Results Of Accelerated Tests Research Articles

Accelerated ageing of polyurethanes for marine applications

Polyurethanes are frequently used in underwater applications. They are required to resist the marine environment over long periods of immersion but the multiplicity of resin formulations makes material selection difficult. Accelerated tests are essential to guarantee long term integrity. This paper presents results from an experimental study in which polyurethane samples of two hardnesses, 40 and 90 Shore A, have been subjected to immersion in artificial sea water for periods up to two years at temperatures from 50 to 100 °C. In parallel samples have been immersed at sea in the Brest Estuary for up to five years. Mechanical properties have been measured on tensile specimens after ageing. The accelerated test results and FTIR analysis indicate that hydrolysis can occur. However, an estimation based on a linear Arrhenius extrapolation indicates that the timescale for 50% property loss at sea temperatures is in excess of 100 years. The results from sea ageing confirm that these materials retain 100% of their initial tensile properties after five years of immersion.

Study on Gas Fastness of Ink Jet Prints

Actual environment factors such as O3, NO2, SO2, temperature, and humidity in ordinary homes and offices were measured. Color density on Inkjet and Silver halide digital photo images under such environment were traced and how such environmental factors multiply lay impact on each digital images were discussed.The discussion was made in relation with acceleration test results and made based on multiple regression analysis. Both of the discussion results show that the fadings on digital images are caused by number of gas factors such as O3, NO2, and SO2 according to the color. Mixed gas acceleration test using O3, NO2, and SO2 gases represents the actual color-fading more accurately than the single O3 gas test.To simulate the accurate and fair lifetime of gas fastness of various digital photo images, mixed gas test, including O3, NO2, and SO2 is more appropriate.

Friction and Wear with Surface Melting at High Sliding Speed and High Contact Pressure (1st Report,An Experimental Approach to the Condition of the transition to a Melting Lubrication)

Based on the recent demands for higher sliding velocity of components, the excessive wear of the slider due to it has been discussed. However, since R. S. Montgomery reported his experimental work on the wear at high sliding speeds, no one has reported theoretical analysis of the slider wear. In this study, the frictional resistance was examined with static intrusion and dynamic acceleration tests. In the static intrusion test, the static frictional resistance increases linearly as the slider travel increase until the slider come to fully contact the cylinder. Meanwhile, the dynamic acceleration test revealed that the dynamic frictional resistance is about 30-40% of the static one with the slider travel up to approximately 50 mm, and that it then falls to the level of about 10% as the slider travel further increases. Such the sudden change corresponds to the estimated values of the friction coefficient : the friction coefficient estimated from the dynamic acceleration test results is about 0.1 in the earlier stage and falls to about 0.03 in the later stage, while the static intrusion test results only show a constant coefficient value of about 0.3. This drastic reduction of the friction coefficient in the dynamic test is considered to be attributable to the surface liquefaction of the slider material, where a melting lubrication may occur. The transitional condition to such a melting lubrication can be quantitatively expressed and evaluated by means of the melting lubridcation index, BLI.

Vestibular neuronitis in pilots: follow-up results and implications for flight safety.

OBJECTIVES To report our experience over the past 12 years with the evaluation and follow-up of pilots with vestibular neuronitis and to discuss points relevant to flight safety and the resumption of flying duties. STUDY DESIGN A retrospective, consecutive case series.METHODS Eighteen military pilots with vestibular neuronitis were examined and followed up. A complete otoneurological workup was performed, including both physical examination and laboratory evaluation. The latter included electro-oculography (EOG) and a rotatory chair test using the smooth harmonic acceleration protocol. RESULTS The mean patient age was 35 +/- 6 years (range, 23 to 42 y), and the average follow-up period was 20.5 +/- 12.8 months (mean +/- standard deviation [SD]; (range, 11 to 48 mo). Electro-oculography caloric test on presentation documented significant unilateral hypofunction in all patients. Thirteen of the 18 patients (72%) had abnormal smooth harmonic acceleration test results. None of the pilots reported any symptoms on follow-up. However, five (28%) had positive otoneurological examination findings, and eight (44%) still had significant caloric lateralization (>25%). The average caloric hypofunction was reduced from 67.8% +/- 29.3% at onset to 40% +/- 16% (mean +/- SD, <.05, paired test). Seven of the patients (39%) had additional electro-oculography findings beyond caloric hypofunction. These included spontaneous, positional, and positioning nystagmus. Smooth harmonic acceleration disease on follow-up was documented in eight patients (44%), five of whom had canal paresis. Eleven patients (61%) demonstrated residual vestibular damage on follow-up. In 6 of these 11 cases (55%), the laboratory evaluation revealed vestibular deficits otherwise undiagnosed by the bedside test battery. CONCLUSIONS The vestibular system plays a central role in orientation awareness and is often challenged by flying conditions. The finding that approximately 60% of pilots who have had vestibular neuronitis continue to show signs of vestibular malfunction, despite apparent clinical recovery, emphasizes the need for a complete vestibular evaluation, including specific bedside testing and laboratory examinations, before flying duties can be resumed.

