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This research investigates the durability of large-format 3D-printed thermoplastic composite material systems under environmental exposure conditions of moisture and freeze–thaw. Durability was evaluated for two bio-based composite material systems, namely wood-fiber-reinforced semi-crystalline polylactic acid (WF/PLA) and wood-fiber-reinforced amorphous polylactic acid (WF/aPLA), and one conventionally used synthetic material system, namely short-carbon-fiber-reinforced acrylonitrile butadiene styrene (CF/ABS). The moisture absorption, coefficient of moisture expansion, and reduction of relevant mechanical properties—flexural strength and flexural modulus—after accelerated exposure were experimentally characterized. The results showed that the large-format 3D-printed parts made from bio-based thermoplastic polymer composites, compared to conventional polymer composites, were more susceptible to moisture and freeze–thaw exposure, with higher moisture absorption and greater reductions in mechanical properties. [ABSTRACT FROM AUTHOR]

Controller Area Network (CAN-bus) is a default solution for digital control in machinery. The CAN-bus structure uses connector components to extend cabling and join subsystems. The connectors are IP-classified, so they tolerate humidity and particle ingress. Ingress protection also provides durability against other stress factors. Usually, connectors are exposed to multiple stress factors, but the stress levels are durable. In mining applications, however, stress levels can be high, and other factors become significant, so IP classification does not necessarily indicate sufficient durability. Tailored testing can be used to identify suitable components for a specific purpose. In this study, the actual stress factors of an underground mine drill were used in tailored tests. The results showed significant differences in reliability between connector models with the same IP code. The ranking of the components varied depending on the stress factors used. This highlights the importance of using actual operating conditions when evaluating reliability. [ABSTRACT FROM AUTHOR]

This research investigates the durability of large-format 3D-printed thermoplastic composite material systems under environmental exposure conditions of moisture and freeze–thaw. Durability was evaluated for two bio-based composite material systems, namely wood-fiber-reinforced semi-crystalline polylactic acid (WF/PLA) and wood-fiber-reinforced amorphous polylactic acid (WF/aPLA), and one conventionally used synthetic material system, namely short-carbon-fiber-reinforced acrylonitrile butadiene styrene (CF/ABS). The moisture absorption, coefficient of moisture expansion, and reduction of relevant mechanical properties—flexural strength and flexural modulus—after accelerated exposure were experimentally characterized. The results showed that the large-format 3D-printed parts made from bio-based thermoplastic polymer composites, compared to conventional polymer composites, were more susceptible to moisture and freeze–thaw exposure, with higher moisture absorption and greater reductions in mechanical properties.

Herein, electroluminescence (EL) and thermal imaging are used to examine p–i–n metal halide perovskite (MHP) photovoltaic (PV) mini‐modules (MA0.6FA0.4PbI3, 20 cells, 78 cm2) before and after indoor‐accelerated stress testing or outdoor deployment. Distinct spatial patterns in the EL images emerge, which depend on the external stress conditions experienced by the mini‐module. Imaging results highlight a distribution of dark speckle features that dominate after UV stress, attributed to widespread interfacial contact degradation. Lateral intensity gradients across cells dominate after thermal cycling (TC) stress, attributed to current crowding near scribe defects. While current–voltage analysis alone does not give full insight on the degradation process, this study shows that distinct degradation modes can be further defined by multimodal electro‐optical imaging (i.e., EL combined with photoluminescence and dark lock‐in thermography). Neither UV exposure nor TC‐accelerated stress testing alone replicates the same degradation signatures observed after outdoor deployment, suggesting that multiple degradation modes occur under concurrent stressors outdoors. Spatial characterization of degradation modes in MHP PV mini‐modules before and after accelerated stress testing lays the groundwork for developing targeted accelerated stress testing procedures through comparison with outdoor aging. [ABSTRACT FROM AUTHOR]

