A racquet includes a handle; and a frame connected to an end of the handle, the frame defining a rounded interior space, the frame including a negative Poisson's ratio (NPR) foam material, in which the NPR foam material, and in which the frame has a Poisson's ratio of between 0 and −1; and a network of strings stretched across the rounded interior space defined by the frame. A golf tee includes an elongated stem; and a head disposed at an end of the elongated stem and shaped to receive a golf ball; in which at least a portion of the golf tee is formed of a negative Poisson's ratio (NPR) foam material, in which the portion of the golf tee has a Poisson's ratio of between 0 and −1, and in which the NPR foam material includes an NPR metal foam, an NPR ceramic foam, or an NPR-PPR composite foam.

Ground surface comprising a substrate (110) having a Young's modulus of between 100 and 1000 GPa, and in which the ground surface has, on a working surface (120), a Vickers hardness of between 1300 and 10 000 kgf/mm.sup.2, and/or a surface coating forming the working surface, in which the surface coating contains amorphous carbon and/or titanium nitride and/or chromium nitride and/or tungsten carbide.

Ground surface comprising a substrate (110) having a Young's modulus of between 100 and 1000 GPa, and in which the ground surface has, on a working surface (120), a Vickers hardness of between 1300 and 10 000 kgf/mm.sup.2, and/or a surface coating forming the working surface, in which the surface coating contains amorphous carbon and/or titanium nitride and/or chromium nitride and/or tungsten carbide.

A flow meter includes a pair of ultrasonic transducers. Each transducer includes a housing, a piezoelectric crystal disposed within the housing, and a mini-horn array coupled to the housing. The mini-horn array, which may be formed via a 3D printing technique, includes an opening-free enclosure, a closed cavity inside the enclosure, and a plurality of horns enclosed within the closed cavity. The horns include a horn base portion adjacent to a proximal end surface of the cavity and a horn neck portion that extends from the base portion in a direction away from the piezoelectric crystal and towards a distal end surface of the cavity. The horn neck portions are separated by spaces within the cavity, wherein the spaces between the horn necks may be filled with powder.

A three-dimensional shaped article producing composition is provided and contains a plurality of particles, a solvent for dispersing the particles, and a binder having a function to temporarily bind the particles to one another in a state where the solvent is removed, wherein a volume-based average particle diameter of the particles is 0.1 μm or more and less than 50 μm, and a content ratio of the binder is 1.5 vol % or more and 10 vol % or less.

A sonotrode includes multiple layers of a material melted to one another to form a structure. The structure provides a base that has an attachment feature that is configured to operatively secure to an ultrasonic converter. The structure includes a shaft that extends from the base to a terminal end that provides a working surface that is configured to selectively engage a workpiece. The structure has at least one shaft that includes a first shaft that extends from the base to a first terminal end that provides a first working surface that is configured to selectively engage a workpiece. The first shaft is integrally formed with the base from the multiple layers to provide an unbroken, monolithic construction.

A method for preparing the prefabricated crack defects includes defining a defect area, defining a volume percentage of the crack defects in the defect area, adjusting the proportion of spherical powder, the proportion of hollow powder and process parameters of defect preparation according to the volume percentage of the crack defects, based on the technique of laser melting deposition, printing the defect area layer by layer by using the defect preparation powder and the process parameters of defect preparation, wherein the particle size of the defect preparation powder is between 45 μm and 150 μm, the proportion of spherical powder≥93% and the proportion of hollow powder<0.5%, the process parameters of defect preparation including: laser power of 450W-550W, scanning rate of 600 mm/min-1200 mm/min, powder feeding rate of 4 g/min-12 g/min, spot diameter of 1 mm-1.2 mm, scanning spacing of 0.5 mm-0.8 mm and layer thickness of 0.08 mm-0.2 mm.

A method for preparing the prefabricated crack defects includes defining a defect area, defining a volume percentage of the crack defects in the defect area, adjusting the proportion of spherical powder, the proportion of hollow powder and process parameters of defect preparation according to the volume percentage of the crack defects, based on the technique of laser melting deposition, printing the defect area layer by layer by using the defect preparation powder and the process parameters of defect preparation, wherein the particle size of the defect preparation powder is between 45 μm and 150 μm, the proportion of spherical powder≥93% and the proportion of hollow powder<0.5%, the process parameters of defect preparation including: laser power of 450W-550W, scanning rate of 600 mm/min-1200 mm/min, powder feeding rate of 4 g/min-12 g/min, spot diameter of 1 mm-1.2 mm, scanning spacing of 0.5 mm-0.8 mm and layer thickness of 0.08 mm-0.2 mm.

A method for preparing prefabricated gas pore defects includes: defining a defect area, defining a volume percentage of the gas pore defects in the defect area, adjusting the proportion of satellite powder, the proportion of hollow powder and the process parameters of defect preparation according to the volume percentage of the gas pore defects, based on the technique of laser melting deposition, printing the defect area layer by layer by using the defect preparation powder and the process parameters of defect preparation, wherein the particle size of the defect preparation powder is between 45 μm and 106 μm, the proportion of satellite powder is 55-65% and the proportion of hollow powder is 2.9-3.1%, the process parameters of defect preparation comprises: laser power of 600W-1000W, scanning rate of 400 mm/min-800 mm/min, powder feeding rate of 12 g/min-20 g/min, spot diameter of 1 mm-2 mm, scanning spacing of 0.5 mm-1 mm and layer thickness of 0.15 mm-0.2 mm.

A method for preparing prefabricated gas pore defects includes: defining a defect area, defining a volume percentage of the gas pore defects in the defect area, adjusting the proportion of satellite powder, the proportion of hollow powder and the process parameters of defect preparation according to the volume percentage of the gas pore defects, based on the technique of laser melting deposition, printing the defect area layer by layer by using the defect preparation powder and the process parameters of defect preparation, wherein the particle size of the defect preparation powder is between 45 μm and 106 μm, the proportion of satellite powder is 55-65% and the proportion of hollow powder is 2.9-3.1%, the process parameters of defect preparation comprises: laser power of 600W-1000W, scanning rate of 400 mm/min-800 mm/min, powder feeding rate of 12 g/min-20 g/min, spot diameter of 1 mm-2 mm, scanning spacing of 0.5 mm-1 mm and layer thickness of 0.15 mm-0.2 mm.