Interpreting weathering acceleration factors for automotive coatings using exposure models

A number of exposure models have been developed to account for the variation in photo-oxidation rate with light intensity, wavelength distribution, temperature and humidity. These models have proven useful in accounting for the different observed rates of photo-oxidation and other weathering phenomena in different outdoor locations. In this paper, the same models are applied to calculate acceleration factors of various accelerated weathering tests relative to standard outdoor Florida weathering. The predicted acceleration factors are in reasonable agreement with the ranges commonly observed for various accelerated tests. The models also can be used to assess the sensitivity of the acceleration factors to material differences and to variations in environmental conditions within a given chamber and from chamber-to-chamber. The critical importance of variability to the reproducibility and reliability of accelerated test results are discussed. Difficulties of comparing measurements made outdoors with values for accelerated tests are also discussed. Of particular note is the need for all exposures to measure and report actual sample temperatures rather than air or black panel temperatures.

Thermomechanical Durability Analysis of Flip Chip Solder Interconnects: Part 2—With Underfill

The effect of underfill material on reliability of flip chip on board (FCOB) assemblies is investigated in this study by using two-dimensional and three-dimensional finite element simulations under thermal cycling stresses from −55°C to 80°C. Accelerated testing of FCOB conducted by the authors reveals that the presence of underfill can increase the fatigue durability of solder interconnects by two orders of magnitude. Similar data has been extensively reported in the literature. It is the intent of this paper to develop a generic and fundamental predictive model that explains this trend. While empirical models have been reported by other investigators based on experimental data, the main drawback is that many of these empirical models are not truly predictive, and can not be applied to different flip chip architectures using different underfills. In the proposed model, the energy-partitioning (EP) damage model is enhanced in order to capture the underlying mechanisms so that a predictive capability can be developed. A two-dimensional finite element model is developed for stress analysis. This model accounts for underfill over regions of solder in an approximate manner by using overlay elements, and is calibrated using a three-dimensional finite element model. The model constant for the enhanced EP model is derived by fitting model predictions (combination of two-dimensional and three-dimensional model results) to experimental results for a given temperature history. The accuracy of the enhanced EP model is then verified for a different loading profile. The modeling not only reveals the influence of underfill material on solder joint durability, but also provides the acceleration factor to assess durability under life cycle environment, from accelerated test results. Experimental results are used to validate the trends predicted by the analytical model. The final goal is to define the optimum design and process parameters of the underfill material in FCOB assemblies in order to extend the fatigue endurance of the solder joints under cyclic thermal loading environments.

Performance Evaluation of Multi-Fuel Spark Ignition Engines

An experimental investigation was conducted on a spark ignition engine using Gasoline and CNG . The aim is to compare the effects of both fuels on the steady and transient performance of the engine as well as the exhaust emission characteristics . A complete facility for the testing was constructed and operated. The test rig includes, besides the 1.301 litre spark ignition engine and the Heenan hydraulic type dynamometer, all instrumentation necessary for evaluating engine steady and transient performance, and exhaust pollution characteristics. The test rig was also furnished with computer controlled data acquisition systems. It was concluded that using CNG increases the brake specific fuel consumption and decreases the volumetric efficiency, brake thermal efficiency, and exhaust gas temperature. It also increases CO concentration in the exhaust gases at full loads but slightly decreases it at part loads. The propane and methane hydrocarbon emissions are increased with CNG at all engine operating conditions . The mixture equivalence ratio studied has the greatest influence on engine performance and emission. The transient acceleration test results showed that using CNG decreases engine response to a sudden acceleration than using gasoline. The transient load acceptance test results showed that using CNG decreases the ability to overcome the sudden load than gasoline.

Methodologies for lifetime predictions of rubber using Arrhenius and WLF models

The WLF approach is appropriate for lifetime predictions when polymer ageing is controlled by a viscoelastic process (relaxation, creep). This methodology using time/temperature shift will be illustrated by the creep of SBR/NR. When physico-chemical mechanisms are dominant, the Arrhenius approach is the most widely used for evaluating accelerated test results involving the effect of temperature. Service lifetimes have been estimated for the thermal ageing of NBR/PVC and for the ageing of HNBR in gaseous fluids. Predictions using the Arrhenius model usually do not take into account oxygen-diffusion-controlled oxidations. In the case of the thermal ageing of EPDM, extrapolations are determined by the heterogeneity of the oxidative ageing of bulk polymer samples.

