Lifetime Expectancy Research Articles

Power Module Interconnection Reliability in BTS Applications

In this paper, the reliability of RF power transistors’ solder attachments is characterized through experiments and simulations. Test cases consisted of power amplifier (PA) modules on AlSi10Mg substrates with either a low or high mutual thermal mismatch. The module’s flange interconnections were stressed by means of thermal cycling testing (TCT) in the 15 °C–95 °C range. Scanning acoustic microscopy (SAM) was used intermittently to inspect the interconnections of selected structures during cycling breaks. Optical cross-polarization microscopy and scanning electron microscopy were used in the failure analysis of the solder joints. Different materials and dimensional variations were tested in simulations to observe differences in thermal stress. The viscoplastic behavior of lead-free solder in the interconnection was modeled using Anand’s constitutive equations. The first cracks could be observed with SAM after 100 cycles. SAM imaging showed that in the worst case, 72% of the interconnection area had cracked at the end of the 1100-cycle TCT. Only a marginal amount of cracks could be observed in PA modules with a better coefficients of thermal expansion match to the substrate. Simulations indicated that it is possible to decrease creep energies significantly and thereby increase the lifetime expectancy of interconnections by selecting the correct materials and structures.

Atmospheric Stress Corrosion Cracking of Stainless Steel Rock Climbing Anchors, Part 2: Laboratory Experiments

Atmospherically-induced stress corrosion cracking (AISCC) in the presence of chloride deposits has been responsible for considerable incidents of rock climbing anchors breaking under minimal loads in seaside locations, putting climbers lives at stake. However, to date, failures due to AISCC have only been documented in anchors made of Type 304/304L and similar, and no rigorously documented failures have been shown to occur to Type 316/316L anchors. In order to support preparation of a new standard classifying anchors according to their corrosion resistance, the influence of environmental parameters such as periodic washing of chloride deposits, electrolyte pH, and type of rock on AISCC initiation and crack growth rate was studied in laboratory conditions by exposing U-bent specimens of stainless steel Types 321, 304, and 316L with MgCl2 deposits in air at 40°C to 50°C and at 35% to 45% relative humidity. The type of rock and electrolyte pH were not critical parameters for AISCC. Alkaline conditions only slightly prolonged stable crack initiation period and decreased the crack growth rate. Periodic washing in sufficiently short intervals was capable of significantly retarding or even arresting AISCC. The crack growth rate in Type 316L stainless steel was 2- to 3-fold slower than in the molybdenum-free Types 304 and 321. These last two effects are quite likely responsible for the lack of failures observed in Type 316/316L. In view of the lifetime expectancy of rock climbing anchors and other safety-relevant members, the crack growth rate was unacceptably high in all studied materials and their installation should be avoided in vulnerable seaside regions.

Effect of strain ratio on cyclic deformation behaviour of 7050-T6 aluminium alloy

This paper aims at investigating the strain ratio effect on cyclic deformation behaviour of 7050-T6 aluminium alloy. Low-cycle fatigue tests are conducted under strain-controlled conditions at three strain ratios (−1, 0, and 0.5) with strain amplitudes in the range 0.60–1.75%. Microstructure is analysed by optical microscopy, transmission electron microscopy and X-ray diffraction, and fracture surfaces are examined by scanning electron microscopy and transmission electron microscopy. The results show that the material exhibits a cyclic strain-softening behaviour whose degree increases with increasing values of strain ratio and decreasing values of strain amplitude. Under non-zero mean strain, full relaxation of mean stress is only observed at higher strain amplitudes. A second order logarithmic model is proposed to account for the mean stress relaxation rates. Lifetime expectancy is reduced as the strain ratio raises which is consistent with the progressive increment of fatigue striation spacing observed in the fractographic analyses.

Comparison of potential long-term costs for preventive dentistry treatment of post-orthodontic labial versus lingual enamel cavitations and esthetically relevant white-spot lesions: a simulation study with different scenarios

