Monitoring the frictional behavior of rock discontinuities is essential for the identification of potential natural hazards caused by mechanical instability. Active seismic monitoring of changes in transmitted and/or reflected compressional (P) and shear (S) waves has been used as a non-destructive method to assess the degree of damage inside rock and to monitor slip along a discontinuity. The objective of this study is to explore the geophysical response of a saturated rock joint undergoing shear. Laboratory shear tests are conducted on prismatic Indiana limestone specimens. Induced tension fractures resulted in specimens composed of two blocks (152.4 mm 127.0 mm 50.8 mm) with rough contact surfaces. Direct shear experiments were performed inside a metal confinement chamber under an effective normal stress of 2 MPa on water-saturated specimens. During the experiments, the chamber pressure, the total normal load, the shear load and the slip displacement were monitored. During the tests, continuous pulses of P- and S-waves were transmitted through the specimen and the amplitudes of the transmitted and reflected waves were recorded. The paper provides results of the mechanical and geophysical response of saturated joints and compares them with those obtained from similar, but dry, joints. For dry joints, both transmitted and reflected P- and S-waves show a distinct peak wave amplitude prior to shear failure. However, for saturated joints, a distinct peak in amplitude is only observed in both transmitted and reflected S-waves. Transmitted and reflected P-waves, propagated through saturated rock, displayed a continuous decrease and increase in amplitude, respectively, but had a sudden change in the rate of amplitude change that can be taken as a seismic precursor to joint shear failure.
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This content will become publicly available on February 1, 2025
A comparison of damping-based methods to identify damage to carbon-fiber-reinforced polymers laminates subjected to low-velocity impact
A method for detecting low-velocity impact damage in carbon fiber reinforced polymer (CFRP) is presented. It involves the use of the Impulse Excitation Technique (IET) and hysteresis loops to calculate the damping parameter of T700/NCT304-1 carbon/epoxy samples subjected to various low-velocity impact energies. The value of the coefficient of restitution (COR) is determined for each impact, ranging between 0.62 for the lowest impact energy to 0.48 for the highest one. The results reveal that a three-step increase in the damping parameter exists in all cases as the impact energy on the specimen increases. An abrupt jump in the damping parameter value is observed for impact energies exceeding ∼0.9 of the material's maximum capacity. Overall, at the highest impact energy equal to 3.65 J, the damping parameter increased by 43.3% compared to the pristine specimen. Additionally, two cases of cyclic tension-tension loading were applied to the specimens, with maximum stresses set at 150 MPa and 200 MPa. The measured values of plastic and elastic strain energy were used to determine the damping ratios. For both cases, the damping of the specimen subjected to the highest impact energy was ∼1.2 times greater than that of an intact specimen, with an increase pattern similar to the findings of the IET method. Optical microscope images of the specimens are provided to illustrate various damage modes observed in the composite materials.
more » « less- Award ID(s):
- 1946231
- NSF-PAR ID:
- 10496331
- Publisher / Repository:
- https://journals.sagepub.com/doi/10.1177/00219983231225451
- Date Published:
- Journal Name:
- Journal of Composite Materials
- Volume:
- 58
- Issue:
- 3
- ISSN:
- 0021-9983
- Page Range / eLocation ID:
- 401 to 417
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Conclusion In vitro thin‐film mechanical analysis techniques can readily characterize the effects of SC's exposure to UV radiation. The methods used in this study demonstrated commercial sunscreens were able to preserve the biomechanical properties of SC during UV exposure, thus indicating the barrier function of SC was also maintained. -
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1. INTRODUCTION The fracturing in laboratory-scale rock specimens is often characterized by the deformation of the inelastic region surrounding the crack tips, also known as the fracture process zone (FPZ) (Backers et al., 2005; Ghamgosar and Erarslan, 2016). While the influence of the FPZ on mode I fracture in rocks has been extensively investigated, there are limited studies on FPZ development in rocks under pure mode II loading (Ji et al., 2016; Lin et al., 2020; Garg et al., 2021; Li et al., 2021).