Combined‐accelerated stress testing (C‐AST) is developed to establish the durability of photovoltaic (PV) products, including for degradation modes that are not a priori known or examined in standardized tests. C‐AST aims to comprehensively represent the sample, stress factors, and their combinations using levels at the statistical tails of the natural environment. Acceleration factors for relevant climate sequences within the C‐AST cycle with respect to the Florida USA climate are estimated for selected degradation mechanisms. It is found that for degradation of the outer backsheet polymer layer, the acceleration factor of the tropical climate sequence (the longest of the climate sequences) is f (T, G) = 17.3 with ultraviolet photodegradation; for polyethylene terephthalate hydrolysis (backsheets), f (T, RH) = 426; for electrochemical corrosion (PV cell), f (I) = 14.1; and for PbSn solder fatigue f (ΔT, r (T)) = 17.3. Here, T is the module temperature, G is the broadband spectrum irradiance on the plane of array of the module, RH is the relative humidity on the module surface, I is the leakage current through the module packaging, and r(T), the number of temperature reversals. The methods discussed herein are generally applicable for evaluating acceleration factors in other accelerated test methods. [ABSTRACT FROM AUTHOR]

The current understanding of the carbonation and the prediction of the carbonation rate of alkali-activated concretes is complicated inter alia by the wide range of binder chemistries used and testing conditions adopted. To overcome some of the limitations of individual studies and to identify general correlations between mix design parameters and carbonation resistance, the RILEM TC 281-CCC 'Carbonation of Concrete with Supplementary Cementitious Materials' Working Group 6 compiled and analysed carbonation data for alkali-activated concretes and mortars from the literature. For comparison purposes, data for blended Portland cement-based concretes with a high percentage of SCMs (≥ 66% of the binder) were also included in the database. The analysis indicates that water/CaO ratio and water/binder ratio exert an influence on the carbonation resistance of alkali-activated concretes; however, these parameters are not good indicators of the carbonation resistance when considered individually. A better indicator of the carbonation resistance of alkali-activated concretes under conditions approximating natural carbonation appears to be their water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio, where the subscript 'eq' indicates an equivalent amount based on molar masses. Nevertheless, this ratio can serve as approximate indicator at best, as other parameters also affect the carbonation resistance of alkali-activated concretes. In addition, the analysis of the database points to peculiarities of accelerated tests using elevated CO2 concentrations for low-Ca alkali-activated concretes, indicating that even at the relatively modest concentration of 1% CO2, accelerated testing may lead to inaccurate predictions of the carbonation resistance under natural exposure conditions. [ABSTRACT FROM AUTHOR]

Polymers and polymer composites are negatively impacted by environmental ageing, reducing their service lifetimes. The uncertainty of the material interaction with the environment compromises their superior strength and stiffness. Validation of new composite materials and structures often involves lengthy and expensive testing programs. Therefore, modelling is an affordable alternative that can partly replace extensive testing and thus reduce validation costs. Durability prediction models are often subject to conflicting requirements of versatility and minimum experimental efforts required for their validation. Based on physical observations of composite macroproperties, engineering and phenomenological models provide manageable representations of complex mechanistic models. This review offers a systematised overview of the state-of-the-art models and accelerated testing methodologies for predicting the long-term mechanical performance of polymers and polymer composites. Accelerated testing methods for predicting static, creep, and fatig ue lifetime of various polymers and polymer composites under environmental factors’ single or coupled influence are overviewed. Service lifetimes are predicted by means of degradation rate models, superposition principles, and parametrisation techniques. This review is a continuation of the authors’ work on modelling environmental ageing of polymer composites: the first part of the review covered multiscale and modular modelling methods of environmental degradation. The present work is focused on modelling engineering mechanical properties.

The articles provides the results of the research on the development of the load condition mode selection for acceler-ated testing of the hydraulic system pipelines durability, taking into account the results of zero loading technique providing the adequacy to the actual process of leading to fatigue cracks and material destruction.

• Coupled effects of temperature and water on viscoelastic properties of epoxy nanocomposites. • New methodology for constructing master curves from DMTA temperature scans. • Comparison of master curves and shift factors determined by different methods. • High reinforcement efficiency of nanocomposites maintained after hydrothermal aging. • Modelling time and temperature dependences of storage moduli. Graphene-based fillers are promising candidates for improving the long-term dimensional stability of structural epoxy resins. The development of reliable accelerated test methods is critical to predicting their durability. Herein, the viscoelastic behaviour of the industrial-grade amine-epoxy and corresponding nanocomposites with modified graphene oxide (up to 1.72 wt%) is studied using dynamic mechanical thermal analysis (DMTA) in both temperature and frequency sweep modes. Time-temperature (TTSP), time-water ageing (TWSP), and coupled superposition principles (TTWSP) are used to predict the long-term storage moduli of nanocomposites. The temperature and water shift functions, determined by curve shifting, agree well with the Arrhenius calculations based on data from independent tests. A methodology for constructing master curves from DMTA temperature scans is developed, and the results are well correlated with the predictions made from traditional isothermal multifrequency test data. The temperature and time dependences of the storage moduli are well fitted by known relaxation models, and their parameters are analysed in terms of the filler and water-ageing effects. The results can be applied in the development of the material model and the prediction of macromechanical properties and the service lifetime, which are relevant to examined epoxy/GO composites and other water-sensitive glassy polymers. [ABSTRACT FROM AUTHOR]

