Systems and methods for determining whether mechanical fatigue exists in a downhole cable using thermally-induced acoustic waves are disclosed herein. A cable fatigue monitoring system includes a thermal source, one or more light sources, one or more photodetector arrays, and a computing system comprising a processor, a memory, and a cable distortion module. The cable distortion module is operable to generate acoustic waves in a cable using the thermal source, direct light from the one or more light sources toward the cable, detect light from the one or more light sources transmitted past the cable at the one or more photodetector arrays, and determine, based on the detected light transmitted past the cable, whether a change in velocity of the acoustic waves has occurred in the cable.

A dynamic friction experimental device includes a base, an incident bar, an axial compression device, and a torque loading device. The base is provided with a displacement-constrain structure, and the incident bar includes a first incident section and a second incident section. The first incident section is arranged adjacent to the displacement-constrain structure, and the second incident section is connected to the first incident section. At a joint of the first incident section and the second incident section, a projection of a cross section of the first incident section is positioned in a cross section of the second incident section along an axial direction of the second incident section. When the dynamic mechanical property of a specimen is tested, the axial compression device is configured to apply pressure to the second incident section, and the torque loading device is configured to apply torque to the second incident section.

A racquet extending along a longitudinal axis and including a frame including a head portion, a handle portion, and a throat portion. The head portion forms a hoop that defines a string bed plane. At least the head portion and the throat portion of the frame are formed at least in part of a fiber composite material. When the racquet is tested under the racquet lateral bending test, the racquet has a lateral deflection of at least 6.0 mm when measured in a direction that is parallel to the string bed plane and perpendicular to the longitudinal axis. When the racquet is tested under the racquet torsional stability test, the racquet has an angular deflection of less than 5.5 degrees about the longitudinal axis. The head portion has a maximum beam height distance of at least 20 mm.

A racquet extending along a longitudinal axis and including a frame including a head portion, a handle portion, and a throat portion. The head portion forms a hoop that defines a string bed plane. At least the head portion and the throat portion of the frame are formed at least in part of a fiber composite material. When the racquet is tested under the racquet lateral bending test, the racquet has a lateral deflection of at least 6.0 mm when measured in a direction that is parallel to the string bed plane and perpendicular to the longitudinal axis. When the racquet is tested under the racquet torsional stability test, the racquet has an angular deflection of less than 5.5 degrees about the longitudinal axis. The head portion has a maximum beam height distance of at least 20 mm.