Short-term Test Data Research Articles

Rationalization of Creep Data of Creep-Resistant Steels on the Basis of the New Power Law Creep Equation

The conventional power law creep equation (Norton equation) relating the minimum creep rate to creep stress and temperature cannot be used to predict the long-term creep strengths of creep-resistant steels if its parameters are determined only from short-term measurements. This is because the stress exponent and activation energy of creep determined on the basis of this equation depend on creep temperature and stress and these dependences cannot be predicted using this equation. In this work, it is shown that these problems associated with the conventional power law creep equation can be resolved if the new power law equation is used to rationalize the creep data. The new power law creep equation takes a form similar to the conventional power law creep equation but has a radically different capability not only in rationalizing creep data but also in predicting the long-term creep strengths from short-term test data. These capabilities of the new power law creep equation are demonstrated using the tensile strength and creep test data measured for both pipe and tube grades of the creep-resistant steel 9Cr-1.8W-0.5Mo-V-Nb-B (P92 and T92).

Creep behavior and modeling of neat, talc-filled, and short glass fiber reinforced thermoplastics

Abstract Creep behavior of neat, talc-filled, and short glass fiber reinforced injection molded thermoplastic composites were investigated and modeled at room and elevated temperatures. Creep strength decreased and both creep strain and creep rate increased with increasing temperature. The temperature effect was more significant for samples with glass fibers in the transverse to the load direction, as compared with the longitudinal direction. The Larson–Miller parameter was able to correlate the creep rupture data of all materials. The Monkman–Grant relation and its modification were successfully used to correlate minimum creep rate, time to rupture, and strain at rupture data. The Findley power law and time–stress superposition principle (TSS) were used to represent nonlinear viscoelastic creep curves. Long-term creep behavior was also satisfactory predicted based on short-term test data using the TSS principle.

Effects of plastic pre-straining level on the creep deformation, crack initiation and growth behaviour of 316H stainless steel

The effects of the material pre-straining level, in the form of plastic pre-compression at room temperature, on the tensile, creep deformation, creep crack initiation and growth behaviour of 316H stainless steel have been examined at 550 °C. Experiments have been performed on the 4%, 8% and 12% pre-compressed specimens and the results are compared with existing data on the pre-compressed material to investigate the change in mechanical response, creep failure, creep crack initiation and growth behaviour of 316H over a range of plastic pre-straining levels. Comparisons are also made to short term and long term test data on the as-received material. It has been found that creep ductility and rupture times decreased with an increase in pre-strain levels considered. The test results obtained from different material states are discussed in terms of the influence of material pre-straining level on the microstructural deformation, mechanical response, creep deformation and crack growth behaviour of the material.

Application of time-temperature-stress superposition principle on the accelerated physical aging test of polycarbonate

The effect of physical aging on the polymer mechanical properties is very important for long-term safety assessment of engineering application. In this paper, the physical aging tests of polycarbonate (PC) were conducted systemically under different temperature and uniaxial tensile stress level. It was shown that both temperature and stress have obvious accelerated effect on the physical aging of PC. The higher the temperature and stress level are, the faster the aging process is. To predict the long-term behavior after physical aging using the short-term test results of PC, the elongation-at-break was chosen as the index of the severity of physical aging. An Arrhenius-type time–temperature–stress superposition principle (TTSSP) was proposed to evaluate long-term performance using short-term test data. Using the proposed method, time and cost can be dramatically reduced for the assessment of long-term physical aging performance of polymeric material. POLYM. ENG. SCI., 55:2215–2221, 2015. © 2015 Society of Plastics Engineers

A Simple and Reasonable Calculation Equation of Balanced Fertilization

Reasonable fertilization is a primary concern for agronomy scientists and farmers. However, there is still no satisfying calculation formula to guide farmer’s fertilizing. Five kinds of indices were tested in more than 500 field plots successively, and more than 50 pieces of long-term and short-term fertilizer field test data acquired by others were analyzed. Quick-acting fertilizers should be applied for balanced fertilization if the soil-available nutrient content is within the normal range. Through rigorous derivation and validation by a multi-year continuous 15N tracer field test, it is obtained that, total soil exogenous N = total output N − total recovery N + soil profit or lost N; utilization efficiency of fertilizer N = (output N − exogenous N) ÷ balanced application amount of N fertilizer. Optimal balanced utilization efficiency of fertilizer N, P, K = total recovery efficiency, and soil nutrient net amount = total amount after test − total amount before test. Equation application parameters were collected from more than 50 tests, which is more applicable than collecting from a single test. When soil-available nutrient content is excessively low or excessively high, adjusting this should be based on balanced fertilization to properly increase or reduce the fertilization rate.

