis of metals and plastics. Fractography of plastics is a relatively new field with many similarities to metals. Using case histories, various aspects of failure analysis and fractography of metals and plastics are compared and contrasted. Failure modes common to both metals and plastics include ductile overload, brittle fracture, impact, and fatigue. Analogies can also be drawn between stress-corrosion cracking (SCC) of metals and stress cracking of polymers. Other metal/plastic failure analogies include corrosion/chemical aging, dealloying/scission, residual stress/frozen-in stress, and welds/knit lines. Stress raisers, microstructure, material defects, and thermomechanical history play important roles in both types of materials. The key fractographic features for metals and plastics are described in this paper.     

Environmental stress cracking of polyethylene high density (PE‐HD) induced by liquid media – Validation and verification of the full‐notch creep test (FNCT)

The full‐notch creep test (FNCT) is widely used to characterize the slow crack growth (SCG) behavior of polyolefin materials in “inert” media as well as effects of environmental stress cracking (ESC) in which the medium has decisive influence on damage mechanism and time to failure. The test is of greatest importance for pipe and blow molding types of polyethylene, high density (PE‐HD). Usually the full‐notch creep test is applied as a standardized testing method (ISO 16770) using a few universal liquid media, such as solutions of Arkopal N 100. In our study, selected relevant polyethylene, high density materials are investigated also in real media – practical formulations as well as representative pure chemicals – and influences of temperature and geometry of specimen and notch are explicitly addressed. Furthermore, the investigations comprise also the environmental stress cracking behavior of polyethylene, high density in media that are sorbed to a significant extent – examples are diesel and biodiesel – based on comparison with samples previously saturated with those media. Thus, also the underlying diffusion controlled sorption process has to be assessed before. The investigations were performed using a full‐notch creep testing device with 12 individual sub‐stations, each equipped with individual electronic stress and temperature control and continuous online monitoring of the specimen elongation.     

Möglichkeiten der Geruchsmessung und ‐minderung bei Naturfaserverbunden

Possibilities of Odour Measurement and Reduction of Natural Fibre Plastics The critical attitude of the German public concerning environmental questions has also invaded the world of odours. The evaluation and reduction of odours when using plastic materials has gained increasing significance in the last years. The packaging industry that produces wrapping materials for food and other consumables was the first to test for odours. During the last years the automobile industry has also shown increased interest in pinpointing and measuring odours, not only because of the increased usage of natural fibre reinforced plastics in car interiors, but also because of the general increase of concern over clean air. Natural fibre reinforced plastics, besides having advantages compared to glass‐ and carbon reinforced materials (mechanical properties/weight, CO₂‐equilibrium) also have properties that limit their application possibilities. Emissions and unpleasant odours at certain temperature and humidity conditions are of concern. To determine the origin of odour in bonded materials the single component, production step or their combination causing it has to be found. To achieve odour neutrality in plastics is difficult since production methods or additives can only be determined through prolonged testing and where the human nose is still more important than all the physical electronic measuring methods. The origin of odours and their importance for the well being and health of the population is questioned and forces not only the plastics industry to react. The is why both, plastics‐ and automobile industries are trying to react to the tendencies of the market place and it is the goal of the auto industry to deliver the most odour‐neutral new car.     

Spannungsrißkorrosion in hochreinem Wasser von 3½ % NiCrMoV-Vergütungsstählen für Dampfturbinen-Scheiben und -Wellen

Stress Corrosion Cracking in High Purity Water of 3½ % NiCrMoV – Quenched and Tempered Steel for Steam Turbine Discs and Shafts In recent years intergranular stress corrosion cracking has occured world-wide in the shrink-fitted discs of low pressure turbine rotors made of low alloy steels. Only in a few cases steam impurities such as NaOH, Na₂CO₃, Na₂SO₄, H₂S, or NaCl, which initiate SCC, could be found. The stress corrosion cracking behaviour of the turbine disc steel 26 NiCrMoV 14 5 with a yield strength of approx. 850 N/mm² was examined under special corrosion conditions. Gaseous and other impurities of the water, which lead to higher conductivity can initiate stress corosion cracks and increase the stress corrosion crack velocity insignificant. Stress corrosion crack initiation can be prevented by shifting the pH-value and the free corrosion potential in the region of passivity. Unfavourable crevice conditions must be avoided. Solutions are shown, how to prevent stress corrosion cracking of steam turbine discs.     

