Accelerated Life Cycle Testing Research Articles

Life cycle testing and reliability analysis of prismatic lithium-iron-phosphate cells

ABSTRACT A cell’s ability to store energy, and produce power is limited by its capacity fading with age. This paper presents the findings on the performance characteristics of prismatic Lithium-iron phosphate (LiFePO4) cells under different ambient temperature conditions, discharge rates, and depth of discharge. The accelerated life cycle testing results depicted a linear degradation pattern of up to 300 cycles. Linear extrapolation reveals that at 25°C temperature, an increase in the discharge rate from 0.5 C to 0.8 C reduces the cycle life significantly by 52.9%. On the other hand, at a constant discharge rate, an increase in temperature reduced predicted cycle life in the range of 23.2–41.36%. Lithium-ion cells’ reliability modeling and analysis was carried out using an exponential distribution showing the increasing failure rate with age, with the temperature significantly reducing the expected life of the cells.

Application of particle filter variants to estimate the remaining useful life

Dynamic loadings encountered by clutch motor of an Automated manual transmission (AMT) passenger vehicle require apposite assessment of nonlinear characteristic of the degrading system to accurately predict the remaining useful life (RUL) for implementation of condition based maintenance (CBM) schedule. The present study involves the application of three variants of particle filter (PF) with various resampling techniques to account for heavy tailed observations and non-Gaussian characteristic of noise to improve the accuracy of RUL estimation. Degradation dataset was generated using accelerated life cycle test (ALCT) on hardware-in-loop (HIL) laboratory of a large Indian automotive company. A comparative analysis of the results showed 91.5, 93.2, and 94.9% enhancement in the efficacy of RUL estimation due to canonical, unscented, and improved unscented particle filters (i-UPF) vis-a-vis the ordinarily fitted exponential degradation model.

How to Capture Movement

How to Capture Movement

Electroluminescence image analysis of a photovoltaic module under accelerated lifecycle testing.

Electroluminescence (EL) imaging of Si-based photovoltaic (PV) modules is used widely to spatially detect and characterize electrical defects, including handling and degradation-induced cracking of the component Si cells that are associated with reductions in module performance. In the present study, a commercial polycrystalline silicon PV module was subjected to accelerated lifecycle test environmental conditions and examined as a function of environmental exposure time using EL imaging. The approach followed pixel intensity distributions over each individual PV cell and confirmed a positive correlation between module conversion efficiency and results of the image analysis. Overall, an average of a 2.5% reduction in normalized EL intensity was correlated to a 0.35% reduction in actual power conversion efficiency (or a 2.3% decrease in relative efficiency). The imaging analysis technique offers a rapid, unsupervised means to assess EL data in lieu of conventional visual interpretation.

Laboratory accelerated and field exposure testing of MgRP and MgORP on AA2024-T351: Chemical and electrochemical protection effects

Two Mg-based coatings consisting of Mg-rich primer (MgRP) and MgO-rich primer (MgORP) with and without topcoat were exposed to laboratory accelerated lifecycle testing (LALT) and outdoor field environments. The coatings were tested in parallel exposure studies utilizing ASTM B117, modified ASTM B117 (cyclic wet-dry, dark-UV exposure in ASTM synthetic ocean water), rural inland (Charlottesville, VA), and coastal marine (Kennedy Space Center) field exposure. Several characterization and electrochemical diagnostic techniques were used to continuously assess coating performance as a function of time in various exposures, enabling comparison of LALT to field exposures. The coating systems were evaluated with respect to the intact coating and to a machined scribe defect. The fate of Mg2+ upon dissolution of Mg and MgO with respect to pigment depletion, corrosion product formation, and repartitioning from the coating into the scribe was monitored with XRD and EDS. The capacity for MgRP and MgORP to provide barrier, cathodic, and chemical corrosion protection to AA2024-T351 substrate was evaluated. The ultimate ability of these coatings to protect the AA2024-T351 substrate both in the scribe and under the coating was gauged with optical profilometry assessment of corrosion damage. The Mg and MgO-based coating systems exhibited several desirable aspects of a corrosion preventative coating. The corrosion damage quantified both under the intact coating and within the scribe was much less than the corrosion damage measured on uncoated controls. Within a given exposure, the reduction of corrosion damage in the scribe correlated with the amount of Mg2+ which was released from the coating and repartitioned into the scribe. The open circuit potential of the coated substrate was depressed to more negative potentials than the bare substrate in 5 wt% NaCl, with non-topcoated samples establishing more negative potentials. The barrier properties remained high throughout the exposures for topcoated samples, which also better preserved the pigment from depletion. Comments are made regarding differences between the Mg and MgO-based coatings and the various laboratory and field exposures.