The single most reliable indicator of a material’s durability is its performance in long-term tests, which cannot always be carried out due to a limited time budget. The second option is to perform some kind of accelerated durability tests. The aim of the work described in this article was to develop a method for the accelerated durability testing of binders. It was decided that the Arrhenius equation approach and the theory of chemical reaction kinetics would be applied in this case. The degradation process has been simplified to a single quantifiable parameter, which became compressive strength. A model hydraulic binder based on fluidised bed combustion ash (FBC ash) was chosen as the test subject for the development of the method. The model binder and its hydration products were tested by high-temperature X-ray diffraction analysis. The main hydration product of this binder was ettringite. Due to the thermodynamic instability of this mineral, it was possible to verify the proposed method via long term testing. In order to accelerate the chemical reactions in the binder, four combinations of two temperatures (65 and 85°C) and two different relative humidities (14 and 100%) were used. The upper temperature limit was chosen because of the results of the high-temperature x-ray testing of the ettringite’s decomposition. The calculation formulae for the accelerated durability tests were derived on the basis of data regarding the decrease in compressive strength under the conditions imposed by the four above-mentioned combinations. The mineralogical composition of the binder after degradation was also described. The final degradation product was gypsum under dry conditions and monosulphate under wet conditions. The validity of the method and formula was subsequently verified by means of long-term testing. A very good correspondence between the calculated and real values was achieved. The deviation of these values did not exceed 5 %. The designed and verified method does not also consider the influence of other effects, for instance, chemical corrosion or corrosion caused by frost-thaw cycles. However, this method could be a supplementary tool applicable to the study of degradation processes and the estimation of a binder´s durability as well.

Solid oxide fuel cell (SOFC) applications require lifetimes of several years on the system level. A big challenge is to demonstrate such exceptionally long lifetimes in ongoing R&D projects. Accelerated or compressed testing are alternative methods to obtain this. Activities in this area have been carried out without arriving at a generally accepted methodology. This is mainly due to the complexity of degradation mechanisms on the single SOFC components as function of operating parameters. In this study, we present a detailed analysis of approx. 180 durability tests regarding degradation of single SOFC components as function of operating conditions. Electrochemical impedance data were collected on the fresh and long-term tested SOFCs and used to de-convolute the individual losses of single SOFC cell components - electrolyte, cathode and anode. The main findings include a time-dependent effect on degradation rates and the domination of anode degradation for the evaluated cell types and operating conditions. Specifically, the steam content as determined by fuel inlet composition, current density and fuel utilization was identified as major parameter, more important than for example operating temperature. The obtained knowledge is adopted to identify optimal operation profiles in order to acquire accelerated testing for lifetime investigation of SOFCs. [ABSTRACT FROM AUTHOR]

The following study was focused on developing the technology for the evaluation of industrial felt when reliability test among industrial felt is critical. As such, the intentions are to secure reliability of the products, to be used actively for inspecting the reliability of new innovative products, and to help increase quality. The research placed industrial felt in an even more strenuous condition that's different from the actual conditions they are normally used under in order to accelerate the potential for failure. Therefore, the results of the study have confirmed that an accelerated testing criteria conducted under a 30 day period was a good proxy for a year-long usage condition. Additionally, the results show that the old product's strength is only about 50 % of the new product, which is a considerable difference. The reasons for such degradation are due to the reduction in coherence between fabrics which causes destruction in the fibrous tissue which in turn causes a reduction in strength values. Consequently, this study attempts to evaluate the performance and quality of the felt in order to establish a relationship between lifespan and performance. With this, the research deems possible that the process can be applied on the evaluation of the durability life of industrial felt products. [ABSTRACT FROM AUTHOR]

