Experimental Techniques最新文献

Measuring dynamic forces acting on a structure over an extended bandwidth is difficult because of the influence of system dynamics. Such is the case for the measurement of the unsteady lift exerted on a flat-plate airfoil, the forces on which scale according to fluid dynamics scaling laws. To correct unsteady lift measurements for a flat-plate airfoil over a wider bandwidth, we present a force reconstruction technique using non-dimensional scaling laws as optimization criteria. In this non-dimensional scaling law, the amplitude and frequency of the power spectral densities (PSDs) of the total force measured over a range of flow speed conditions scale such that they collapse to a single curve. Two sets of optimization criteria, namely, minimizing the variance between the collapsed forces and curve-fitting a functional form for the force, are established to estimate modal participation factors for a specified number of resonance modes. Modal parameters, including natural frequencies and loss factors, are estimated by operational modal analysis. Simulation cases are provided as initial validation. Experimental validation was performed using an experiment in which distributed forces are applied to a flexible structure via a series of electromagnets mounted on individual force gages to measure the applied forces.

The nickel-based Inconel 718 alloy, known for its high strength, hardness, and temperature resistance, is widely used in cutting-edge industries such as aerospace. However, after wire electrical discharge machining (WEDM), the alloy surface can experience varying degrees of thermal damage, leading to a significant deterioration in the service performance of manufactured parts. In this study, single-factor experiments were conducted on the nickel-based Inconel 718 alloy to investigate the effects of different machining parameters on the surface quality, material removal rate, and microstructure. Using Taguchi experiments, parameter combinations that achieved the maximum material removal rate and minimum surface roughness were obtained. Based on parameter optimization, multiple trimming strategies were employed to study the effects of multiple trimming on the evolution of the surface microstructure and mechanical properties of Inconel 718 alloy parts. The results showed that with an increase in the number of trimmings, the thermal damage to the surface gradually decreased. After multiple trimmings, the roughness average (Ra) value was reduced to 0.396 μm, the recast layer thickness was reduced from 9.035 μm to 0.92 μm, and the surface hardness approached that of the substrate, effectively removing the surface-hardened layer. The tensile strength of the samples after multiple trimmings increased by 52.2 MPa. The fracture strain of the main cutting was 63.1%, while that after multiple trimmings was approximately 67%. The stress required to fracture the sample increased, thereby enhancing the mechanical properties. The thickness of the brittle fracture zone at the fracture edge was reduced from 18.89 μm to 6.65 μm. The findings indicate that parameter optimization and multiple trimming strategies can improve the surface quality and mechanical properties of Inconel 718 alloy workpieces.

Glass fiber reinforced polymer laminated (GFRPL) composites are extensively used in the development of multiple loading and high performance engineering components. It consists of greater properties, such as enhanced strength-to-weight ratio, and exceptional thermal stability. This plays a vital role in advanced composite manufacturing, that includes automobile parts, aeroplane parts, spaceships, and sporting goods. During manufacturing, the polymeric laminates essentially require the joining procedure while assembling the structural applications; in such cases, the bolted joint is frequently used to connect the different structural components. In the structural design of two-component joints, the component is governed by the durability and joint strength rather than the component capacity. In the joint setup, many types of joints are used to connect the fibrous composite, i.e., adhesive joint, bolted joint, and riveted joint. This work enhanced the riveted joint efficiency of laminated composite plates. The neat GFRPL and modified GFRPL samples were developed at 1, 2, and 3 Wt.% loading of multiwall carbon nanotube (MWCNT). Herein, the effect of MWCNT on single-lap riveted joining behavior and feasibility was investigated. The lap joint aluminum blind rivet with a 5 mm diameter was used to join the two composites’ specimens. The tensile test of single lap riveted joint specimen, impact, and Shore D hardness tests were performed to analyze the composite’s shear strength, energy absorption, and hardness. The outcome showed that the MWCNT loading enhances the shear strength, ductility, and hardness. The findings revealed that the higher shear strength and maximum failure load capacity were obtained for GFRPL samples modified by 1 Wt.% supplement of MWCNT as compared to the neat GFRPL, 2 and 3 Wt.% samples. The net tension failure occurred between the hole and the structure’s side edges. Optimizing the geometrical configuration of the single-lap riveted joint helps reduce bearing failure and applied net tension. The analysis of the riveted joint revealed its potential for further structural applications. Further, the morphological investigation of the fracture surface of the tested specimens and the elemental composition of the developed nanocomposites was explored.