BackgroundPost-orthodontic white-spot lesions (WSL) in esthetically relevant incisor and canine areas impair dentofacial esthetics, and preventive dentistry treatment is definitely required in case of enamel cavitations. The incidence of lingual post-orthodontic WSL and cavitation following lingual MB treatment has been reported to be distinctively decreased compared to labial MB treatment. Moreover, lingual WSL do not impair dentofacial esthetics. It was the objective of this study to calculate consequential costs of preventive dental care necessary to recover labial or lingual post-orthodontic cavitations as well as esthetically relevant WSL following either labial or lingual MB interventions.MethodsMB treatments (labial / lingual) were simulated in 1,000,000 patients between the ages of 12-18Y, with a median residual life time expectancy of 58Y based on local mortality tables. Range of MB Tx duration was 9–45 mo. Frequencies of post-orthodontic (labial / lingual) enamel damages were derived from large-scale WSL incidence studies. Anterior composite survival rates were based on a systematic review on the subject. Within the context of the German dental fee system (GOZ 2.3 and 3.5 fee increments), simulation of costs for enamel damage treatment and re-treatment (maximum: 5x) were based on single-surface composite restorations for lingual or labial cavitations and labial WSL treatment; and lingual WSL fluoridation.ResultsOverall mean total costs for Tx and re-Tx of both WSLs and cavitations may sum up to 1718.91 Eur in the high-cost (GOZ 3.5) scenario for conventional MB cases, versus 19.94 Eur for lingually treated cases, given that renewal of simulated single-surface restorations takes place at 15-year intervals. When focussing on patients diagnosed with least of one WSL, and/or cavitation, these mean costs increase up to 2332.35 Eur for conventionally treated MB patients, or 65.03 Eur for lingual MB patients.ConclusionCosts for repeated treatment of post-orthodontic enamel damages produced by conventional vestibular fixed appliances may easily exceed the initially higher costs associated with lingual orthodontic treatment. Judged economically in the long term, lingual MB Tx may be considered as a more cost-effective solution for a correction of malocclusion.

Assessment of mechanical properties of Silicon Carbide and Graphene reinforced aluminium composite

Abstract Metal Matrix Composite is widely replacing the older materials in the area of aerospace applications. The evolving requirement of superior properties and increased lifetime expectancy has led to formation of newer composite materials. An attempt has been made to formulate and evaluation of the fundamental properties of the developed composite. AA 7075 aluminium material is reinforced with fixed percentage of Silicon Carbide and Graphene in different proportions. Three samples were made and mechanical properties and Microstructural properties were studied. The graphene was increased by order of 3% of net weight of composite varying from 0% to 6%.

Influence of cross passages temperatures on the life-cycle cost of technical equipment in a railway tunnel

In order to achieve the climate goals, the implementation of sustainable construction is becoming more and more topical in the construction sector. Due to very long service lifes especially in railway projects, the consideration of life-cycle aspects into the early design process is of great importance. Regarding the assessment of the economic pillar of sustainability, life-cycle costing has become an established method. This study presents the application of life-cycle cost analysis (LCCA) for decision aiding in railway construction. The two tunnel tubes of the project Koralmtunnel (KAT) are connected with approximately 70 cross-passages (CPs) at intervals of around 500 m. These CPs serve as escape-ways and additionally host utility rooms for technical equipment (telecomunication, power supply and remote control). First thermal simulations revealed indoor temperatures up to 80[openbullet]C due to the heat release of the technical equipment without implementation of technical cooling systems in operation phase. This is caused by the limited heat transfer with the surrounding rock and with the adjacent running tubes. Therefore, the implementation of a cooling system is necessary. It is stated that higher indoor temperatures lead to reduced service lifes of the installed telecommunication systems. By the application of Arrhenius equation, the influence of several indoor target temperatures on the expected life time of the installed telecommunication systems has been determined. In order to meet target temperature requirements appropriate scenarios including different cooling scenarios have been designed. Finally, LCCA by application of the net-present value-method (NPV-method) was conducted in order to determine the most economical solution regarding CPs cooling systems based on selected target-temperatures.

Including power management strategies and load profiles in the mathematical optimization of energy storage sizing for fuel consumption reduction in maritime vessels

Abstract Choosing the optimal type and size of energy storage for a given hybrid maritime vessels is challenging. Investment cost, fuel saving and energy storage expected life time will be affected by the choices. Furthermore, the optimum choices depend on the operation profile of the vessel as well as safety related constraints in different vessel mode of operations. In addition, the optimum power management strategy will be mode dependent as well as dependent on the type and size of onboard energy storage. Finally, the total system has to fulfill certain safety related rules and regulations that typically both favour the use of storage and set some constraints to the size and the utilization of the storage. In this paper we propose a mathematical optimisation model called OBLIVION that stands for “Optimised Battery Lifetime In Vessels Internal Operations and Networks”. OBLIVION is created to support battery investment decisions. Beyond including battery degradation and desired battery lifetime in the choice, the model facilitates analysis of how the investment decisions change for different combinations of vessel operation modes. The key contribution of this paper is the proposed methodology to formulate technical and safety constraints, represent different vessel modes of operation and battery storage degradation in a way suitable for inclusion within mathematical optimisation models. Moreover, analyses that demonstrate how these features affect the storage investment decisions are presented. Mathematical formulations of constraints such as closed and open bus-tie breaker operation, true spinning reserve requirements as well as spinning reserve provided by batteries are included as well.