The influence of pre-compression on the creep deformation and failure behaviour of Type 316H stainless steel

The influence of pre-compression to 8% plastic strain at room temperature has been examined on the tensile properties, uniaxial creep deformation, creep crack initiation and growth behaviour of Type 316H stainless steel at 550°C. Uniaxial creep and crack growth tests have been performed on the pre-compressed (PC) material and the results compared to existing long term (>15,000h) and short term test data on as-received (AR) (i.e. uncompressed) material. Pre-compression has been found to increase the materials subsequent yield stress in tension. Therefore the extent of non-linearity observed on the load–displacement curves of uniaxial creep rupture and crack growth tests on PC material is limited compared to AR material. In addition pre-compression causes a significant reduction in creep ductility and rupture time, although similar average and minimum creep strain rates are found in PC and AR materials. The creep crack growth (CCG) data on PC and AR materials have been characterised using the steady state creep C* parameter employing appropriate validity criteria and geometry dependent fracture mechanics parameter solutions. The CCG results are compared to the creep crack growth prediction models. Based on the creep properties, creep ductility and metallurgical observations of the fracture behaviour of the AR and PC materials, it has been shown that short term creep crack growth tests on PC material may be used to predict long term creep crack initiation (CCI) and CCG behaviour of AR material at 550°C.

Development of novel steam-turbine high-chromium steels with enhanced stability of long-term strength characteristics

The basic alloying principles of novel heat-resistant steels for steam-turbine equipment and also the trends in provision of their long-term strength are considered. Two tentative steel compositions of martensite class with a chromium content of 9–12% and low content of hydrogen are developed. On the basis of comparatively short-term test data, the possibility, in principle, to provide long-term strength for novel heat-resistant materials on the order of 100 MPa on a base of 200000 h has been shown.

Creep and stress-rupture of Nafion® membranes under controlled environment

Nafion® as a polymer shows time-dependent behavior including creep and relaxation. Application of this material in automotive fuel cells and targeted lifetimes require consideration of time-dependent failure of Nafion® in fuel cell design. In this work, creep tests for Nafion® were conducted in a controlled environment at different hydrations and temperatures. Stress-rupture curves for Nafion® were obtained for different hydrations (RH = 5%, 50% and 90%) at room temperature and also for two different temperatures (25 °C & 80 °C) at 50% relative humidity. Time-dependent failure was observed for all these conditions regardless of temperature and hydration level (state of water in Nafion®). Ionic forces created by cross linkings (by introducing water to membrane) do not seem to prevent disentanglements of the chains since there is no change in rate of time-dependent failure results. A time-hydration/temperature equivalence method (Sherby–Dorn) is suggested as a method to use short-term test data to estimate rupture times for other conditions.

Influence of moisture absorption on creep of GRP composite pipes

The aim of this work was to study the influence of moisture absorption on long-term creep behavior of composite pipes. These pipes are used in water transportation which has an effect on the mechanical properties and on the polymeric composite matrix. Glass-reinforced thermosetting plastics (GRP) pipes are typically tested under ring deflection and/or internal pressure conditions. In this study, experimental creep data obtained from standard test methods under ring deflection conditions were used. This loading configuration simulates in the laboratory the external loads induced in a sub-soil installation. The creep tests were performed on unconditioned and preconditioned specimens. Long-term mechanical behavior prediction based on short-term test data is necessary for design. For this purpose dynamic mechanical thermal analysis (DMTA) tests were performed on specimens machined from GRP pipes. Ten specimens were tested as delivered. Another 10 specimens were conditioned in water at room temperature and another 10 were conditioned in water at 50 ∘ C , until saturation. The time–temperature superposition principle (TTSP) and extrapolation using a power law relation were applied to DMTA data for long-term creep prediction. Both methods were found to be conservative, i.e. predict higher stiffness reduction than the creep tests. Although creep tests were quite dissimilar from the DMTA tests, extrapolation using a power law relation appeared to be accurate enough to be used as a predictive tool for project design. Finally, comparisons of the DMTA data for different environment conditioning enabled the assessment of the hygrothermal effects on modulus.