Development of lightweight armors is vital in order to provide ballistic protection in a more effective way. The weight of steel armor can be decreased significantly by setting a front ceramic layer on it. In this paper, the influence of utilizing SiC and Al₂O₃ ceramic front layer on the ballistic behavior of 4140 bainitic steel was investigated experimentally. All steel plates were initially subjected to the austempering treatment by applying the austenitization at 860 °C for 1 h and then holding in a salt bath at 343 °C for 50 min to get fully bainitic microstructure. And then, the laminated composites, consisting of SiC or Al₂O₃ front layer (50 × 50 mm in size) and bainitic steel backing layer, were prepared by joining these layers with an acrylic adhesive. After the mechanical and microstructural characterization of the bainitic steel, the ballistic shots were made using 7.62 × 51 mm AP projectile with an average speed of 788.4 m/s on both monolithic steel and layered armor samples for comparison. The samples, which stopped the bullet at normal impact condition without complete perforation or disintegration of the bainitic steel layer, were termed as successful. The bainitic steel achieved the ballistic protection at a thickness ≥ 14 mm but the use of SiC layer provided the weight saving of at least 42.9% and the Al₂O₃ front layer enabled the weight reduction of 28.6% in the armor with respect to the monolithic 4140 bainitic steel.

Dynamic force measurements are often corrupted by the structural dynamics of the surrounding support structure. Force reconstruction techniques aim to correct for these structural effects by using additional information such as a modal characterization of the structure, a finite element model of the assembly, or additional instrumentation. In practice, accurately measuring input forces to validate the techniques is often difficult or impossible. This work proposes a novel experiment that allows for measurement of the true input spatial force distribution acting on a structure for the purposes of experimentally validating force reconstruction techniques. In the proposed experiment, independently-controlled electromagnets are supported by force gages and used to excite a flexible structure. The reaction force from the electromagnet gives a measure of the applied forces over a given bandwidth, which can be used to validate force reconstruction techniques. This paper focuses on the design of such an experimental arrangement, and presents a numerical model which can also be used to validate force reconstruction techniques. Key components of this experiment are characterized to validate the measurements and methodology. The independently-controlled electromagnets can mimic different types of physical excitation forces, which allow for validation of various force reconstruction techniques aimed at niche applications. For example, the main application of the proposed experiment is to reconstruct unsteady fluid-borne forces generated on a flexible test structure. As such, a sample measurement mimicking forces generated by turbulent flow across a beam using electromagnets is provided.

In this study, a novel flexural fatigue testing apparatus was designed to evaluate the fatigue behavior of 3D-printed materials. The machine was validated using polylactic acid (PLA) 3D-printed samples and fiber-reinforced thermoformed polypropylene (PP). The investigation focused on the effects of varying infill percentages of PLA and fiber reinforcement in PP under constant deflection, in accordance with Newton’s third law. The results provided significant insights into the fatigue life of these materials, including stiffness degradation and damage accumulation, thereby confirming the machine’s efficacy. This research contributes to a deeper understanding of 3D-printed material behavior under cyclic loading and enhances the machine’s capability to assess both conventional and specialized plastics. Furthermore, we compared the indirect measurement of elastic modulus obtained from fatigue testing with direct measurements for various percentages of reinforced PP, demonstrating the feasibility of deriving elastic modulus from fatigue testing.

The objective of this study was to minimize the friction force within the deformation zone in the simple shear extrusion (SSE) process by utilizing the ultrasonic vibrations directly on pure copper samples. Modal analysis was conducted on two types of horns (cylindrical-exponential-cylindrical and cylindrical-conical-cylindrical) to determine an efficient concentrator. Two punch feed rates of 5 and 10 mm/min, a frequency of 20 kHz, and an amplitude of 15 micrometers were employed in this ultrasonic-assisted simple shear extrusion (USSE) method. The homogeneity of microhardness and microstructure was investigated in both SSE and USSE methods. The findings implied that during the initial pass of the SSE method, the mechanical and microstructural properties were improved by increasing the feed rate; however, no improvement in the microstructural homogeneity was observed in the same pass. In contrast, the USSE process demonstrated enhancements in the mechanical and microstructural properties at a lower feed rate. Furthermore, a significant improvement in the homogeneity of the microhardness and microstructure was reported in USSE due to the uniform distribution of strain under ultrasonic vibrations in the samples. This enhancement was achieved in the first pass of USSE, whereas it occurred in subsequent passes in the SSE method. The cylindrical-exponential-cylindrical horn exhibited a more significant role in improving the homogeneity and mechanical properties compared to the cylindrical-conical-cylindrical horn due to its good concentration and transmission of vibrations.