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831.
Along with alumium, titanium and composite alloys, magnesium alloys have been given much attention by industry for applications
such as lightweight automobiles and electronics because of their high strength, low specific density and good damping characteristics.
In this paper, creep tests were done with magnesium alloys (Mg-3% Zn-1% Mn, Mg-1.2% Zn-1% Mn, and Mg-3% Zn-1% Mn-0.3% Ca)
containing different amounts of Zn to investigate the effect of Zn and Ca on the deformation behavior and the rupture time
for Mg alloy creep under elevated temperatures. The alloys were obtained as follows: (1) pure magnesium (9.7 kg) was melted
at 720°C in an SF6 atmosphere; (2) the temperature was increased up to 800–820°C after adding 0.3 kg of pure Mn to make the
Mg-1% Mn master alloy; (3) the minor element (Zn, Ca) was added to the master alloy; and (4) the magnesium alloy melts were
cast into a metallic mold preheated to 150°C. The creep tests were executed under a constant load and temperature to measure
the steady-state rate and rupture time of creep. Based on the experimental results, the creep behavior of the alloys seemed
to be controlled by dislocation climb at around 0.5∼0.55Tm (Tm; melting temperature). In addition, the results showed that the addition of Ca was effective for increasing the creep resistance
of a Mg alloy: the more Zn present in the alloy, the stronger the creep strength of the alloy. 相似文献
832.
S. -S. Cho C. S. Shin C. S. Lee H. Chang K. W. Lee 《International Journal of Automotive Technology》2010,11(1):75-80
An engine cylinder head-block joint is a gasketed, bolted joint. Assessment of sealing performance and fatigue durability
of the joint during engine development relies entirely on the engine dynamometer test because the rig test cannot mimic the
engine run condition and finite element analysis employs gasket and bolt models that are too simple to provide the stress
data for fatigue assessment. This paper introduces finite element-based assessment of the gasket and the bolt and a model
that improves the analysis accuracy without increasing computation time. Experimental data for the deformation of joint members
under thermo-mehanical load are presented to demonstrate the accuracy of the model. 相似文献
833.
M. Demić D. Diligenski M. Demić I. Demić 《International Journal of Automotive Technology》2010,11(6):801-808
Macro and micro road profiles are of significant importance for vehicular motion studies, reliable calculations of vehicle
system properties, and ensuring vehicular safety. As such, road profiles should be considered carefully. Macro profiles consider
the spatial geometry of the road (curves, longitudinal and lateral slopes) while micro profiles consider roughness in longitudinal
and lateral directions. These profiles have random characteristics that can be quantified under onroad and off-road conditions
using a road profiler. This paper presents an analysis of a new concept for a universal profiler without gyroscopic stabilizers. 相似文献
834.
Rollover mitigation for a heavy commercial vehicle 总被引:1,自引:0,他引:1
Y. I. Ryu D. O. Kang S. J. Heo J. H. In 《International Journal of Automotive Technology》2010,11(2):283-287
A heavy commercial vehicle has a high probability of rollover because it is usually loaded heavily and thus has a high center
of gravity. An anti-roll bar is efficient for rollover mitigation, but it can cause poor ride comfort when the roll stiffness
is excessively high. Therefore, active roll control (ARC) systems have been developed to optimally control the roll state
of a vehicle while maintaining ride comfort. Previously developed ARC systems have some disadvantages, such as cost, complexity,
power consumption, and weight. In this study, an ARC-based rear air suspension for a heavy commercial vehicle, which does
not require additional power for control, was designed and manufactured. The rollover index-based vehicle rollover mitigation
control scheme was used for the ARC system. Multi-body dynamic models of the suspension subsystem and the full vehicle were
used to design the rear air suspension and the ARC system. The reference rollover index was tuned through lab tests. Field
tests, such as steady state cornering tests and step steer tests, demonstrated that the roll response characteristics in the
steady state and transient state were improved. 相似文献
835.
The dynamic stability of a vehicle depends on various maneuvering features, such as traction, braking, and cornering. This
study presents nonlinear vehicle models for estimating the stability region and simulating the dynamic behavior of a vehicle.
Two types of vehicle models were found by considering the degrees of freedom and linearity. A simple model with nonlinear
tire dynamics is useful for determining the stability region, while a complex model (a multi-body dynamic model in MSC.ADAMS)
is appropriate for carrying out accurate simulations. Actual data for a mid-sized passenger car were used, and the models
were validated by comparison with test results. 相似文献
836.
