Triaxial Cyclic Compression Testing of hot mix asphalt with cyclic confining pressure

2014 ◽  
pp. 391-404 ◽  
Keyword(s):  
Hot Mix Asphalt ◽  
Confining Pressure ◽  
Compression Testing ◽  
Cyclic Compression

scholarly journals Factors influencing mechanical properties of polyurethane foams used in compressible flexographic sleeves

2020 ◽  
Author(s):  
Saša Petrović ◽  
◽  
Nemanja Kašiković ◽  
Željko Zeljković ◽  
Rastko Milošević ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Polyurethane Foams ◽  
Compression Testing ◽  
Foam Layer ◽  
Cyclic Compression ◽  
Factors Influencing ◽  
Pu Foam ◽  
Flexographic Printing ◽  
Creep And Stress Relaxation

Polyurethanes are a group of polymers which are in many ways different from other types of plastic. They are used in many different areas due to the fact that many different chemicals can be used during their synthesis, resulting in a variety of structures. Sleeves are comprised of hard base often covered with compressible polyurethane (PU) foam layer. PU foam layer can have different composition and level of porosity which are the main factors influencing compressibility of the sleeve and therefore its area of use. Sleeves are also one of the least researched components in the flexographic printing process. However, mechanical properties of the polyurethane, its fatigue, lifespan and parameters influencing all of them have been extensively investigated in different areas and for different types and formulations of polyurethane. The aim of this paper is to investigate factors influencing mechanical properties of polyurethane foams used in compressible flexographic sleeves. Investigated parameters are foam density, level of strain and strain rate, influence of microstructure under different conditions and parameters influencing creep and stress relaxation. The review of the existing literature regarding mechanical properties of the PU foams makes it possible to select the parameters with the greatest possible influence on the flexographic printing process, as well as to find the most suitable methods to investigate the effect of exploitation on sleeve properties. As a large number of parameters influencing PU foam mechanical properties are fixed during printing, it can be concluded, through the review of the existing literature, that the main parameters to be investigated are the resilience of the sleeve compressible layer during cyclic compression testing (residual strain), maximum stress, Young’s modulus, hysteresis loss, and creep and stress relaxation during cyclic compression testing with strain retention.

Effects of Testing Time and Confining Pressure on Falling-Head Permeability Tests of Hot-Mix Asphalt Concrete

2000 ◽  
Vol 1723 (1) ◽  
pp. 92-96 ◽  
Author(s):  
Kevin D. Hall ◽  
Josue Cruz ◽  
Hooi Ng
Keyword(s):  
Asphalt Concrete ◽  
Hot Mix Asphalt ◽  
Confining Pressure ◽  
Water Infiltration ◽  
Time Interval ◽  
Testing Time ◽  
Test Results ◽  
Testing Procedures ◽  
Superpave Gyratory Compactor ◽  
Flexible Wall

Superpave implementation has resulted in increased interest in the permeability of hot-mix asphalt concrete. Relatively open-graded Superpave mixes have given rise to concern about premature pavement failures due to increased water infiltration from the surface. Arkansas is investigating the use of a falling-head permeability test to evaluate Superpave mixes with respect to potential performance problems caused by increased permeability. The initial phase of the project concerns the development of laboratory testing procedures and equipment. Superpave field mixes from projects in Arkansas were sampled to investigate permeability testing parameters. In addition, compacted test specimens from a round-robin study of permeability were included in the testing matrix. For the Arkansas mixes, loose mix sampled at the hot-mix plant was compacted using the Superpave gyratory compactor. Field cores were also taken from completed pavement sections. Permeability tests were conducted on all samples to investigate the effect of testing time (15, 30, 45, and 60 min) and confining pressure (69 and 96.5 kPa) on the measured permeability values. Results of the testing suggest that neither the time interval used in measuring the head drop in a falling-head test nor the confining pressure used in the flexible wall testing apparatus significantly affects test results. These findings will greatly simplify testing methods and setup, making the test more attractive as a relatively routine tool for the mix design laboratory.

Precipitate coarsening during hot-compression testing of NiAl + 2 at.% Nb

1986 ◽  
Vol 44 ◽  
pp. 598-599
Author(s):  
W. M. Sherman ◽  
K. M. Vedula
Keyword(s):  
High Temperature ◽  
Flow Stress ◽  
Weight Ratio ◽  
Constant Strain Rate ◽  
Hot Compression ◽  
Compression Testing ◽  
Second Phase ◽  
Precipitate Coarsening ◽  
High Temperature Mechanical Properties ◽  
Ordered Intermetallic

The strength to weight ratio and oxidation resistance of NiAl make this ordered intermetallic, with some modifications, an attractive candidate to compete with many superalloys for high temperature applications. Recent studies have shown that the inherent brittleness of many polycrystalline intermetallics can be overcome by micro and macroalloying. It has also been found that the high temperature mechanical properties of NiAl can be enhanced through the addition of Nb by powder metallurgical techniques forming a dispersed second phase through interdiffusion in a polycrystalline matrix. A drop in the flow stress is observed however in a NiAl-2 at.% Nb alloy after 0.2 % strain during constant strain rate hot compression testing at 1025°C. The object of this investigation was to identify the second phase and to determine the cause of the flow stress drop.

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