Recent Developments of Noise Attenuation Using Acoustic Barriers for a Specific Edge Geometry

The aim of this research is to provide a better prediction for noise attenuation using thin rigid barriers. In particular, the paper presents an analysis on four methods of computing the noise attenuation using acoustic barriers: Maekawa-Tatge formulation, Kurze and Anderson algorithm, Menounou formulation, and the general prediction method (GPM-ISO 9613). Accordingly, to improve the GPM, the prediction computation of noise attenuation was optimized for an acoustic barrier by considering new effects, such as attenuation due to geometrical divergence, ground absorption-reflections, and atmospheric absorption. The new method, modified GPM (MGPM), was tested for the optimization of an y-shape edge geometry of the noise barrier and a closed agreement with the experimental data was found in the published literature. The specific y-shape edge geometry of the noise barrier contributes to the attenuation due to the diffraction phenomena. This aspect is based on the Kirchhoff diffraction theory that contains the Huygens-Fresnel theory, which is applied to a semi-infinite acoustic barrier. The new method MGPM of predicting the noise attenuation using acoustic barriers takes into consideration the next phenomena: The effect of the relative position of the receiver, the effect of the proximity of the source or receiver to the midplane of the barrier, the effect of the proximity of the receiver to the shadow boundary, the effect of ground absorption-reflections, the effect of atmospheric absorption, and the meteorological effect due to downwind. The conclusion of the paper reveals the optimization of the method for computing the noise attenuation using acoustic barriers, including the necessary corrections for ISO-9613 and the Sound PLAN software, as well as the optimization on a case study of a specific geometry of the edge barrier.

Effect of cutting edge geometry change due to tool wear on hole quality in drilling of carbon fiber reinforced plastics using advanced ceramic coated tools

This paper aims to study the evolution of cutting edge geometry due to tool wear and discuss its impact on the hole quality of a carbon fiber reinforced plastic (CFRP) laminate. A drilling experiment was conducted using three types of twist drills: uncoated, BAM (AlMgB14) coated, and (AlCrSi/Ti)N nanocomposite coated tungsten carbide tools. After generating 120 holes, the uncoated drill had the largest cutting edge radius (∼36 µm), while the BAM coated drill had the most extensive flank wear (∼287 µm) among the three drills. This relatively rapid tool wear results in a reduction of average hole size and a considerable variation on the hole profiles. The worn drills with the cutting edge radius greater than 19.3 µm form the fiber pull-outs in not only the 135° plies but also the adjacent 45° and 90° plies from the cutting direction, creating deep void networks. This type of networked fiber pull-out damage was observed with the holes machined by the uncoated and BAM coated drills. The (AlCrSi/Ti)N coated drill, which experienced the least amount of flank wear and the least increase of cutting edge radius, generated consistently sized holes up to 120 holes. However, the relatively sharp (AlCrSi/Ti)N coated tool results in the higher arithmetic roughness average (Ra) and the maximum roughness height (Rz) values than the other tools due to the localized fiber pull-outs and the absence of severe matrix smearing.

THE EFFECT OF THE CIRCULAR FEED ON THE SURFACE ROUGHNESS AND THE MACHINING TIME

The surface roughness is analysed in different feeds and turning procedures (rotational and conventional) in this paper. Cutting experiments were made on different cutting speeds and feed rates with 2 cutting tool with helical edge geometry and 1 traditional turning tool. The measured 2D surface roughness values were compared between the different cutting tools. The benefit of the circular feed application is showed by the decrease of roughness parameters and machining time.

A MICROSTRUCTURE-BASED MECHANISTIC MODEL FOR BONE SAWING: PART 2 - ACOUSTIC ENERGY RATE PREDICTIONS

Part-2 of this paper is focused on modeling the acoustic emission (AE) energy rate as a function of the specific cortical bone microstructures (viz., osteon, interstitial matrix, lamellar bone, and woven bone) and the depth-of-cut encountered by the bone sawtooth. First, the AE signal characteristics from the sawing experiments (in Part-1) are related to the pure haversian and pure plexiform regions of the cut. Using the cutting force predictions from Part-1 as input, the AE energy rate is then modeled in terms of the energies dissipated in the shearing and ploughing zones encountered by the rounded cutting edge. For this calculation, the rounded edge geometry of the sawtooth is modeled as a combination of (i) shear-based cutting from a negative rake cutting tool; and (ii) ploughing deformation from a round-nose indenter. The spread seen in the AE energy rate is captured by modeling the variations in sawed surface height profile, tool cutting edge geometry, and porosity of the bone. The model calibration and validation protocols are similar to those used in Part-1. The validated AE model is useful for process planning both in terms of its ability to predict AE energy rate trends and cutting force variations, based on the differences in the underlying bone microstructures.

A Method for Simultaneous Optimization of Blank Shape and Forming Tool Geometry in Sheet Metal Forming Simulations

This paper presents a numerical method for simultaneous optimization of blank shape and forming tool geometry in three-dimensional sheet metal forming operations. The proposed iterative procedure enables the manufacturing of sheet metal products with geometry fitting within specific tolerances (surface and edge deviations less than 0.5 or 1.0 mm, respectively) that prescribe the maximum allowable deviation between the simulated and desired geometry. Moreover, the edge geometry of the product is affected by the shape of the blank and by an additional trimming phase after the forming process. The influences of sheet metal thinning, edge geometry, and springback after forming and trimming are considered throughout the blank and tool optimization process. It is demonstrated that the procedure effectively optimizes the tool and blank shape within seven iterations without unexpected convergence oscillations. Finally, the procedure thus developed is experimentally validated on an automobile product with elaborated design and geometry which prone to large springback amounts owning to complex-phase advanced high strength steel material selection.

Ultrashort-pulsed laser separation of glass-silicone-glass substrates: influence of material properties and laser parameters on dicing process and cutting edge geometry

In recent years, ultrashort-pulsed lasers have increased their applicability for industrial requirements, as reliable femtosecond and picosecond laser sources with high output power are available on the market. Compared to conventional laser sources, high quality processing of a large number of material classes with different mechanical and optical properties is possible. In the field of laser cutting, these properties enable the cutting of multilayer substrates with changing material properties. In this work, the femtosecond laser cutting of phosphor sheets is demonstrated. The substrate contains a 230 µm thick silicone layer filled with phosphor, which is embedded between two glass plates. Due to the softness and thermal sensitivity of the silicone layer in combination with the hard and brittle dielectric material, the separation of such a material combination is challenging for both mechanical separation processes and cutting with conventional laser sources. In our work, we show that the femtosecond laser is suitable to cut the substrate with a high cutting edge quality. In addition to the experimental results of the laser dicing process, we present a universal model that allows predicting the final cutting edge geometry of a multilayer substrate.