Methodologies for lifetime predictions of rubber using Arrhenius and WLF models

The WLF approach is appropriate for lifetime predictions when polymer ageing is controlled by a viscoelastic process (relaxation, creep). This methodology using time/temperature shift will be illustrated by the creep of SBR/NR. When physico-chemical mechanisms are dominant, the Arrhenius approach is the most widely used for evaluating accelerated test results involving the effect of temperature. Service lifetimes have been estimated for the thermal ageing of NBR/PVC and for the ageing of HNBR in gaseous fluids. Predictions using the Arrhenius model usually do not take into account oxygen-diffusion-controlled oxidations. In the case of the thermal ageing of EPDM, extrapolations are determined by the heterogeneity of the oxidative ageing of bulk polymer samples.

Dynamic life-estimation of CMOS ICs in real operating environment: precise electrical method and MLE

The functionality of an IC in field use can be maintained by replacing an IC shortly before its anticipated failure. An accurate estimation of circuit lifetime is important in selecting a replacement time to: (1) avoid unanticipated circuit failure by replacing them as early as possible; and (2) use the IC fully by replacing them as late as possible. Since the problem is different from lifetime estimation with accelerated test results, this approach continually measures circuit performance and then analyzes the measurements statistically. The whole estimation process is covered from selection of circuit parameters for performance measurement to development of an aging model for the statistical analysis. The circuit-delay change due to hot-carrier effects is selected to quantify the performance degradation; an aging model, founded on the hot-carrier induced failure mechanism, is developed. Maximum likelihood estimation (MLE) is used for the statistical characteristics of future aging, where the severity of the operating environment is assumed to be a stationary random process. The MLE are used to choose an efficient time for IC replacement. The practical use of the suggested method in IC maintenance is demonstrated with statistically simulated data.

Accelerated testing for cosmic soft-error rate

This paper describes the experimental techniques which have been developed at IBM to determine the sensitivity of electronic circuits to cosmic rays at sea level. It relates IBM circuit design and modeling, chip manufacture with process variations, and chip testing for SER sensitivity. This vertical integration from design to final test and with feedback to design allows a complete picture of LSI sensitivity to cosmic rays. Since advanced computers are designed with LSI chips long before the chips have been fabricated, and the system architecture is fully formed before the first chips are functional, it is essential to establish the chip reliability as early as possible. This paper establishes techniques to test chips that are only partly functional (e.g., only 1Mb of a 16Mb memory may be working) and can establish chip soft-error upset rates before final chip manufacturing begins. Simple relationships derived from measurement of more than 80 different chips manufactured over 20 years allow total cosmic soft-error rate (SER) to be estimated after only limited testing. Comparisons between these accelerated test results and similar tests determined by “field testing” (which may require a year or more of testing after manufacturing begins) show that our experimental techniques are accurate to a factor of 2.

Polymer-Modified Asphalt Pavements in Ontario: Performance and Cost-Effectiveness

Two trial sections were constructed to investigate the rutting resistance and low temperature performance of different polymer-modified asphalt (PMA) mixes at sites representative of highways experiencing rutting as a result of heavy traffic loading in cold climatic regions. The two-way average annual daily traffic for both sites was &gt;35,000 (6,000 vehicles per day). Modified asphalts used in the trial sections include engineered bitumen type 306, premium asphalt, reprocessed polyethylene (Novophalt), Neoprene, scrap tire rubber, Vestoplast-S, Kraton 4460, Styrelf, and polyethylene. Representative test samples of aggregates, asphalt cement, modified asphalts, and hot mixes were taken for routine testing during production. In situ quality control tests were done by taking plate samples while laying the mix and by coring after compaction. Additional laboratory tests were done at temperatures ranging from 0°C to —35°C to evaluate the materials’ low temperature cracking resistance. Field performance of trial sections was monitored yearly by crack mapping and measuring transverse profiles at 30-m spacing on each test section. Levels were taken at 100-mm intervals by using a dipstick. A computer program was written to process the data and calculate the rut depths for each wheelpath. Crack mapping was done to assess the crack growth in each test section. The performance of the sections was compared with respect to average rut depth and crack growth. The following are described: (a) the modified mix design chosen specifically to produce accelerated test results, (b) the experience gained in the construction of trial sections, (c) the results of laboratory testing to evaluate the low temperature performance of the PMAs, (d) the field performance evaluation with respect to rutting and cracking, and (e) the life cycle cost analysis. Average rut depth measurements 5 to 7 years after construction show that PMA pavement sections are performing better than conventional asphalt with respect to rutting. With regard to cracking, polymers with 85 to 100 penetration (pen) base asphalt did not perform better than control sections. However, there is an indication that PMA, which has a soft grade (150 to 200 pen) base asphalt, tends to improve low-temperature performance comparable to the control section. In other words, PMA generally performs better than conventional asphalt, provided it contains a soft grade (150 to 200 pen) base asphalt. Life cycle cost analysis indicates that PMA is cost-effective in extending pavement life by 2 to 3 years if the cost of polymer modification does not exceed the cost of conventional asphalt by 100 percent.