Use of an SF6-Based Diagnostic Tool for Assessing Air Distributions and Oxygen Transfer Rates during IAS Operation

A diagnostic test designed to assess air distribution and oxygen delivery rate to the aquifer during in situ air sparging (IAS) is described. The conservative tracer gas, sulfur hexafluoride (SF6), is added upstream of the air injection manifold during steady IAS operation and groundwater samples are collected from the target treatment zone after some time period (usually 4 to 24 h). The appearance of SF6 in groundwater is used to characterize the air distribution in the target treatment zone, while the SF6 concentration increase with time is used to assess oxygen transfer rates to the target treatment zone. Conversion from SF6 concentration to oxygen mass transfer rate involves correcting the SF6 concentration increase over time for differences in the relevant chemical properties and injection air concentration. Data presented from a field demonstration site illustrate the utility of this test for identifying air distribution details not readily identified by deep vadose zone helium and groundwater pressure transducer response tests. Oxygen transfer rates at this site ranged from 0 to 20 mg-O2/L-H2O/d. Finally, a comparison of short-term SF6 test data with longer-term dissolved oxygen data illustrated this test's utility for anticipating long-term dissolved oxygen distributions.

Genetic toxicology data in the evaluation of potential human environmental carcinogens.

In 1969, the International Agency for Research on Cancer (IARC) initiated the Monographs Programme to evaluate the carcinogenic risk of chemicals to humans. Results from short-term mutagenicity tests were first included in the IARC Monographs in the mid-1970s based on the observation that most carcinogens are also mutagens, although not all mutagens are carcinogens. Experimental evidence at that time showed a strong correlation between mutagenicity and carcinogenicity and indicated that short-term mutagenicity tests are useful for predicting carcinogenicity. Although the strength of these correlations has diminished over the past 20 years with the identification of putative nongenotoxic carcinogens, such tests provide vital information for identifying potential human carcinogens and understanding mechanisms of carcinogenesis. The short-term test results for agents compiled in the EPA/IARC Genetic Activity Profile (GAP) database over nearly 15 years are summarized and reviewed here with regard to their IARC carcinogenicity classifications. The evidence of mutagenicity or nonmutagenicity based on a 'defining set' of test results from three genetic endpoints (gene mutation, chromosomal aberrations, and aneuploidy) is examined. Recommendations are made for assessing chemicals based on the strength of evidence from short-term tests, and the implications of this approach in identifying mutational mechanisms of carcinogenesis are discussed. The role of short-term test data in influencing the overall classification of specific compounds in recent Monograph volumes is discussed, particularly with reference to studies in human populations. Ethylene oxide is cited as an example.

Characterization of Pile Capacity with Time in the Cooper Marl: Study of Applicability of a Past Approach To Predict Long-Term Pile Capacity

The Cooper Marl is a massive geological group, consisting of stiff, cohesive calcareous soils, which serves as the bearing stratum for the large majority of deep foundations in the Charleston, South Carolina, area. It has long been recognized that piles driven into the material experience tremendous setup, or capacity gain with time. Numerous driven piles that bear within the Cooper Marl have been statically or dynamically tested at various times after installation. This pile-testing database has been used to backcalculate the coefficients of a logarithmic expression ( Q/Q0 - 1 = Alog t/t0) that predicts pile capacity gain with time. For the largest data set, composed of 305-mm (12-in.) prestressed concrete (PSC) piles, the calculated coefficients are fairly similar, which seems to support the viability of the method and use of the equation. By using the calculated coefficients, long-term pile capacity of 305-mm (12-in.) PSC piles driven into the Cooper Marl should be able to be predicted based on the results of short-term restrike or load test data. The data also indicate that the coefficients of the expression are dependent on the pile size and that the rate of the capacity gain with time generally decreases as the pile size increases.

Future approaches to genetic toxicology risk assessment

Short-term genetic toxicology tests were developed for the purpose of identifying chemical carcinogens in the environment. After two decades of development and validation, the tests are well-established in routine testing schemes, but our views of their utility for safety evaluation have undergone re-assessment. The correlation between identified mutagens and identified carcinogens has turned out to be significantly less than one. Processes or mechanisms that are not directly genotoxic appear to play a role in carcinogenesis. While short term test data are still components of the assessment of carcinogenic risk, genetic damage also has been recognized as important in its own right, in relation to heritable genetic risk and other health-related effects, such as aging, reproductive failure and developmental toxicity. The revolution in molecular biology and genetic analysis occurring over the past 20 years has contributed to the wealth of new information on the complexities of cell regulation, differentiation, and the carcinogenic process. These technologies have provided new experimental approaches to genetic toxicology assessments, including transgenic cell and animal models, human monitoring, and analysis of macromolecular interactions at environmentally relevant exposures. The potential exists for the development of more efficient and more relevant genetic toxicology testing schemes for use assessing human safety. A delineation of contemporary needs, a modern view of the elements of cancer induction, and an examination of new assays and technologies may provide a framework for integrating new approaches into current schemes for evaluating the potential genetic and carcinogenic risk of environmental chemicals.