Über den Einfluß der Probengeometrie auf die Rißausbreitungsgeschwindigkeit bei Spannungsrißkorrosionsversuchen

The influence of specimen geometry on stress corrosion cracking rates The fracture mechanics characterization of stress corrosion cracking phenomena established the quantitative relation between the stress field around the crack front and the stress corrosion cracking rates. In order to apply the results successfully in structural design, the influence of specimen geometry and test conditions have to be eliminated or minimized. Great experimental efforts are applied worldwide to develop such a testing procedure. The following work is directed to some of the effects resulting from specimen geometry, such as the numerical equations used to obtain the stress-intensity factors, the specimen thickness and crack length.     

Zusammenwirken von Spannungsrißkorrosion und Ermüdung bei der Schwingungsrißkorrosion eines hochfesten Stahles

Conjoint Action of Stress Corrosion Cracking and Fatigue on Corrosion Fatigue of a High Strength Steel The corrosion fatigue characteristics of a high strength, martensitic steel in 0.5 n NaCl solution is investigated with regard to the fatigue and stress corrosion cracking behaviour of the material. Test parameters are stress ratio and frequency, testing is carried out with fracture mechanics methods, the crack surfaces are examined fractographically. An analysis of the results reveals that corrosion fatigue in high strength steel is caused by fatigue or by stress corrosion cracking, depending on the kinetics of the two processes. Fatigue and stress corrosion cracking do not act cumulative or additive. Instead, the kinetically faster process causes crack advance. The crack growth characteristics are interpreted with respect to the fractographic appearance of the crack surfaces. Corrosion fatigue cracks propagate either intergranular relative to the prior austenite grain boundaries as stress corrosion cracks do or transgranular like fatigue cracks, depending on the crack growth rates of the two processes. Fatigue and stress corrosion cracking do not interact, at least in a measurable degree, because of the different crack path of the two fracture processes. Results can be assessed quantitatively with the “process competition model”.     

Plastics in automobiles at SITEV '81

In the March 1981 edition of Materials in Engineering (P149) D. Charlesworth ‘Potential use for plastics in Automobiles’, reviewed in terms of materials properties and processing methods the advantages and limitations of plastics in comparison with metals. In order to convince car makers of the potential of plastics, materials suppliers and component manufacturers develop prototype parts which are publicly displayed, often for the first time, at motor shows. The most important of these shows is the International Exhibition of Suppliers to the Vehicle Industry (SITEV). SITEV '81 took place in Geneva and the more significant new applications of plastics to automobile components are reviewed and their likelihood of adaption by the automotive industry assessed in this article by Dr. N.A. Waterman who is a consultant on materials selection to the plastics and automotive industries.     

The surface cracking of glassy polymers under a sliding spherical indenter

Glassy polymers crack under a sliding hard spherical indenter in a way that is observed in other brittle materials. A series of curved cracks concave to the wake of the indenter are formed and these can penetrate to a depth of a few hundredths of a millimetre. With polystyrene the additional stress imposed by sliding reduces the critical load to fracture under normal loading conditions by 95% and the presence of an active environment, methanol, reduced the critical fracture load for sliding by 83%. Other glassy polymers which are generally considered tough, cracked in the presence of agents which could promote environmental stress cracking. The stress necessary to cause cracking and the crack size obeyed laws pertaining to fracture under elastic stress conditions. Although the flaws observed are referred to as cracks it is recognized that they could possibly be crazes. The introduction of surface damage in the form of cracks or crazes is important practically, since the inadvertent scratching or abrasion of the polymer surfaces may introduce flaws which under normally acceptable stress-environmental conditions could lead to failure. It is also noted that the flaws are detrimental to the polymer's optical properties.     