Abrasion Resistance of High-Strength Concrete Made with Class C Fly Ash

This work was performed to evaluate the abrasion resistance of concrete proportioned to have five levels of cement replacements (15, 30, 40, 50, and 70 percent) with one source of Class C fly ash. A reference concrete without fly ash was proportioned to have a 28-day compressive strength of 41 MPa. Concrete specimens were subjected to abrasion according to the American Society for Testing and Materials (ASTM) C 944 test method. In this work, all concretes made with and without fly ash passed the abrasion resistance requirements per ASTM C 779, Procedure C. Depth of wear values produced by the ASTM C 944 test were quite low for the strength levels tested in this work. An accelerated test method was developed and used to evaluate the abrasion resistance of high-strength concrete. This method used grinding wheels with smaller washers, and a standard Ottawa sand was applied to the surface being abraded at intervals of 1 minute. Accelerated test results revealed that the abrasion resistance of concrete having cement replacement up to 30 percent was comparable to the reference concrete without fly ash. Beyond 30 percent cement replacement, fly ash concrete displayed slightly lower resistance to abrasion relative to non-fly ash concrete.

Approaches to testing the durability of materials used in the construction and maintenance of buildings

This paper summarizes the factors involved and approaches taken when testing the durability of construction materials. The problems associated with current standards are put into context and an approach for the formulation of future standards is recommended. This paper is to be used as a working document for the subcommittee on ‘Design of short term test methods’ of the RILEM 140-TSL/CIB W80 on the design life of buildings. The recommended approach would enable the response of materials to any environment to be modelled, a consequence of which would be more accurate service-life prediction. In addition this would provide a better understanding for improving material quality. Critical steps for this approach include: (i) consideration of the factors which might affect the durability; (ii) accelerated testing to define the most significant factors causing degradation, and the mechanism of that degradation; (iii) evaluation of the significant causes of degradation in the proposed end use environment; (iv) construction of models and damage functions for the material's response to the environment based on the accelerated test results and the environmental measurements.

Oxidative effects of ozone on the aging of structural silicone elastomers

AbstractThe changes in the physical properties of three different commercial silicone sealants used in structural glazing applications were monitored as a function of various aging factors. The variables included, simultaneous exposure to ozone and moisture in which the pH of the moisture was maintained at discrete levels of 3 and 11. The extremes of the pH range represent recorded values for acid rain (pH = 3) and basic cleaning solutions (pH = 11), respectively. A second portion of the study involved studying the effect of loading on the sealant performance. The experimental coupons were cut from cast sheets of DC‐790, DC‐995, and DC‐983. An Instron tester was used to measure the changes in the engineering properties such as Young's modulus, relaxation time, and ultimate tensile stress of the test samples as a function of time of exposure to the different variables. Unexposed samples, kept at ambient laboratory conditions, were used as the control. Results of these tests indicate that the Young's modulus of the samples decreases during an initial period as a result of their exposure. After this initial decrease the sample moduli showed a steady increase with time. Surface cracking was observed during the initial period, even though the moduli continued to increase. Moreover, the acid and ozone appear to act synergistically in the deterioration of the sealant. Samples exposed to the higher pH level did not show this kind of behavior. The effect of tensile loading on the sealant was significant only for DC‐983, the high modulus formulation. This was perhaps because of the creation of high stress centers. The medium modulus material exhibited good resistance to the synergistic effects causing deterioration. Ozone resulted in discoloration, softening, and change in structure in the low modulus formulation. Although the ozone did not react aggressively with silicone, its slow attack or degradation should still be of concern. In spite of the use of inhibitors, severe and acute cracks appeared on the surface of the rubber material at angles of ninety degrees across the line of tension. It is hoped that these accelerated test results can lead to more informed decisions concerning silicone sealant life following their exposure to ozone and acid precipitation. © 1994 John Wiley &amp; Sons, Inc.