Development and Evaluation of a Design Thinking Process Adapted to Frugal Production Systems for Emerging Markets

Frugal describes a new strategic approach which is often praised to be the key to emerging markets. More than four billion people will live in these extremely price-conscious markets in the near future. Therefore, processes for frugal products become more and more important in engineering departments of high-tech manufacturers who want to expand to emerging markets as they are struggling with local saturated markets. However, in order to meet the needs of price-sensitive customers a frugal product should be focused on core functionalities, a significant price reduction and also on an optimized performance level taking into account the expected life time and local conditions. In order to do this successfully, a new mindset for these emerging markets and, along with this, the necessity to loosen up their traditional development processes towards a more agile approach with for example the Design Thinking (DT) process is often claimed in literature. As these literature contributions are mainly based on descriptive fundaments, this paper presents an adapted process which links the basic ideas of Design Thinking and Frugal Innovation with the focus on production systems for emerging markets. The application of the process is shown by a use case.

Fatigue behaviour of maraging steel samples produced by SLM under constant and variable amplitude loading

This paper addresses the fatigue behaviour of AISI 18Ni300 samples manufactured by selective laser melting under both constant- and variable-amplitude loading. The fatigue campaign encompasses a series of low-cycle strain-controlled fatigue tests performed under fully-reversed conditions at various strain amplitudes, and a series of high-cycle stress-controlled fatigue tests performed under pulsating conditions at various stress ranges considering both constant- and variable-amplitude loading spectra. Fatigue life predictions are performed on the basis of the SWT parameter along with the Miner’s law. This approach has demonstrated to be sufficiently reliable to predict the lifetime expectancy in maraging steel samples produced by selective laser melting.

Strategic View on Cobot Deployment in Assembly 4.0 Systems

Collaborative robots (cobots) are intended to physically interact with humans in a shared workspace. While cobots research proliferated in the recent decade, only scant attention was given to the strategic consideration of deploying them. The obvious strategic consideration is related to economic cost-benefits trade-off. However, the economic decision is tightly tied to the technology improvement rate, as cobots lifetime expectancy strongly depend on the technological developments. In this regard, the difference between different types of cobots may be dramatic. Another strategic issue is the sociological effects including the reaction of the operators and unions to cobot deployment. This paper reviews the related literature and proposes a model to analyze the underlying factors and facilitate the decision making process of: where and when to deploy which cobots.

Microstructural Evolution and Sintering of Suspension Plasma-Sprayed Columnar Thermal Barrier Coatings

Suspension plasma spray (SPS) is capable of producing coatings with porous columnar structure, and it is also a much cheaper process compared to the conventionally used electron beam physical vapor deposition (EB-PVD). Although TBCs with a columnar microstructure that are fabricated using SPS have typically lower thermal conductivity than EB-PVD, they are used sparingly in the aerospace industry due to their lower fracture toughness and limited lifetime expectancy. Lifetime of TBCs is highly influenced by the topcoat microstructure. The objective of this work was to study the TBCs produced using axial SPS with different process parameters. Influence of the microstructure on lifetime of the coatings was of particular interest, and it was determined by thermal cyclic fatigue testing. The effect of sintering on microstructure of the coatings exposed to high temperatures was also investigated. Porosity measurements were taken using image analysis technique, and thermal conductivity of the coatings was determined by laser flash analysis. The results show that axial SPS is a promising method of producing TBCs having various microstructures with good lifetime. Changes in microstructure of topcoat due to sintering were seen evidently in porous coatings, whereas dense topcoats showed good resistance against sintering.

Extending Battery Lifetime by Avoiding High SOC

The impact of ageing when using various State of Charge (SOC) levels for an electrified vehicle is investigated in this article. An extensive test series is conducted on Li-ion cells, based on graphite and NMC/LMO electrode materials. Lifetime cycling tests are conducted during a period of three years in various 10% SOC intervals, during which the degradation as function of number of cycles is established. An empirical battery model is designed from the degradation trajectories of the test result. An electric vehicle model is used to derive the load profiles for the ageing model. The result showed that, when only considering ageing from different types of driving in small Depth of Discharges (DODs), using a reduced charge level of 50% SOC increased the lifetime expectancy of the vehicle battery by 44–130%. When accounting for the calendar ageing as well, this proved to be a large part of the total ageing. By keeping the battery at 15% SOC during parking and limiting the time at high SOC, the contribution from the calendar ageing could be substantially reduced.

