A Novel Test Specimen Geometry for Uniaxial Fatigue Testing of Asphalt Concrete

2019 ◽  
Vol 47 (5) ◽  
pp. 20180564
Author(s):  
Grant J. Karr ◽  
Adrian R. Archilla
Keyword(s):  
Asphalt Concrete ◽  
Test Specimen ◽  
Fatigue Testing ◽  
Specimen Geometry

scholarly journals An Overview of Fatigue Testing Systems for Metals under Uniaxial and Multiaxial Random Loadings

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 447
Author(s):  
Julian M. E. Marques ◽  
Denis Benasciutti ◽  
Adam Niesłony ◽  
Janko Slavič
Keyword(s):  
Fatigue Testing ◽  
Local State ◽  
Specimen Geometry ◽  
Present Review ◽  
General Criterion ◽  
Classification Criterion ◽  
Test Type ◽  
State Of Stress ◽  
The Relationship

This paper presents an overview of fatigue testing systems in high-cycle regime for metals subjected to uniaxial and multiaxial random loadings. The different testing systems are critically discussed, highlighting advantages and possible limitations. By identifying relevant features, the testing systems are classified in terms of type of machine (servo-hydraulic or shaker tables), specimen geometry and applied constraints, number of load or acceleration inputs needed to perform the test, type of loading acting on the specimen and resulting state of stress. Specimens with plate, cylindrical and more elaborated geometry are also considered as a further classification criterion. This review also discusses the relationship between the applied input and the resulting local state of stress in the specimen. Since a general criterion to classify fatigue testing systems for random loadings seems not to exist, the present review—by emphasizing analogies and differences among various layouts—may provide the reader with a guideline to classify future equipment.

Specimen Geometry Study for Direct Tension Test Based on Mechanical Tests and Air Void Variation in Asphalt Concrete Specimens Compacted by Superpave Gyratory Compactor

2000 ◽  
Vol 1723 (1) ◽  
pp. 125-132 ◽  
Author(s):  
Ghassan R. Chehab ◽  
Emily O’Quinn ◽  
Y. Richard Kim
Keyword(s):  
Asphalt Concrete ◽  
Tensile Testing ◽  
Complex Modulus ◽  
Specimen Geometry ◽  
Uniaxial Tensile ◽  
Void Content ◽  
Uniaxial Tensile Testing ◽  
Superpave Gyratory Compactor ◽  
Air Void ◽  
Air Void Content

Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave gyratory compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries—75 × 115, 75 × 150, 100 × 150, and 100 × 200 mm—to study the effect of geometry boundary conditions on responses. On the basis of graphical and statistical analysis, it was determined that there was an effect on the dynamic modulus at certain frequencies but no effect on the phase angle. Except for 75 × 115 mm, all geometries behaved similarly under the monotonic test. From these findings and other considerations, it is recommended that the 75- × 150-mm geometry, which is more conservative, and the 100- × 150-mm geometry be used for tensile testing.

Adjusted J-R Toughness Curve for Pipes Using J-A2 Crack Constraint of CT Specimens and 3D Crack Meshes

2019 ◽  
Author(s):  
Greg Thorwald ◽  
Ken Bagnoli
Keyword(s):  
Fracture Mechanics ◽  
Test Data ◽  
Crack Front ◽  
Test Specimen ◽  
Closed Form Solution ◽  
Form Solution ◽  
Specimen Geometry ◽  
Ductile Tearing ◽  
Two Parameter ◽  
Axial Surface

Abstract The objective of this paper is to use two-parameter fracture mechanics to adjust a material J-R resistance curve (i.e. toughness) from the test specimen geometry to the cracked component geometry. As most plant equipment is designed and operated on the “upper shelf”, a ductile tearing analysis may give a more realistic assessment of flaw tolerance. In most cases, tearing curves are derived from specimen geometries that ensure a high degree of constraint, e.g., SENB and CT Therefore, there can be significant benefit in accounting for constraint differences between the specimen geometry and the component geometry. In one-parameter fracture mechanics a single parameter, K or J-integral, is sufficient to characterize the crack front stresses. When geometry dependent effects are observed, two-parameter fracture mechanics can be used to improve the characterization of the crack front stress, using T-stress, Q, or A2 constraint parameter. The A2 parameter was be used in this study. The usual J-R power-law equation has two coefficients to curve-fit the material data (ASTM E1820). The adjusted J-R curve coefficients are modified to be a function of the A2 constraint parameter. The measured J-R values and computed A2 constraint values are related by plotting the J-R test data versus the A2 values. The A2 constraint values are computed by comparing the HRR stress solution to the crack front stress results of the test specimen geometry using elastic-plastic FEA. Solving for the two J-R curve coefficients uses J values at two Δa crack extension values from the test data. A closed-form solution for the adjusted J-R coefficients uses the properties of natural logarithms. The solution shows the adjusted J-R exponent coefficient will be a constant value for a particular material and test specimen geometry, which simplifies the application of the adjusted J-R curve. A different test specimen geometry can be used to validate the adjusted J-R curve. Choosing another test specimen geometry, having a different A2 constraint value, can be used to obtain the adjusted J-R curve and compare it to the measured J-R curves. The geometry of the component is also expected to have a different A2 constraint compared to the material test specimen. The example examined here is an axial surface flaw in a pipe. The A2 constraint for an axial surface cracked pipe is computed and used to obtain an adjusted J-R curve. The adjusted J-R curve shows an increase in toughness for the pipe as compared to the CT measured value. The adjusted J-R curve can be used to assess flaw stability using the driving force method or a ductile tearing instability analysis.

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