Galvanic Corrosion of Automotive Mixed Metal Substrates: Fundamental Understanding

Dissimilar metal joining is of increasing interest in many structural applications due to its potential to enable light weighting. Light-weight substrates such as aluminum alloys, magnesium alloys and carbon-fiber reinforced polymer (CFRP) are increasingly used in place of conventional steels due to their high strength-to-weight ratios. Two of the main challenges associated with the increased usage of mixed metal systems are galvanic corrosion and challenges with classical joining methods. 1,2. Most joining methods such as riveting, mechanical fasteners, and welding, results in electrical connection between the joined metals, which poses galvanic corrosion issues. Even galvanic isolation approaches such as the use of adhesives can cause galvanic corrosion problems due to the complexity of mixed metal assemblies. In galvanic coupling scenarios, the less noble material experiences severe corrosion and more noble material is protected. It is important to build a fundamental understanding of this phenomenon relative to the metallurgy and electrochemistry of the substrates, as well as the coupling method, to provide effective corrosion mitigation solutions. Electrochemical test techniques such as zero resistance ammeter measurements, open circuit potential measurements, and potentiodynamic polarization were utilized to understand effect of substrate type and solution pH on galvanic corrosion. In addition to the substrate effect, the effect of fastener type on galvanic corrosion between substrate and fasteners was also investigated for selected systems. The influence of joining methods such as self-piercing rivets, adhesives, and mechanical fasteners on galvanic corrosion was also studied. Galvanic and self-coupled coupons were exposed to standard laboratory accelerated life cycle test methods. Wedging by corrosion products, scribe creep, and corrosion volume loss were each characterized to quantify the extent of galvanic corrosion after environmental testing. Preliminary results indicated that galvanic coupling enhanced the wedging of substrate by corrosion products when aluminum alloy 6111-T4 (AA 6111-T4) is coupled with cold rolled steel (CRS). In addition, the pitting corrosion of AA 6111-T4 increased when it is coupled with CRS (Figure 1). Although hot dip galvanized (HDG) based galvanic coupons showed no significant wedging by corrosion products, galvanic coupling of CRS with HDG aggravate the scribe creep of HDG. Galvanic isolation methods such as coating before joining or utilizing adhesives significantly reduced galvanic corrosion in the model mixed-material systems. Figure 1. Average pit depth of AA 6111-T4 substrate coupled with different mixed-metal substrates after various exposure times in neutral and acidic cyclic corrosion tests (CCT). Acknowledgements: Research was sponsored by the Army Research Laboratory, the Tank Automotive Research Design Engineering Center, and Drexel University under Cooperative Agreement W911NF-13-2-0046 and related sub awards.

Durability of Low Melt Alloys as Thermal Interface Materials

This study investigates the reliability of low melt alloys (LMAs) containing gallium (Ga), indium (In), bismuth (Bi), and tin (Sn) for the application as Thermal interface materials (TIMs). The analysis described herein involved the in situ thermal performance of the LMAs as well as performance evaluation after accelerated life cycle testing, which included high temperature aging at 130 °C and thermal cycling from −40 °C to 80 °C. Three alloys (75.5Ga & 24.5In, 100Ga, and 51In, 32.5Bi & 16.5Sn) were chosen for testing the thermal performance. Testing methodologies used follow ASTM D5470 protocols and the performance of LMAs is compared with some high-performing commercially available TIMs. Results show that LMAs can offer extremely low (<0.01 cm2 °C/W) thermal resistance compared to any commercial TIMs. The LMA–substrate interactions were explored using different surface treatments (copper and tungsten). Measurements show that depending on the substrate–alloy combinations, the proposed alloys survive 1500 hrs of aging at 130 °C and 1000 cycles from −40 °C to 80 °C without significant performance degradation. The obtained results indicate the LMAs are very efficient as TIMs.

