Evaluation of a vertical-scale, fixed-index instrument display panel for the X-15 airplane

Analog simulation to compare pilot performance in using operational X-15 instrument panel, and vertical scale, fixed index instrument display pane

Fast Determination of Soil Behavior in the Capillary Zone Using Simple Laboratory Tests

INE/AUTC 13.1

Correlation of creep rate with microstructural changes during high temperature creep

Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten

Expansive Soil Pavement Design Using Case Studies

A study of the field behavior of airport pavements on expansive soils was made for the purpose of developing design procedures for expansive soil areas. Through theoretical developments, computer simulation and empirical calibration a pavement thickness design procedure was developed. The selection of pavement thickness using the method insures a stiff enough pavement to reduce differential movements to acceptable levels based on calculated aircraft response. Differential movements are calculated using a soil model developed from recent concepts of expansive soil behavior. A soil pavement interaction model was derived for calculating the restraint provided by pavement stiffness

Weak form equation–based finite-element modeling of viscoelastic asphalt mixtures

The objective of this study is to demonstrate using weak form partial differential equation (PDE) method for a finite-element (FE) modeling of a new constitutive relation without the need of user subroutine programming. The viscoelastic asphalt mixtures were modeled by the weak form PDE-based FE method as the examples in the paper. A solid-like generalized Maxwell model was used to represent the deforming mechanism of a viscoelastic material, the constitutive relations of which were derived and implemented in the weak form PDE module of Comsol Multiphysics, a commercial FE program. The weak form PDE modeling of viscoelasticity was verified by comparing Comsol and Abaqus simulations, which employed the same loading configurations and material property inputs in virtual laboratory test simulations. Both produced identical results in terms of axial and radial strain responses. The weak form PDE modeling of viscoelasticity was further validated by comparing the weak form PDE predictions with real laboratory test results of six types of asphalt mixtures with two air void contents and three aging periods. The viscoelastic material properties such as the coefficients of a Prony series model for the relaxation modulus were obtained by converting from the master curves of dynamic modulus and phase angle. Strain responses of compressive creep tests at three temperatures and cyclic load tests were predicted using the weak form PDE modeling and found to be comparable with the measurements of the real laboratory tests. It was demonstrated that the weak form PDE-based FE modeling can serve as an efficient method to implement new constitutive models and can free engineers from user subroutine programming

Implementation of pseudo J-integral based Paris’ law for fatigue cracking in asphalt mixtures and pavements

Pavement analysis and design for fatigue cracking involves a number of practical problems like material assessment/screening and performance prediction. A mechanics-aided method can answer these questions with satisfactory accuracy in a convenient way when it is appropriately implemented. This paper presents two techniques to implement the pseudo J-integral based Paris’ law to evaluate and predict fatigue cracking in asphalt mixtures and pavements. The first technique, quasi-elastic simulation, provides a rational and appropriate reference modulus for the pseudo analysis (i.e., viscoelastic to elastic conversion) by making use of the widely used material property: dynamic modulus. The physical significance of the quasi-elastic simulation is clarified. Introduction of this technique facilitates the implementation of the fracture mechanics models as well as continuum damage mechanics models to characterize fatigue cracking in asphalt pavements. The second technique about modeling fracture coefficients of the pseudo J-integral based Paris’ law simplifies the prediction of fatigue cracking without performing fatigue tests. The developed prediction models for the fracture coefficients rely on readily available mixture design properties that directly affect the fatigue performance, including the relaxation modulus, air void content, asphalt binder content, and aggregate gradation. Sufficient data are collected to develop such prediction models and the R2 values are around 0.9. The presented case studies serve as examples to illustrate how the pseudo J-integral based Paris’ law predicts fatigue resistance of asphalt mixtures and assesses fatigue performance of asphalt pavements. Future applications include the estimation of fatigue life of asphalt mixtures/pavements through a distinct criterion that defines fatigue failure by its physical significance

Modelling cracking damage of asphalt mixtures under compressive monotonic and repeated loads using pseudo J-integral Paris’ law