取向玻璃纤维增强塑料的应力腐蚀开裂研究

应用断裂力学的理论和方法对±30°、±45°、±60°三种取向玻璃纤维增强塑料的应力腐蚀开裂行为进行了研究,并与单向玻璃纤维增强塑料的应力腐蚀开裂行为进行了比较。结果表明,纤维取向对玻璃纤维增强塑料的应力腐蚀行为有很大影响。三种取向玻璃纤维增强塑料的耐应力腐蚀性能强弱顺序为:±30°、±45°、±60°玻璃纤维增强塑料。与单向玻璃纤维增强塑料相比,三种取向玻璃纤维增强塑料有更高的应力腐蚀临界载荷值,低于该载荷,可以认为在可接受的时间范围内不会发生应力腐蚀。进一步的讨论证实纤维/基体界面在取向玻璃纤维增强塑料的应力腐蚀中起着重要作用。随外加载荷的变化,取向玻璃纤维增强塑料与单向玻璃纤维增强塑料的应力腐蚀裂纹扩展机理不同。      

TWINTEX纤维增强塑料的应力腐蚀开裂

研究了TWINTEX纤维增强塑料在酸中的应力腐蚀,并与玻璃纤维增强塑料的应力腐蚀进行了比较.结果表明,TWINTEX纤维增强塑料具有比玻璃纤维增强塑料好得多的耐应力腐蚀性能,而且这种好的耐应力腐蚀性主要表现在长的裂纹孕育期.聚丙烯纤维良好的耐蚀性是造成长的裂纹孕育期的主要原因.外加载荷的变化对TWINTEX纤维增强塑料的应力腐蚀裂纹扩展速率的影响不如其对玻璃纤维增强塑料的应力腐蚀裂纹扩展速率的影响显著.     

Cracking in bolted SMC components

Recent developments in the substitution of plastics for metal components have led to a requirement for further information on the applicability of existing mechanical fastenings to these newer materials.The generic group of glass reinforced thermoset plastics known as ‘polyester moulding compounds’ has been found to be suitable for many replacement components, particularly in the automotive industry, but these materials are subject to cracking under certain loading conditions. The present work uses a simulated bolt loading technique to relate material thickness, bolt diameter, and support configuration to a limiting sustainable load. Acoustic emission methods are also used to relate the onset of cracking to the support conditions and the ultimate load.The conclusions suggest that, for the material studied, positioning of the fixing hole at least two hole diameters from the material edge and use of a material thickness/bolt diameter ratio $\text{≥3}$, should result in the equivalent mild steel bolt failing before cracking is initiated or ultimate composite failure occurs.     

High temperature acidic stress corrosion of glass fibre composites: Part I Effect of fibre type

The stress corrosion characteristics of uniaxial glass fibre reinforced thermosetting resin composites have been examined in hydrochloric acid at 80°C. A simple technique based on linear elastic fracture mechanics (LEFM) is presented for characterizing crack growth in these materials subjected to hostile acidic environments. The environmental stress corrosion cracking is investigated both for different types of resin and different types of glass fibre reinforcements. Two matrices were used: DERAKANE* 411-45 epoxy vinyl ester resin (based on Bisphenol-A epoxy resin) and DERAKANE 470-30 epoxy vinyl ester resin (based on epoxidized novolac resin). Two glass fibre types were employed: standard E-glass fibre and ECRGLAS®, a special type of E-glass with superior acid resistance. Model experiments using a modified double cantilever beam test with static loading have been carried out on unidirectional composite specimens in 1 M hydrochloric acid solution at 80°C. The rate of crack growth in the specimen depends on the applied stress, the temperature and the environment. Consequently, the lifetime of a component or structure made from glass fibre reinforced plastics (GRP) subjected to stress corrosion conditions, could be predicted provided the dependence of crack growth rate on stress intensity at the crack tip is known. Scanning electron microscope studies of the specimen fracture surfaces have identified the characteristic failure mechanisms. The most important finding of this work is that the selection of DERAKANE epoxy vinyl ester resins reinforced with ECRGLAS® fibre exhibited superior resistance to crack growth at 80°C compared to similar E-glass reinforced composites at room temperatures.     