Thermal performance of low melting temperature alloys at the interface between dissimilar materials

This paper describes the thermal performance and practical concerns of using a variety of thermal interface materials (traditional: greases, phase change materials, gels, and thermal pads; emerging: carbon nanotubes, graphene, low melt alloys, and metallic nanosprings) and investigated the reliability of low melt alloys (LMAs) containing gallium, indium, bismuth, and tin as thermal interface materials (TIMs). The analysis presented herein involved the thermal performance evaluation of LMAs placed between different surfaces (copper and nickel) after accelerated life cycle testing, which included high temperature aging at 130 °C and thermal cycling from −40 °C to 80 °C. Three alloys (75.5 Ga and 24.5 In, 100 Ga, and 51 In, 32.5 Bi, and 16.5 Sn) were chosen as candidate LMA TIMs. The testing methodologies followed ASTM D5470 protocols. Measurements showed that the proposed alloys survived as long as 3000 hours of aging at 130 °C and 1500 cycles from −40 °C to 80 °C without significant thermal performance degradation. The obtained results show that the performance of LMAs is significant as TIMs.

Accelerated aging and thermal cycling of low melting temperature alloys as wet thermal interface materials

This paper focuses on developing an effective thermal interface material (TIM) using low melt alloys (LMAs) containing gallium (Ga), indium (In), bismuth (Bi) and tin (Sn). The investigation described herein involved the thermal performance evaluation of LMAs after accelerated life cycle testing, which included isothermal aging at 130°C and thermal cycling from -40°C to 80°C. Three alloys (75.5Ga/24.5In, 100Ga, and 51In/32.5Bi/16.5Sn) were chosen as candidate LMA TIMs. The testing methodologies followed ASTM D5470 protocols and the performance of the alloys was compared to commercially available thermal grease and liquid metal TIMs. To understand the LMA-substrate interactions, the alloys were applied to different surfaces (bare copper, nickel coated copper and tungsten coated copper). It was found that the proposed alloys between bare copper substrates were able to survive as long as 2700h of aging at 130°C and 1400cycles from −40°C to 80°C without significant performance degradation.

Investigation into the application of low melting temperature alloys as wet thermal interface materials

The application of low melt alloys (LMAs) containing In, Ga, Sn, and Bi as compliant high performance thermal interface material (TIM) is investigated. The investigation described herein involves in situ thermal performances of the LMAs as a function of applied pressure and interface temperature, performance evaluation after accelerated life cycle testing, and guidelines to improve the cycle life. Testing methodologies follow ASTM D5470 protocols, and measurements are validated by testing well established, commercially available TIMs and comparisons are made to values reported in open literature as well as manufacturers’ data. Measurement shows that LMAs can offer thermal interfacial resistances as low as 0.005cm2°C/W, and their performance is highly contingent upon the quality of the mating surfaces. The issue of LMA containment and dewetting are discussed along with the solutions to mitigate them.