Field observations and mechanical analyses have shown that cracks accompany rutting in asphalt mixtures under external compressive loads. This study aims to model crack growth in asphalt mixtures under compressive monotonic and repeated loads. Using energy equilibrium and viscoelastic Griffith fracture criterion, a damage density characterising the cracks in mixtures is derived as a function of stress, nonlinear viscofracture strain, asphalt film thickness and bond energy. Crack evolution is modelled by pseudo J-integral Paris’ law. Six types of asphalt mixture were tested by monotonic compressive strength tests at 40°C. Two were further tested at four more temperatures and four more loading rates, respectively. Repeated load test results for the same mixtures were obtained from previous studies. The different shape of the damage density curve (S-shape for monotonic load and increasing exponential shape for repeated load) demonstrates the dependence of damage growth on loading mode, due to different energy release rates. Pseudo J-integral Paris’ law can model the crack growth in mixtures and capture the post-peak softening behaviour under a monotonic load. The Paris’ law coefficients (A and n) are independent of loading mode (monotonic or repeated), rate or temperature. They are fundamental material properties and can be used to predict crack growth under varying loading and temperature conditions

South Korea´s expanding regional and global roles: challenges and perspectives

In the last four decades the Republic of Korea (South Korea or Korea) developed from a poor country and an agrarian society into a wealthy and industrial nation and a world leader in important areas such as information technology and innovation. Despite its remarkable achievements at the national level, at the regional and global levels Korea´s role was somewhat marginal until the 1990s. With the end of the Cold War and its diplomatic foundations established Korea´s foreign policy underwent rapid transformations; its scope became global and included what has been called “summit diplomacy”, designed to consolidate friendly relations and start new partnerships and projects of cooperation for the 21th century. At the regional level it is an active member of Asean+3, of Apec and of other organizations; since 2008 it maintains annual Trilateral Summit Meetings with China and Japan, and in September 2011 Seoul became seat of the Trilateral Cooperation Secretariat. Only a few years after joining the UN (1991), in November 1995 the country was elected a non-permanent member of the UNSC, and recently was again elected for the period of 2013-2014; in 2006 Ban Ki-moon,a Korean Diplomat, was elected the 8th Secretary General of the UN and in June 2011 he had his mandate renewed until 2016. These and other important achievementsare evidence of Korea´s assertive role as a regional and global actor. To strengthen cooperation with established and emerging international partners the country will rely on the following policy directions and strategies: expand export markets, attract FDI, pursue bilateral trade and intensify ties with major trading partners. It is clear, however, that in addition to its undeniable economic success story and political achievements at the regional and international levels, external variables are quite important in Korea´s determination to expand its regional and global roles: the domestic and international policies and consequent strategies implemented by China, the United States, and Japan, as well the future relationships among these three countries. The relationships between the US and China, in particular, will determine to a large extent what will happen in East Asia. China has become Korea´s number one trade partner, but Korea is heavily dependent on the US for security and military assistance. Therefore, the new Korean government is expected to play a kind of pendulum strategy between the two major powers, as well as a somewhat neutral role with respect to Sino-Japanese China relations.Nas últimas quatro décadas, a República da Coreia (Coreia do Sul ou Coreia) transformou-se de um país pobre, com uma sociedade agrária dilacerada pela guerra, em uma nação industrial e moderna, líder em importantes áreas, como tecnologia da informação e inovação. Apesar do notável desempenho nacional, o papel da Coreia como ator regional e global era considerado pouco expressivo até os anos 1990. Com o fim da Guerra Fria e a consolidação de suas bases diplomáticas, a política externa da Coreia passou por rápidas transformações; seu escopo tornou-se global e incluiu o que tem sido chamado “diplomacia de cúpula”, com o objetivo de fortalecer as relações já existentes e iniciar novas parcerias e projetos de cooperação para o século XXI. Em nível regional, a Coreia tornou-se membro ativo da Asean+3, da Apec e de outras organizações; desde 2008 mantém cúpulas trilaterais anuais com a China e com o Japão, e em setembro de 2011 Seul tornouse sede do Secretariado para a Cooperação Trilateral. Poucos anos após ingressar na ONU (1991), em novembro de 1995 o país foi eleito membro não permanente do Conselho de Segurança e recentemente foi novamente eleito para o período de 2013-2014; em 2006 o diplomata coreano Ban Ki-moon foi eleito o 8o secretáriogeral da ONU, e em junho de 2011 teve seu mandato renovado até 2016. Estas e outras importantes conquistas evidenciam o papel assertivo da Coreia como ator regional e global. A fim de fortalecer a cooperação com parceiros já estabelecidos e com países emergentes, a Coreia propõe as seguintes políticas e estratégias: expansão do mercado exportador, atração de IED, consolidação do comércio bilateral e intensificação dos laços com os principais parceiros.  Entretanto, além de seu inegável sucesso econômico e conquistas políticas nos panoramas regional e global, variáveis externas desempenham importante papel na determinação da Coreia de ampliar seu papel de ator regional e global: as políticas domésticas e internacionais e as consequentes estratégias a serem desenvolvidas pela China, pelos EUA e pelo Japão, bem como as relações futuras entre esses três países. As relações entre os EUA e a China, em particular, irão determinar futuros acontecimentos no Leste Asiático. A China é hoje o maior parceiro comercial da Coreia, mas este país depende dos EUA para sua segurança e apoio militar. Portanto, espera-se que o novo governo coreano mantenha uma estratégia de pêndulo em suas relações com a China e com os EUA e, ao mesmo tempo, neutralidade no que se refere às relações entre Japão e China