Polycyclic Aromatic Hydrocarbons in Different Varieties of Rice (Oryza sativa) from Yobe State, Nigeria

The present study determined the levels of sixteen polycyclic aromatic hydrocarbons (PAHs) in rice (Oryza Sativa) samples from six agricultural locations in Bade and Karasuwa Local Government Areas, Yobe State, Nigeria. Four varieties of rice (FARO 42, 44, 45 and 52) were collected for this study. The concentrations of PAHs in the study rice samples were lower than the maximum allowable concentration (MAC), average daily dose (ADD) of PAHs in the different variety of rice from the six agricultural locations shows that FARO 44 had the highest ADD (5.84 x1011 mg/kg), while FARO 52 shows the lowest ADD (1.20 x1015 mg/kg). The potential for non-carcinogenic PAHs in this study revealed that FARO 42 has the highest hazard index (2.04 x1011 mg/kg). Result from incremental lifetime expectancy cancer risk shows that FARO 44 from Jawa had the highest value (4.19 x1010 mg/kg), while the lowest value (7.61 x1015 mg/kg) was recorded for FARO 52 from Rina Kuna agricultural location. Results from the present study shows that the rice samples from the study locations are safe for human consumption and not significantly contaminated by PAHs.

Lifetime Comparison of Power Semiconductors in Three-Level Converters for 10-MW Wind Turbine Systems

The power electronic converter, especially the power semiconductor, is a major contributor to the failure rates of the wind turbine drivetrain. As the temperature is a major driving factor behind the failure mechanisms of these power semiconductors, the choice of topology and switching strategy can have a significant effect on the reliability of the converter. This paper presents a detailed comparison of several three-level converter topologies and switching strategies on the basis of loss distribution, thermal, and lifetime performance. This investigation is done through simulations on a 10-MW direct drive permanent magnet drivetrain. The study shows that overrating in the form of using overrated topologies, or the use of overrated components can result in large gains in lifetime expectancy and quantifies these gains. It concludes that the improvements offered by overrated topologies and overrated components are comparable and this use of the overrated topologies do not offer a significant advantage over the use of topologies with overrated components.

Reliability Testing and Stress Measurement of QFN Packages Encapsulated by an Open-Ended Microwave Curing System

In this paper, the influence of microwave curing on the reliability of a representative electronic package is examined by reliability testing and measurement of residual stresses. A LM358 voltage regulator die was mounted to an open quad flat no-leads (QFN) package for reliability testing. For the stress measurement, a specifically designed stress measurement die was mounted to the QFN package. The chips were encapsulated with Hysol EO1080 thermosetting polymer material. Curing was performed using an open-ended microwave oven system equipped with in situ temperature control. Three different temperature profiles for microwave curing were selected according to the requested degree of cure and chemical composition of the cured material. A convection cure profile was selected for the control group samples. Temperature cycle tests and highly accelerated stress tests (HAST) were performed on a total number of 80 chips. Ninety-five QFN packages with stress measurement chips were also manufactured. The increased lifetime expectancy of the microwave-cured packaged chips was experimentally demonstrated and measured between the 62% and 149% increased lifetime expectancies after temperature cycle test (TCT), and between 63% and 331% after a HAST and TCT compared to conventionally cured packages. The analysis of specifically designed stress test chips showed significantly lower residual stresses ranging from 26 to 58.3 MPa within the microwave-cured packages compared to conventionally cured packaged chips, which displayed residual stresses ranging from 54 to 80.5 MPa. Therefore, this paper provides additional confidence in the industrial relevance of the microwave curing system and its advantages compared to the traditional convection oven systems.