Abrasion resistance of concrete as influenced by inclusion of fly ash

This research was conducted to evaluate abrasion resistance of high-volume fly ash concrete. A reference plain portland cement concrete was proportioned to obtain 28-day strength of 41 MPa. Concrete mixtures were also proportioned to have two levels of cement replacements (50 and 70%) with an ASTM Class C fly ash. Abrasion tests were carried out using the rotating cutter method as per ASTM C-944. In this work all the concrete specimens made either with or without fly ash passed the abrasion resistance requirements per ASTM C-779, Procedure B. An accelerated test method was also developed to evaluate abrasion resistance of concrete. This method used the rotary cutter device having dressing wheels equipped with smaller size washers. A measured amount of standard Ottawa sand was added to the surface being abraded at one minute intervals. The accelerated test results exhibited lower abrasion resistance for high-volume fly ash concrete systems relative to no-fly ash concrete.

Clinical Value of Sinusoidal Harmonic Acceleration Test Results: Site of Lesion and Side of Lesion

Sinusoidal harmonic acceleration tests can be used reliably to determine site and side of lesion. Results from 6000 patients collected over the past 10 years have shown that the temporal pattern of asymmetry can be reliably used to differentiate peripheral from central vestibular dysfunction. Peripheral cases tend to have a high level of asymmetry, with temporal regression to normal range, and a high correlation with patient symptoms. Central cases tend to have a low level of variable asymmetry and variable symptoms. In either case, phase can be abnormal or normal and cannot be reliably used to differentiate peripheral from central dysfunction. By combining phase and symmetry, the side of the lesion can be reliably determined. When phase is abnormal, asymmetry is toward the side of the lesion in 92 per cent of cases, whereas when phase is normal, asymmetry cannot be reliably used to determine side of lesion. SHA testing has contributed significantly to our clinical ability to fully evaluate the vestibular system and has become an indispensable part of the complete vestibular laboratory. It requires a relatively large patient load as well as software and hardware support to become a cost-effective utility.

Accelerated Thermal Fatigue Cycling of Surface Mounted PWB Assemblies in Telecom Equipment

Telecom equipment is subject to thermal cycles caused by both variations in temperature between day and night and variations in the telephone traffic. To simulate such thermal excursions, accelerated thermal cycle testing between — 10°C and 100°C has been established as a standard method within Ericsson Telecom. Thermal cycle tests have been carried out for frequencies ranging from one cycle per day to 30 cycles per hour in order to cover the different thermal excursions that occur in telecom equipment. It has been found that the life of a surface mounted PWB assembly can be predicted from the accelerated testing results using a frequency modified Coffin‐Manson relation. Factors which influence the fatigue life of solder joints such as solder material, compliant leads, compliant surface layers and mismatch between package and board are discussed. Based on results from accelerated testing it is suggested that the optimal PWB design for leadless ceramic chip carriers should be a moderate TCE matching combined with a compliant surface layer.

Distributed energy store (DES) railgun development

Over the past four years LTV Aerospace and Defense Company [LTVAD) has operated on a regular basis two high-energy electromagnetic (EM) railguns with over 200 shots, 100 firings since the last EM launcher technology symposium, making this to our knowledge the most productive launcher laboratory in the nation. The development work has focused on launcher efficiency, projectile compatibility, and barrel material life improvements. The 20 mm DES launcher has also become known as a workhorse for hypervelocity kinetic energy lethality experiments, operating in the velocity range of 2 to 6 km/sec. This paper describes the recent LTVAD EM Propulsion Laboratory developments and improvements with the DES launcher, power supply, controls, instrumentation, and ballistic range. Results on DES launcher efficiency optimization with factors greater than 2 over breech fed railguns are presented. Methods of tailoring the launch acceleration force and test results are discussed.

Reliability of Liquid Crystal Display

This paper reports the reliability of twisted nematic liquid-crystal display for basic applications such as watches and calculators. We have studied significant stress factors such as voltage, temperature and humidity, and their corresponding failure modes. The main failure mode is LCD misalignment; many different modes appear corresponding to different stress conditions as well as material and process for the LCD. We have analyzed the accelerated test results by Weibull distribution, elucidated accelerating factors, and estimated life time. The life is inversely proportional to 1.78-2.45 power of applied voltage, depending upon misalignment modes. The distribution of life is well expressed by Weibull distribution with shape parameter between 2.5-3.0, and proportional to the square of coefficient of variation of life. We conclude that the acceleration factors could be determined and 99.9% of tested displays will live more than 10 years. The knowledge on reliability of LCD can be now applied to new fields of LCD, such as industrial use, home appliance, and automotive instruments.