Design rated oriented strandboard in CSA standards

The 1994 edition of CSA (Canadian Standards Association) Standard 086.1 "Engineering design in wood" includes, for the first time, specified strength and stiffness for design rated oriented strandboard (OSB). Design rated OSB panels are manufactured in accordance with the new CSA Standard 0452. In this paper, the results of the short-term (1–10 min) test data which led to the establishment of the three rating grades of Type 1 (standard) design rated OSB are presented. In addition, factors that may affect the classification such as panel thickness and orientation are discussed. Key words: OSB, waferboard, structural panels, wood.

Modeling of Oxidative Aging Behavior of Asphalts from Short-Term, High-Temperature Data as a Step Toward Prediction of Pavement Aging

The oxidative aging data collected during the Strategic Highway Research Program have been analyzed in terms of kinetics of viscosity change with time and temperature. Changes in viscosity have been used as the measure of the progress of aging. The objective is to model viscosity increases accurately enough to be able to predict aging (in terms of viscosity changes) at pavement temperatures from short-term test data acquired at high temperature. This involved constituting a mathematical model, based on oxidative reactions, and a nonlinear regression of the data to test predictability of the proposed model. Clearly, there is a point beyond which viscosity change becomes independent of time, but no data were collected to that extent. Separately, it has been shown that oxidation of aliphatic sulfide to sulfoxide and oxidation of benzylic carbon to carbonyl are the principal chemical reactions that contribute to an increase in viscosity. The data fit the proposed equation sufficiently well to allow calculatio...

Modeling of Oxidative Aging Behavior of Asphalts from Short-Term, High-Temperature Data as a Step toward Prediction of Pavement Aging

The oxidative aging data collected during the Strategic Highway Research Program have been analyzed in terms of kinetics of viscosity change with time and temperature. Changes in viscosity have been used as the measure of the progress of aging. The objective is to model viscosity increases accurately enough to be able to predict aging (in terms of viscosity changes) at pavement temperatures from short-term test data acquired at high temperature. This involved constituting a mathematical model, based on oxidative reactions, and a nonlinear regression of the data to test predictability of the proposed model. Clearly, there is a point beyond which viscosity change becomes independent of time, but no data were collected to that extent. Separately, it has been shown that oxidation of aliphatic sulfide to sulfoxide and oxidation of benzylic carbon to carbonyl are the principal chemical reactions that contribute to an increase in viscosity. The data fit the proposed equation sufficiently well to allow calculation of rate constants of viscosity increases for both reactions, and, hence, allow development of an Arrhenius temperature relationship. Finally, it is hoped that the proposed equation will provide reasonable estimates of rates of oxidative aging of asphalts at pavement temperatures from short-term, high-temperature oxidative aging data measured in a laboratory.

Comparison of electrical aging tests on epr-insulated minicables and ribbons from full-sized EPR cab

The results of electrical endurance tests performed on ribbons cut from full-sized EPR cables are compared with those obtained by tests performed on cable models, having the same insulation as the full-sized cable. It is shown that the voltage endurance coefficient estimated on the basis of the short-term life test data has approximately the same value for cable models and ribbons, according to both inverse-power and exponential models. However, the surface roughness resulting from cutting the specimens can affect the result at high stresses.

General model for testing solar domestic hot water systems

Abstract For modelling solar domestic hot water (SDHW) systems, a plug flow store model is presented. It is used in conjunction with the dynamic system testing algorithm to predict the long term performance of SDHW systems from short term test data. The basic property of a plug flow model is its capability of modelling drawoffs without any mixing inside the store. As an extension, the model developed in this paper covers the range between pure plug flow and full mixing. The degree of draw off mixing is characterized by a continuous parameter instead of a (discrete) number of thermal nodes which actually is defined neither for a plug flow model nor for a real system. Less than ten model parameters characterize a system under test. It was found that the parameters can be identified in short time (two to four weeks outdoors) for a large class of systems, e.g. thermosyphon systems or integrated collector store (ICS) systems, with load side heat exchanger, auxiliary heater, and heat pipe collectors. A summary of experimental results for different systems is given.

A method for comparing and combining short-term genotoxicity test data: The optimal use of dose information

A method for comparing and combining short-term genotoxicity test data: The optimal use of dose information

A method for combining and comparing short-term genotoxicity test data: Preface: A report from ICPEMC Committee 1

A method for combining and comparing short-term genotoxicity test data: Preface: A report from ICPEMC Committee 1