The behavior of a ship in regular waves during maneuvering was studied by using a two-time scale model. The maneuvering analysis was based on Söding’s (Schiffstechnik 1982; 29:3–29) nonlinear slender-body theory generalized to account for heel. Forces and moments due to rudder, propeller, and viscous cross-flow follow from the state-of-the-art procedures. The developed unified theory of seakeeping and maneuvering was verified and validated for calm water by comparing it with experimental and calculated zigzag and circle maneuvers. Linear wave-induced motions and loads were determined by generalizing the Salvesen-Tuck-Faltinsen (Trans SNAME 1970; 78:250–287) strip theory. The mean second-order wave loads in incident regular deep water waves in oblique sea conditions were estimated by the potential flow theories of Faltinsen et al. (Proc 13th Symp Naval Hydrody 1980), Salvesen (Proc Intl Symp Dynam Mar Vehicl Struct Wave 1974), and Loukakis and Sclavounos (J Ship Res 1978; 22:1–19). The considered theories cover the whole range of important wavelengths. Comparisons between the different mean second-order wave load theories and available experimental data were carried out for different ship hull forms when the ship was advancing forward on a straight course. The mentioned methods have been incorporated into the maneuvering model. Their applicability from the perspective of the maneuvering ability of the selected types of ships was investigated in given wave environments. The wave conditions are valid for realistic maneuvering cases in open coastal areas. It was demonstrated that the incident waves may have an important influence on the maneuvering behavior of a ship. The added resistance, mean second-order transverse force, and yaw moment also play important roles. 相似文献
837.
Ultimate collapse tests of stiffened-plate ship structural units 总被引:2,自引:0,他引:2
An increasingly popular approximate method for assessing ship hull girder ultimate strength is to combine the individual elasto-plastic load-carrying characteristics of each single stiffened-plate unit comprising the ship hull cross section. In order to evaluate methods (numerical and experimental) for developing the load-carrying characteristics (load–shortening curves), a full-scale testing system was designed and constructed to provide data for stiffened steel plate units under combined axial and lateral loads. The system included an assembly of discrete plate edge restraints that were developed to represent symmetric boundary conditions within a grillage system. Twelve full-scale panels including ‘as-built’, ‘deformed’ and ‘damaged’ specimens were tested in this set-up.
The specimens failed by combined plate and flexural buckling, stiffener tripping or local collapse, depending on the magnitude of lateral loads and local damage. Load-shortening curves associated with different failure modes were found to be distinctly different and it was found that a small lateral load could change the failure mode from flexural buckling to tripping. Current design criteria should directly consider effects of the lateral loads on the failure modes and the collapse loads of stiffened plates. 相似文献
838.
This paper proposes an elastic demand network equilibrium model for networks with transit and walking modes. In Hong Kong, the multi‐mode transit system services over 90% of the total journeys and the demand on it is continuously increasing. Transit and walking modes are related to each other as transit passengers have to walk to and from transit stops. In this paper, the multi‐mode elastic‐demand network equilibrium problem is formulated as a variational inequality problem where the combined mode and route choices are modeled in a hierarchical logit structures and the total travel demand for each origin‐destination pair is explicitly given by an elastic demand function. In addition, the capacity constraint for transit vehicles and the effects of bi‐directional flows on walkways are considered in the proposed model. All these congestion effects are taken into account for modeling the travel choices. A solution algorithm is developed to solve the multi‐mode elastic‐demand network equilibrium model. It is based on a Block Gauss‐Seidel decomposition approach coupled with the method of successive averages. A numerical example is used to illustrate the application of the proposed model and solution algorithm. 相似文献
839.
840.
Travel behavior researchers have been intrigued by the amount of time that people allocate to travel in a day, i.e., the daily
travel time expenditure, commonly referred to as a “travel time budget”. Explorations into the notion of a travel time budget
have once again resurfaced in the context of activity-based and time use research in travel behavior modeling. This paper
revisits the issue by developing the notion of a travel time frontier (TTF) that is distinct from the actual travel time expenditure
or budget of an individual. The TTF is defined in this paper as an intrinsic maximum amount of time that people are willing
to allocate for travel. It is treated as an unobserved frontier that influences the actual travel time expenditure measured
in travel surveys. Using travel survey datasets from around the world (i.e., US, Switzerland and India), this paper sheds
new light on daily travel time expenditures by modeling the unobserved TTF and comparing these frontiers across international
contexts. The stochastic frontier modeling methodology is employed to model the unobserved TTF as a production frontier. Separate
models are estimated for commuter and non-commuter samples to recognize the differing constraints between these market segments.
Comparisons across the international contexts show considerable differences in average unobserved TTF values. 相似文献