Experimental study on mode-I and mixed-mode crack propagation under tangentially incident P waves, S waves and reflected waves in blasts

Mixed-mode fracture of construction building materials under impact loading is quite common in civil engineering. The investigation of mixed-mode crack propagation behavior is an essential work for fundamental research and engineering application. A variable angle single cleavage semi-circle (VASCSC) specimen was proposed with which the dynamic fracture test was conducted by using a Split-Hopkinson pressure bar (SHPB). Notably, the mixed-mode crack propagation velocity could be detected by the synchronized crack velocity measuring system. With experimental results, the dynamic initiation stress intensity factors KI and KII were calculated by the experimental-numerical method. Additionally, the crack path of mixed-mode I/II fracture can be predicated precisely by using numerical method. Thus, a comprehensive approach of investigation on mixed-mode I/II fracture under impact loading was illustrated in this paper. The study demonstrates that the mixed-mode I/II crack would transform from complicated mode I/II to pure mode I during crack propagation, and several velocity decelerations induced crack deflection. The dynamic initiation fracture toughness of mixed-mode crack was determined by the experimental-numerical method. The VASCSC specimen has a great potential in investigating mixed-mode fracture problems with the SHPB device.

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Pre-Strain Effects on Mixed-Mode Fatigue Crack Propagation Behaviour of the P355NL1 Pressure Vessels Steel

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2018-85089 ◽

2018 ◽

Cited By ~ 2

Author(s):

João Ferreira ◽

José A. F. O. Correia ◽

Grzegorz Lesiuk ◽

Sergio Blasón González ◽

Maria Cristina R. Gonzalez ◽

...

Keyword(s):

Plastic Deformation ◽

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Propagation ◽

Crack Growth ◽

Fatigue Crack Propagation ◽

Mixed Mode ◽

Pressure Vessels ◽

Mode I ◽

Pure Mode

Pressure vessels and piping are commonly subjected to plastic deformation during manufacturing or installation. This pre-deformation history, usually called pre-strain, may have a significant influence on the resistance against fatigue crack growth of the material. Several studies have been performed to investigate the pre-strain effects on the pure mode I fatigue crack propagation, but less on mixed-mode (I+II) fatigue crack propagation conditions. The present study aims at investigating the effect of tensile plastic pre-strain on fatigue crack growth behavior (da/dN vs. ΔK) of the P355NL1 pressure vessel steel. For that purpose, fatigue crack propagation tests were conducted on specimens with two distinct degrees of pre-strain: 0% and 6%, under mixed mode (I+II) conditions using CTS specimens. Moreover, for comparison purposes, CT specimens were tested under pure mode I conditions for pre-strains of 0% and 3%. Contrary to the majority of previous studies, that applied plastic deformation directly on the machined specimen, in this work the pre-straining operation was carried out prior to the machining of the specimens with the objective to minimize residual stress effects and distortions. Results revealed that, for the P355NL1 steel, the tensile pre-strain increased fatigue crack initiation angle and reduced fatigue crack growth rates in the Paris region for mixed mode conditions. The pre-straining procedure had a clear impact on the Paris law constants, increasing the coefficient and decreasing the exponent. In the low ΔK region, results indicate that pre-strain causes a decrease in ΔKth.

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