A numerical study on the cold sprayability of carbon fibre reinforced composites

One of the open questions in cold spraying on fibre reinforced composites is the optimal thickness of the top layer to provide a suitable base for successful deposition of the metallic particles and at the same time to hinder the probable damage of the fibres. In this study, a detailed finite element model is developed to study the deformation of a single Cu particle deposition on to polyether ether ketone (PEEK) substrate reinforced with carbon fibres. A PEEK layer with 30, 40 or 60 μm thickness was considered on the top surface of the composite. The particle impact velocity was varied in the range of 300-600 m/s to analyse its effects on the induced deformations as well as the structural integrity of the critical carbon fibres. It is believed that the proposed model can provide a helpful tool for predicting the optimal conditions in the metallization of polymers using the cold spray technique

Adapting Shot Peening for Surface Texturing Using Customized Additive Manufactured Shots

Surface textures in engineering materials not only affect the reflective properties and aesthetics but if properly designed can modulate surface-related properties such as wettability, fatigue, wear, corrosion, and scratch resistance. Herein, a new surface texturing method is introduced based on the conventional shot peening process. Custom shots are designed, and their surface texturing capability is investigated on acrylonitrile butadiene styrene (ABS) polymer substrates. A finite-element model is developed to bombard the substrate using AISI 316 stainless steel customized shots. The generated unique textures are compared qualitatively by visual examination and quantitatively using the standard surface roughness parameters. As a proof of concept, preliminary experiments are performed using a candidate custom shot and a spherical shot to treat the ABS sheets. The results highlight the high potential of the shot peening technique paired with additive manufacturing for customizing the peening media to be used for surface texturing polymeric materials

2020 Proceedings of the 3rd International Conference on Trauma Surgery Technology in Giessen

The 3 rd event of the Giessen International Conference on Trauma Surgery Technology on October, the 17th 2020 was hosted on Zoom in accordance with the worldwide corona situation. Dr Mieczakowski, Dr Yu, and Wolfram drafted in 2018 from Jan’s apartment in Bremen the manuscript which was submitted to and approved for funding by the Deutsche Forschungsgemeinschaft (DFG). At that time, we had no idea what substantial changes the conferencing concept would require. This is why we would like to thank again Michele. She first planned this year’s event after the 2019 date and then in the spring of 2020 had to replan for the new situation

Numerical Modeling of Bond Formation in Polymer Surface Metallization Using Cold Spray

Surface metallization of polymeric materials using cold spray technology has gained increasing attention in the past decade. Experimental studies have evidenced multiple challenges of this process regarding continuity and homogeneity of the metallic deposits on polymer substrates. Modeling and simulation tools could be very helpful to assess the efficiency of different strategies suggested for improved deposition at a considerably reduced cost; nevertheless, the efforts to use numerical modeling in this sector have been less successful. Here, we develop a detailed finite element model for the cold spray deposition of metal particles on polymeric substrates to shed light on the underlying deposition mechanisms. The simulation results are compared with the literature experiments to establish the effectiveness of the proposed model. The developed model is able to capture the key phenomena involved in the deposition mechanism particularly the particle and substrate mechanical interlocking and substrate local melting. It is shown that a particle velocity threshold value should be exceeded to achieve an effective mechanical interlocking. The substate thermal domain and melting as well as the effects of particle velocity and size on deformation and particle anchorage are discussed

Structural Integrity of Metal Deposits Obtained Using Cold Spray Solid-State Deposition

In the field of solid state metal deposition, bonding is induced based on the kinetic energy of the process. Cold spray, as the main technology in this field, is a relatively novel technique for depositing thin and thick coatings as well as three-dimensional large components at high production rates. In this process, particles of powder feedstock are directed towards the substrate using a heated propellent gas at supersonic velocities. The successive impacts of the particles result in a robust bond with the substrate as well as the previously deposited particles. The flexibility, high production rate, and high deposition efficiency have made cold spray a promising candidate for a wide range of applications, ranging from functional coatings, and repair applications to the production of freestanding parts. Innovative applications require a certain level of mechanical properties to cope with the prescribed service regulations. In this article, state of the art and the recent achievements on the structural integrity of solid-state deposits by cold spray are reviewed. Special attention is devoted to the effects of processing parameters and pre- and post-deposition treatments on static mechanical properties such as adhesion and cohesion strength as well as fatigue performance of the deposits

Investigation of Surface Nanostructuring, Mechanical Performance and Deformation Mechanisms of AISI 316L Stainless Steel Treated by Surface Mechanical Impact Treatment