The bond behavior between FRP composites and masonry substrate plays an important role in the performance of externally bonded reinforced masonry structures. Therefore, monitoring the bond quality during the application and subsequent service life of a structure is of crucial importance for execution control and structural health monitoring. The bond quality can change during the service life of the structure due to environmental conditions. Local detachments may occur at the FRP/substrate interface, affecting the bond performance to a large extent. Therefore, the use of expedite and efficient non-destructive techniques for assessment of the bond quality and monitoring FRP delamination is of much interest. Active infrared thermography (IR) technique was used in this study for assessing the bond quality in environmentally degraded FRP-strengthened masonry elements. The applicability and accuracy of the adopted method was initially validated by localization and size quantification of artificially embedded defects in FRP-strengthened brick specimens. Then, the method was used for investigating the appearance and progression of FRP delaminations due to environmental conditions. GFRP-strengthened brick specimens were exposed to accelerated hygrothermal ageing tests and inspected periodically with the IR camera. The results showed environmental exposure may produce large progressive FRP delaminations. [ABSTRACT FROM AUTHOR]

Polymers and polymer composites are negatively impacted by environmental ageing, reducing their service lifetimes. The uncertainty of the material interaction with the environment compromises their superior strength and stiffness. Validation of new composite materials and structures often involves lengthy and expensive testing programs. Therefore, modelling is an affordable alternative that can partly replace extensive testing and thus reduce validation costs. Durability prediction models are often subject to conflicting requirements of versatility and minimum experimental efforts required for their validation. Based on physical observations of composite macroproperties, engineering and phenomenological models provide manageable representations of complex mechanistic models. This review offers a systematised overview of the state-of-the-art models and accelerated testing methodologies for predicting the long-term mechanical performance of polymers and polymer composites. Accelerated testing methods for predicting static, creep, and fatig ue lifetime of various polymers and polymer composites under environmental factors' single or coupled influence are overviewed. Service lifetimes are predicted by means of degradation rate models, superposition principles, and parametrisation techniques. This review is a continuation of the authors' work on modelling environmental ageing of polymer composites: the first part of the review covered multiscale and modular modelling methods of environmental degradation. The present work is focused on modelling engineering mechanical properties. [ABSTRACT FROM AUTHOR]

A new accelerated weathering protocol has been developed which closely replicates the performance of automotive and aerospace coating systems exposed in South Florida. IR spectroscopy was used to verify that the chemical composition changes that occurred during accelerated weathering in devices with a glass filter that produced a high fidelity reproduction of sunlight's UV spectrum matched those that occurred during natural weathering. Gravimetric water absorption measurements were used to tune the volume of water absorption during accelerated weathering to match that which occurred during natural weathering in South Florida. The frequency of water exposure was then scaled to the appropriate UV dose. A variety of coating systems were used to verify the correlation between the physical failures observed in the accelerated weathering protocol and natural weathering in South Florida. The new accelerated weathering protocol correctly reproduced gloss loss, delamination, cracking, blistering, and good performance in a variety of diverse coating systems. For automotive basecoat/clearcoat paint systems, the new weathering protocol shows significant acceleration over both Florida and previous accelerated weathering tests. For monocoat aerospace systems, the new weathering protocol showed less acceleration than for automotive coatings, but was still an improvement over previous accelerated tests and was faster than Florida exposure. [ABSTRACT FROM AUTHOR]

Blended cement pastes are currently used for encapsulation of low level and intermediate level nuclear waste in the UK. However, there is still little information on the long-term durability of those mixes to some chemical attacks. Accelerated testing may predict the long-term durability or at least help the selection of more durable formulations. In this work, blended blastfurnace slag (BFS)/Portland cement (OPC) pastes containing 60, 75 and 90% BFS and pulverised fuel ash (PFA)/OPC pastes with 40, 55 and 75% PFA were cured at 20 and 60°C for 90 days then submitted to natural and accelerated carbonation (5% CO). The effects of the curing temperature as well as the OPC replacement level on the carbonation ratio are presented. Results showed a good correlation between natural and accelerated carbonation for the pastes studied. Carbonation was found to be governed by the amount of calcium hydroxide available in the mixes before the process started. [ABSTRACT FROM AUTHOR]