Spannungsrißkorrosion in hochreinem Wasser von 3–3 ½% NiCrMoV-Vergütungsstählen für Dampfturbinen-Scheiben und -Wellen. Teil I

SCC in High Parity Water In recent years intergranular stress corrosion cracking has occured world-wide in the shrink-fitted discs of low pressure turbine rotors made of low alloy steels. Only in a few cases steam impurities such as NaOH, Na₂CO₃, Na₂SO₄, H₂S or Nacl, which initiate SCC, could be found. To clarify the SCC-behaviour experiments on turbine disc steels with different chemical compositions an yield strength were performed in high purity water. The results show, that chemical composition has no effect on the crack initiation. Under high purity water conditions no crack initiation due to stress corrosion cracking is observed on the steel with a yield strength of 850 N/mm². On the steel with a yield strength of 1250 N/mm² which is not used in service, crack initiation occurs in pure water. But if sharp cracks already exist, crack propagation occurs in both cases. The investigations showed, that stress corrosion cracking of turbine discs can be prevented by a good water chemistry with a cation conductivity less than 0.2 μS/cm (μmho/cm).     

Mechanische Verträglichkeit bei Verbundwerkstoffen – Naßkorrosion

Mechanical compatibility of metallic composites . Corrosion in aqueous media. As a main condition for corrosion in aqueous media between components of a composite material, both components have to be touched by an invironmental wed atmosphere or of a fluid. If this condition is given contact corrosion can take place with any composite, independent of the mechanical compatibility of the components. Crevice corrosion is possible too if mechanical incompatibility (or extern loads) causes cracks between the components; stress corrosion cracking is possible as well. Stainless steel vires, for instance, can not reinforce the composit if attached by SCC. The other kinds of corrosion mostly dammage the matrix, which also reduces properties of the composit. Examples are given of possible kinds of corrosion for some fiber reinforced metallic composites and for metal laminates.     

A numerical model for the time‐dependent cracking of cementitious materials

A unified finite element formulation is presented for the analysis of the time‐dependent cracking of cementitious materials. The rate‐type constitutive law incorporates linear visco‐elasticity and continuum plasticity. The former accounts for the bulk creep via a Maxwell chain, while the latter describes crack initiation and propagation via a softening, anisotropic Rankine yield criterion. The rate dependence of bond ruptures leading to fracture is accounted for by considering the viscosity of the cracking process. This contribution to the cracking resistance also regularises the localisation process. It is demonstrated how other important phenomena in cementitious materials, such as stress‐dependent hygral and thermal shrinkage, can be incorporated into the computational framework. Copyright © 2001 John Wiley & Sons, Ltd.     

Oberflächenfunktionalisierung von Kunststoffoptik

Surface Functionalization of Polymer Optics Transparent plastics have been used for optical applications with growing demand. This development is accompanied by a desire for extended surface functionalities like antireflection and hardening. Coating processes well established for glass optics cannot be applied in most cases. A manifold of polymer materials with different chemical surface states require special coating deposition parameters. In the first part of the tutorial the main plastic materials are introduced and their properties which are important for the vacuum deposition processes will be discussed.     

Amplitude distribution acoustic emission signatures of unidirectional fibre composite hybrid materials

The failure processes in fibre-reinforced materials can be arranged in order of ascending energies as matrix crazing, interfacial delamination and fibre fracture. In glass fibre-reinforced plastics, delamination plays a significant part in the failure process. In carbon fibre-reinforced plastics, failure normally occurs by catastrophic fibre fracture with very little acoustic activity before the event. When two composites are combined within a single matrix to produce a fibre composite hybrid material, it is expected that a mixture of failure modes will occur, although this will be dependent on stress and strain levels. Acoustic emissions are the sounds generated by materials under stress: in practice, the amplitude of the acoustic emission signal is most commonly used as a measure of energy. Thus if a histogram of the number of acoustic events within a specific range of energies is formed, then a characteristic series of ‘signatures’ can be expected for each type of composite. The results of amplitude distribution acoustic emission tests are reported in this paper for unidirectional carbon fibre with glass fibre hybrid reinforced plastics, tested to failure in bending.