The Influence of State-of-Charge on Ageing in Commercial Li-Ion Pouch Cells

Vehicle manufacturers are increasingly electrifying their vehicles using Lithium-ion batteries (LiBs) as the energy storage unit. With a very high battery cost, the requirements on LiB life and performance are necessarily stringent and much effort goes into understanding how these properties are influenced by the conditions of use. For electric vehicles a large State-of-Charge (SOC) operation window has to be balanced with the lifetime expectancy. Being able to correlate load cycles to a specific type of ageing is crucial to understand how to better utilize the LiBs - improving the accuracy of lifetime predictions and optimizing the performance/lifetime balance in the vehicle. A physics-based ageing model of a commercial Li-ion pouch cell with a graphite anode and a blended LMO/NMC cathode has been developed. The model is based on the Newman theory [1], as implemented in COMSOL [2-6], and is a direct continuation of the work in [6]. The growth of a solid electrolyte interphase (SEI), resulting in increased resistance and capacity loss, constitutes the main ageing mechanisms of the model, which has been tuned with experimental test data as input. The SEI growth has also been linked to a change in active material porosity and thereby a reduced electrolyte volume in the electrode. The resulting effect on the cell resistance and capacity during various test conditions is determined, and the impact from the different ageing parameters evaluated. The experimental tests used synthetic load cycles for various C-rates, at different Depth of Discharge (DOD) and at different SOC. The results show an expected increased ageing with C-rate, but more surprising is the ageing patterns seen for small DOD, at various SOC intervals, which do not follow the trend observed for LiBs with LFP cathodes [7]. The LiB here degrade most strongly at high SOC (> 60%), in accordance with previous research, while at SOC < 30% ageing is impressively slow. The slow capacity degradation of the cells in SOC intervals < 30% make their cycle lifetime more than 3x longer compared to the cells run at high SOC. The developed ageing model can successfully capture the difference in capacity loss due to larger SEI growth at high SOC.

Long-Term Effect of Cholinesterase Inhibitors and Special Nursing Home Replacement on Lifetime Expectancy for Alzheimer Disease and Dementia with Lewy Bodies: The Osaki-Tajiri Project

Long-Term Effect of Cholinesterase Inhibitors and Special Nursing Home Replacement on Lifetime Expectancy for Alzheimer Disease and Dementia with Lewy Bodies: The Osaki-Tajiri Project

Gearbox condition monitoring in wind turbines: A review

Abstract Wind turbine technology is experiencing rapid growth with respect to size, market share, and technological design. Operational and maintenance cost directly determine whether the system is efficient in terms of energy production in comparison with other types of power plants. Condition monitoring of wind turbines is the major field of studies in recent years aiming to increase lifetime expectancy of components while reducing operation and maintenance cost. Operators and researchers are focusing on improving fault detection techniques in order to render wind turbines more reliable. Gearbox in wind turbines has the greatest share of downtime among all other components affecting directly the cost of operation and maintenance. This paper gathers a review on different methods and techniques for gearbox condition monitoring in wind turbines. Furthermore, various methods and techniques in the literature will be presented in order to get an insight onto the most used methods in wind turbine gearbox condition monitoring. Challenges and future aims are also discussed to determine the focus of condition monitoring systems.

On the Impacts of PV Array Sizing on the Inverter Reliability and Lifetime

To enable a more wide scale utilization of photovoltaic (PV) systems, the cost of PV energy should be comparable to or even lower than other energy sources. Due to the relatively low cost of PV modules, oversizing PV arrays becomes a common approach to reduce the cost of PV energy in practice. By doing so, the total energy yield can be increased under weak solar irradiance conditions. However, oversizing the PV array will increase the loading of PV inverters, which may have undesired influence on the PV inverter reliability and lifetime. In that case, it may result in a negative impact on the overall PV energy cost, due to the increased maintenance for the PV inverters. With the above concern, this paper evaluates the reliability and lifetime of PV inverters considering the PV array sizing. The evaluation is based on the mission profile of the installation sites in Denmark and Arizona, where the reliability-critical components such as power devices and capacitors are considered. The results reveal that the variation in the PV array sizing can considerably deviate the reliability performance and lifetime expectation of PV inverters, especially for those installed in Denmark, where the average solar irradiance level is relatively low. In that case, a certain design margin in term of reliability is required to ensure high-reliable operation of PV inverters.

Evaluation of the volatile organic compound emissions in modern and naturally aged Japanese paper

Abstract Volatile organic compounds (VOCs) can have a strong effect on cellulose degradation, contributing in decreasing the lifetime expectancy of the paper materials, widely employed in the field of conservation. In this work, we investigated several industrial and homemade Japanese papers, as well as fibers, evaluating VOCs emission by using solid-phase micro extraction coupled with gas chromatography–mass spectrometry (SPME-GC/MS). Acetic acid and 1-butanol were highly detected in industrial and homemade papers rather than fibers, suggesting that the emission of these compounds is influenced by the production process more than by the raw material itself. Conversely, N-N dimethyl formammide was peculiar of industrial processes. Ketones, aldehydes and heavier alcohols were preferentially emitted by fibers and homemade papers. The higher emission of furfural from fibers rather than on papers place new questions about the use of this compound to evaluate the degradation state of the paper material that should be carefully evaluated.