We have developed a semi-empirical model capable of quantitatively estimating delamination rates (DRs) of adhesive bonds upon exposure to cathodic environments. The equations used in this model are derived from physical considerations that account for variables which influence the DRs: cathodic voltage (implicitly current density), temperature and peel stress (utilizing strain energy release rate, G, as a fracture mechanics parameter). In the model equations, the constants are determined by fitting these equations to experimentally collected delamination data. Nomograms are developed that can be easily consulted in order to determine DRs under a multitude of cathodic polarization, temperature, and strain energy release rate, G. This semiempirical model can serve as a first-order predictor of cathodic delamination rates of adhesive bonds under a variety of cathodic conditions (including some which are highly accelerated). [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an overview of some of the key challenges and issues that need to be overcome in the area of performance and durability to achieve commercial-viable PEM fuel cell technology 1 [1] http://www.ballard.com/be_informed/fuel_cell_technology/roadmap. . While there has been significant progress towards these objectives in the last few years, fundamental understanding of the factors resulting in performance loss and materials degradation is still lacking. Several key elements in overcoming these challenges, such as in situ diagnostic tools, modelling and simulation and accelerated stress tests are discussed. A general framework for the improvement of performance degradation and durability is presented in order to achieve the US DOE cost target of USD for the fuel cell stack, while advancing operational imperatives such as freeze start, higher temperature operation and reduced reliance on external humidification. [Copyright &y& Elsevier]

Abstract: Although FRP composites are increasingly being used for the rehabilitation of civil infrastructure, there is still a lack of well documented long-term durability data, and of design methodologies that explicitly consider effects of deterioration over time at a structural level. This paper provides results of an investigation aimed at assessing the effect of deterioration over time, at the materials level, on the effectiveness of FRP jackets used for seismic retrofit. Three different systems are investigated and results of accelerated testing are used to provide predictive equations for long-term performance of the material, which are then used to analyze effectiveness at the level of seismic retrofit through four specific cases. The effect of deterioration is expressed, for ease in comparison, to an increase in the required thickness of the jacket with expected service-life. Results using unexposed values for materials performance are compared to those obtained using the values recommended by ACI-440 procedures, as well as through the use of time-dependent materials degradation models. It is shown that the ACI recommendations for durability may be excessively conservative for the 50-year period considered herein. The use of the proposed predictive methodology for materials durability combined with the analytical tools for design of FRP jacket thickness are shown to not only enable a better assessment of required jacket thickness but can also enable assessment of the dominant mechanism controlling selection of thickness which can change with time of exposure. Results of the accelerated tests are also linked to field exposure results providing a set of correlation factors. [Copyright &y& Elsevier]

The potential benefits from using a novel vinyl-terminated long alkyl-chain self-assembling silane (VTS) have been investigated. A relatively high water contact angle of 83° was found for water on the VTS-pretreated soda-lime glass surface. This revealed that the degree of hydrophobicity of this surface was far more pronounced than for the ultrasonically-cleaned glass surface or the γ-glycidoxypropyltrimethoxy silane (GPS)–pretreated glass surface, which gave contact angles of 14° and 42°, respectively. Further, good agreement between the measured and the theoretical contact angles for a fully adsorbed vinyl-terminated self-assembled monolayer surface implied that the VTS molecules were adsorbed with the vinyl-terminal groups orientated away from the glass surface. Indeed, X-ray photoelectron spectroscopy (XPS) analysis confirmed that the VTS molecules were adsorbed as a monolayer with the vinyl-terminal groups orientated away from the glass surface. Double-cantilever beam joints were prepared using these various pretreated-glass substrates, using an epoxy adhesive, and they were tested employing a fracture-mechanics approach. The adhesive fracture energy, GC, of the VTS-pretreated glass/epoxy joints was found to be far lower in value than for the ultrasonically cleaned joints or the GPS-pretreated joints. The potential applications of this novel long alkyl-chain silane are twofold: (a) the relatively very poor adhesion of the VTS pretreatment enables this silane to be used as an excellent abhesive layer, i.e., as a release agent, and (b) the presence of reactive vinyl-terminal groups might allow this silane to be activated to form functional groups that may then react with an adhesive, such as an epoxy resin, and so act as an excellent adhesion promoter to increase the durability of the adhesive joint. [ABSTRACT FROM AUTHOR]