EMC Management in HEV/EV Applications

EMC Management in HEV/EV Applications

A123 Grid Battery System Single Rack Evaluation

Southern California Edison (SCE) is performing accelerated life cycle testing on a subsystem of A123’s Grid Battery System (GBS). SCE’s laboratory testing is being performed on one rack containing 6 modules that provided 100 kW and 23 kWh. The full GBS is a 2MW 500kWh system composed of 18 racks with 8 modules in each. A test profile composed of 1C and 2C 100% depth of discharge (DOD) cycles was produced to apply 9 cycles per day. Assuming the full system will be used once per day, four months of testing corresponds to the cycles that would be applied over three years of operation. To help track battery performance throughout the testing, Reference Performance Tests (RPTs) are performed every 300 cycles (which corresponds to just over one month). The rack is contained in an environmentally controlled chamber at 20°C during all cycling to simulate the thermal conditions in the GBS container. Over 3000 test cycles have been completed on the GBS system. Approximately 10% decay in capacity has been observed for all power levels. At 80% DOD the available power has decreased only 3%. After approximately the 1200th cycle, a four month pause in testing occurred. Upon restarting the cycling, a significant decrease in capacity was observed. However, the capacity did not decay as quickly. After about the 2000th cycle, the capacity trend resumed the initial rate of decay. This pause in testing has produced interesting conclusions relating to the relationship of calendar life and accelerated cycling which could have significant impacts on electric vehicle or utility application of lithium-ion batteries. This report focuses entirely on the laboratory testing of the GBS single rack. Future analysis will combine these results with those of other SCE tests to produce conclusions regarding the application of the GBS on SCE’s grid.

An Improved Approach to Product Quality Through Testing

Due to the crucial importance of the 1B processor project, AT&T Network Systems (NS) implemented extensive testing programs to ensure that the product delivered was of the highest quality and met customers' needs. In addition to normal customer acceptance testing, the AT&T Network Services Division (NSD) introduced an innovative new strategy called the accelerated life-cycle test program (ALTP) to facilitate the identification and repair of defects. NSD used a 4ESS™ switch having 100-percent reversible traffic to test the retrofit process and to ensure that customer service would not be adversely affected by the introduction of the 1B into the AT&T network. This paper describes the final product integration and verification processes performed by NS, along with the special testing programs established by NSD customers.

Investigating the Effects of Chloramines on Elastomer Degradation

Evaluating elastomer degradation involved an accelerated life cycle testing protocol whereby sets of tension‐mounted coupons were exposed to specific chlorine and ammonia concentrations at elevated temperature. The coupons were inspected regularly for evidence of oxidative degradation and cracking. After a set exposure period, the coupons were assessed for tensile performance, swelling, and surface characterization. With few exceptions, solutions of chloramines produced greater elastomer swelling, deeper and denser surface cracking, more rapid loss of elasticity, and greater loss of tensile strength than equivalent concentrations of free chlorine. Elastomers most susceptible to attack were those formulated with natural or synthetic isoprenes.

Accelerated life cycle testing and analysis for early failure prediction using two types of lead/acid batteries

A sample of 12 small, single cell, lead/acid batteries from each of two manufacturers was subjected to continuous charge—discharge cycling at 50 °C. Reduction of battery capacity to 60% of the manufacturer's rating was the failure criterion. Cycles-to-failure data followed a Weibull distribution, indicating wearout as the failure mode. A Weibull characteristic life of 93 and 580 cycles was found for the cylindrical and flat plate batteries tested, respectively. An early way to detect an inferior battery from among batteries of the same type is suggested. It was found, using an early cycle, that a cell with a comparatively low voltage at end-of-discharge is relatively likely to fail earlier than other batteries of the same type.

Evaluation of materials for artificial heart valves

The heart of a normal human being beats about 38 million cycles every year. An artificial heart valve, to perform at this rate in the adverse conditions inside the heart for 20 years or more, should be highly wear-resistant with excellent fatigue strength. Thus, the study of mechanical and physical properties of the materials intended for use in artificial valves becomes an inseparable part of the valve development process itself. The physical and mechanical requirements of the materials used in the Chitra heart valve have been evaluated by studying their water absorption, adhesive wear and abrasive properties. The mechanical durability of the device has been assessed by accelerated life cycle testing. The test systems developed for the above are described here. The results show UHMW-PE to be a highly wear-resistant material suitable for the occluder. The accelerated wear tests show that the valve with Haynes-25 alloy cage and UHMW-PE disc has durability in excess of 50 years.

Accelerated life cycle tests. Advanced lead-acid cells at elevated temperature

Optimized designs for advanced lead-acid, load-leveling batteries were selected in a limited time period by means of an accelerated life cycle test com