Structural Characteristics of Unbound Aggregate Bases to Meet AASHTO 2002 Design Requirements: Interim Report

This report gives the results of a study of the properties of unbound aggregate base materials using both laboratory testing data from full scale field tests in Illinois, Georgia, and Texas, and a model of cross-anisotropic elastic materials to characterize the behavior of the base materials under traffic loads. Using the cross-anisotropic model, the stress distribution in a base course is more realistic than that developed when the aggregate base is considered to be linear and isotropic. The stress distribution based on cross-anisotropic analysis is not only more correct, but it is also more favorable to the unbound aggregate in that significant tensile stresses are found not to occur. The analogy is presented in this report that the response of the aggregate base to the load is as if the stress distribution directly under the wheel load due to anisotropy acts as a moving column under the wheel in which the aggregate essentially produces its own confinement and does not enter into tension. Other findings in this report include the following: 1) The unbound aggregate base material should be modeled as non-linear and cross-anisotropic to account for stress-sensitivity and the significant differences between vertical and horizontal moduli and Poisson’s ratios. 2) The ICAR laboratory testing protocol is efficient and precise and should be considered as a candidate to model the unbound aggregate base. The protocol uses three stress regimes and ten stress levels within each regime to determine stress sensitivity and cross-anisotropy. A system identification method is used to select the five material properties based on the tests results necessary to properly characterize the aggregate base and to satisfy the requirements of elastic work potential theory. 3) The Fast Industrial Process Controls cell is efficient and should be used to characterize unbound aggregate bases. The ratio of the diameter to the specimen height is 1:1. While testing of such sample sizes is discouraged in the literature, improvements made to the IPC cell minimize frictional development between the sample and loading platens resulting in minimal constraint at the sample ends. This is verified in the report based on comparative triaxial testing and finite element analysis. 4) The ICAR testing protocol is an excellent tool for both unbound aggregate characterization and comparative analysis of materials. A compaction study on two very different aggregates (uncrushed river gravel and crushed limestone) was performed in which the aggregates were subjected to impact, kneading gyratory compaction. The difference in the tendency of the compaction techniques to produce varying levels of particle orientation (which affects anisotropy) was evident in the degree of anisotropy measured.Aggregates Foundation for Technology, Research, and Education (AFTRE)Civil, Architectural, and Environmental Engineerin