Gloss retention of waterborne acrylic architectural paints is one of many properties defining exterior durability. Assessing gloss retention is a time consuming process, and accelerated weathering protocols (Weather-Ometer®) typically have poor correlation with natural exposures for this class of paints. The recent development of new analytical techniques for assessing automotive paint durability raises the possibility of detecting subtle changes in short-term natural exposures that would be predictive of long-term gloss retention; however, extension to architectural paints has yet to be demonstrated. To test the concept, seven paints based on different aqueous emulsion polymers were exposed to natural weathering at the same time for 12 weeks at the Paint Quality Institute (PQI) test site, and were then examined using scanning probe microscopy, optical profilometry, chemiluminescence, XPS, and FTIR. These paints were also exposed for 1000 hr in a Weather-Ometer (WOM). Scanning probe microscopy, optical profilometry, chemiluminescence, FTIR, and the WOM results all showed poor correlation with 96-week natural exposure at the PQI test site. The lack of correlation for the WOM results emphasizes the crucial importance of using natural weathering to assess gloss retention. In contrast, the XPS shows some promise for qualitatively predicting subsequent gloss loss and appears worthy of further exploration. As employed here, the XPS was used to monitor the ratio of pigment (Al, Si, and Ti) to carbon coming from the TiO2 in the top few nanometers of the paint surface. A correlation (R² = 0.731) was found between gloss retention after 96 weeks and the change (2 versus 12 weeks of exposure) in pigment to carbon ratio. This correlation is probably sufficient to rank a series of paints and allow for an assessment against well-established controls. While promising, XPS has some issues. Surface contamination, equipment expense, the considerable expertise required, and precision make utility for screening less than ideal. [ABSTRACT FROM AUTHOR]

Accelerating the photodegradation of commercial polymeric materials has great practical importance in the weathering community. However, questions exist as to whether high radiant flux exposure results can be extrapolated to in-service exposure levels. Based on the reciprocity law, the photoresponse of a material is dependent only on the total energy to which the specimen is exposed, and is independent of the exposure time and the intensity of the radiation taken separately. An experiment to validate the applicability of the reciprocity law for polymeric coatings has been carried out using the NIST integrating sphere-based ultraviolet (UV) weathering device. A nonpigmented, non-UV stabilized acrylic-melamine coating was exposed to six different UV radiation intensities ranging from 36 W/m² to 322 W/m² and in the spectral region between 290 nm and 400 nm. Chemical changes in the coating due to UV exposure were measured with transmission Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. Using two dose-damage models, the reciprocity law photoresponse for this polymeric system was verified for different photodegradation mechanisms, including chain scission, oxidation, and mass loss. [ABSTRACT FROM AUTHOR]

To achieve successful commercialisation of new advanced windows and solar façade components for buildings, the durability of these need to be demonstrated prior to installation by use of reliable and well-accepted test methods. In Task 27 Performance of Solar Facade Components of the IEA Solar Heating and Cooling Programme work has therefore been undertaken with the objective to develop a general methodology for durability test procedures and service lifetime prediction methods adaptable to the wide variety of advanced optical materials and components used in energy efficient solar thermal and buildings applications. As the result of this work a general methodology has been developed. The proposed methodology includes three steps: (a) initial risk analysis of potential failure modes, (b) screening testing/analysis for service life prediction and microclimate characterisation, and (c) service life prediction involving mathematical modelling and life testing.The applicability of the working scheme to be employed in the development of durability test procedures has been analysed for selective solar absorber surfaces and polymeric glazing materials in flat plate solar collectors. The examples show the great applicability of the general methodology for accelerated life testing. This will allow much shorter development cycle times for new products and will allow improvements to be identified and readily incorporated in new products prior to market introduction. [Copyright &y& Elsevier]