Nanostructured materials exhibit superior properties with respect to their bulk counterpart. Recently, a new processing method for surface nanostructuring of metallic materials called surface mechanical impact treatment (SMIT) was developed. In this study, the surface microstructural features due to the refinement process of AISI 316L stainless steel by means of SMIT and subsequent mechanical performance were investigated. The effects of SMIT processing parameters, i.e. ball size and treatment duration, were studied in terms of microstructural evolutions using X-ray diffraction, transmission electron microscopy, optical microscopy, and field emission scanning electron microscopy analyses, and mechanical properties through hardness and tensile tests. A gradient nanostructured surface layer was successfully formed on the surface of the treated samples. The mean grain size was measured to be similar to 20 nm in the topmost surface layer and increased with increasing depth. Microstructural examinations showed that the twins and their intersections (rhombic blocks) formed in the surface layers. It was found that the mechanical performance of the treated samples is effectively enhanced. The surface hardness of the treated samples increased about 3 times while the yield strength of the samples increased with increasing SMIT time and size of the ball up to 2.5 times. The grain refinement mechanisms, mechanical properties, and fracture behavior were subsequently analyzed and discussed

Evaluating the homogeneity of surface features induced by impact‐based surface treatments

Impact surface treatments are well‐known for their efficiency in enhancing the mechanical properties of metallic materials, especially under cyclic loadings. These processes, which encompass a wide range of surface treatments based on repetitive impacts of tools of various types, induce surface plastic deformation, compressive residual stresses, and grain refinement alter the surface roughness as a side effect. Thus, it is essential to have suitable indexes to quantify the surface features caused by the typically random nature of these treatments. Herein, we evaluated the rationality of using standard roughness parameters for describing the morphological characteristics of surfaces treated by shot peening as a representative and widely used treatment of the category. A detailed numerical model of the peening process was developed. The output data were elaborated to extract the surface roughness parameters following the standard procedures. The results revealed the validity of the surface roughness parameters to describe the topography of material treated with adequate surface coverage, also highlighting the necessity to use a set of parameters rather than the common practice of relying on single parameters. Not considering a comprehensive set of amplitude and spacing parameters can result in significant, inconsistent, and misleading results while comparing the performance of surfaces

Optimization of mechanical properties for pulsed anodizing of aluminum

Mechanical properties such as thickness, hardness, and wear resistance of an anodic oxide layer on aluminum must be high enough for industrial purposes. Due to burning phenomenon, hardness and wear resistance of anodic oxide layer decrease as the thickness of the layer increases. These properties of oxide layer fabricated by regular anodizing on aluminum in mixed sulfuric-oxalic acid electrolyte were optimized using pulsed currents. For this purpose, four variable response surface design (duty cycle, frequency, maximum and minimum current densities) was utilized. Desirability function was used to maximize thickness, microhardness and wear resistance of the anodic oxide layer. Wear resistance of the layer was measured by means of ‘pin on disk’ method according to ASTM G89 standard. The determined optimal anodizing conditions were: duty cycle = 65%, frequency = 326 Hz, imax = 3.5 and imin = 0.5 A/dm2, while the corresponding estimated responses values were 170 μm, 526 Hv0.1 and 2.12 × 10− 7 g/N.m for thickness, microhardness, and wear rate, respectively. Frictional behavior of optimized pulsed, and direct current anodic oxide layers was discussed in terms of friction coefficient and examination of worn surfaces

Compressive behavior of Zn-22Al closed-cell foams under uniaxial quasi-static loading

Zn-22Al alloy closed-cell foams were fabricated by melt foaming process using hydride foaming agent. The compressive properties were investigated under quasi-static condition. The structure of the foamed material was analyzed during compression test to reveal the relationship between morphology and compressive behavior. The results show that the stress-strain behavior is typical of closed-cell metal foams and mostly of brittle type. Governing deformation mechanism at plateau stage is identified to be brittle crushing. A substantial increase in compressive strength of Zn-22Al foams was obtained. The agreement between compressive properties and Gibson-Ashby model was also detected

Thermographic analysis of composite metallization through cold spray

Cold Spray is an innovative technology to create coatings through the impact of metallic particles on substrates. Its application to composites’ surfaces is recently attracting the attention of the scientific community thanks to the possibility to functionalize and improve their thermal and wear properties. Within this context, the generation of the first metal-to-composite layer is fundamental. This work presented an experimental investigation of a composite panel, reinforced with glass fibers and coated with aluminum particles. The coating investigation was carried out through active pulsed thermography, analyzing the thermal response of single and double hatches. The thermal outputs were compared with a standard microscopic analysis, with a critical discussion supporting the identification of factors that influence the thermal response to the pulse: (1) layer’s thickness; (2) cold spray coverage; (3) layer compactness; (4) particle-substrate adhesion; (5) particle’s oxidation; and (6) surface roughness