Products must come to market quickly, be more reliable and cost less. The problem is that statistical measures take time. There is a clear need for actionable information about the robustness or durability of a product early in the development process. In a Failure Mode Verification Test (FMVT), the analysis is not statistical but is designed to check two assumptions. First, that the design is capable of producing a viable product for the environments applied. Second, that a good design and fabrication of the product would last for a long period of time under all of the stresses that it is expected to see and would accumulate stress damage throughout the product in a uniform way. Testing a product in this way leads to three measures of the product's durability: (1) design maturity, the ratio between time to first failure and the average time between failures after the first failure; (2) technological limit, the time under test at which fixing additional failures would not provide a significant improvement in the life of the product; and (3) failure mode histogram, which indicates the repeatability of failures in a product. Using techniques like FMVT can provide a means of breaking the tyranny of statistics over durability and reliability testing in a competitive business climate. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The adhesive fracture energy, G c , of aluminium alloy and steel joints bonded with a rubber-toughened epoxy adhesive has been measured using monotonically loaded tests. Such tests have been conducted at different levels of relative humidity, and two surface pretreatments have been employed for the substrates prior to bonding: a simple grit-blast and degrease (GBD) pretreatment or a silane primer (GBS) pretreatment. When G c was plotted against the crack velocity, three regions of fracture behaviour could be distinguished. At low rates of displacement the crack grew in a stable manner, visually along the interface, and relatively low crack velocities could be readily measured. This was termed "Region I," and here the value of the adhesive fracture energy was relatively low and decreased steadily as the relative humidity was increased. On the other hand, at relatively high rates of displacement the crack grew in a stick-slip manner mainly cohesively in the adhesive layer at approximately 20 km/min. This was termed "Region III," and here the value of G c was relatively high and independent of the relative humidity. In this region the crack was considered to grow faster than the water molecules were able to reach the crack tip, which explains the independence of G c upon the test environment. In between Region I and Region III, a transition region was observed, which was designated "Region II." The major effect of the GBS pretreatment, compared with GBD pretreatment, was to increase the value of G c both in Regions I and III, although the presence of the silane primer had the greater effect in Region I. [ABSTRACT FROM AUTHOR]

Novel interconnect technologies leveraging low melting temperature solders, such as multiwire interconnects, are being deployed in photovoltaic (PV) modules for improved reliability through interconnect redundancy and lower thermal loads during interconnection and lamination. However, the equivalency of standardized accelerated testing to field conditions has not yet been established for these emerging technologies. In this study, the thermomechanical fatigue resistance of low temperature solder alloys is investigated and compared to that of conventional SnPb to assess the acceleration behavior of these alloys. While InSn is shown to have sufficient thermomechanical fatigue resistance on the order of that of SnPb, these results indicate Sn–Bi alloys may have poor thermomechanical fatigue resistance at field conditions. The results also show that Sn–Bi alloys have thermal cycling acceleration factors of less than one. This indicates that the standardized accelerated thermal cycling test, such as that in IEC 61215, will produce misleading results for Sn–Bi alloys and that unique testing is required for this PV module architecture. Though accelerated thermal cycling may be a meaningful qualification test for SnPb solder joints, these results suggest that mechanical loading may be a more appropriate test for Sn–Bi multiwire interconnects. This is due to the distinct processing and geometry of multiwire interconnects which may allow for mechanical, rather than strictly metallurgical interconnections. • Eutectic InSn damage accelerates similar to conventional SnPb under thermal cycling. • Conversely, Sn–Bi alloy damage is not accelerated with thermal cycling. • Sn–Bi alloys expected to have poor thermomechanical fatigue resistance in the field. • Conventional accelerated testing may then yield misleading results for Sn–Bi alloys. • Multiwire designs may allow for interconnection not susceptible to thermal fatigue. [ABSTRACT FROM AUTHOR]

• Longer wetting times accelerate PSA damage in partially immersed specimens. • PSA damage principally occurs during the formation of mirabilite. • Lowering the w/c proved to be very effective against PSA. • 5% sodium sulfate solution is not high enough for accelerated PSA tests. • Full immersion tests give higher mass loss but may cause combined sulfate attack. There is currently no standard test method to determine the physical salt attack (PSA) resistance of cement-based materials. In this study, several accelerated test methods for PSA were evaluated. This was accomplished by testing concrete mixtures in partial and full immersion in sodium sulfate solutions at different concentrations, temperature, and relative humidity cycling. A total of nine concrete mixtures made from three types of portland cement at three different water-to-cement ratios (w/c) were used in this research to compare each method with materials of different qualities. The results showed that a 5% sodium sulfate solution was too dilute to be used in accelerated PSA testing, whereas increasing the concentration to 10% showed better results. In addition, it was found that damage occurred during low temperatures at high relative humidity compared to high temperatures at low relative humidity. Testing fully immersed specimens in 30% sodium sulfate solution gave the highest mass loss, but the damage was located at the bottom third of the specimens because of a concentration gradient that formed in the solution. [ABSTRACT FROM AUTHOR]