101,992 research outputs found
Uniformity of thickness of metal sheets by patchwork blanks: potential of adhesive bonding
No full textThe sheet metal forming operations generally involve the production of parts characterized by a non-uniform thickness distribution. However, in some cases, a product characterized by a distribution of thicknesses that is as uniform as possible may be desirable. This result can be obtained by using multiphase processes or by subtraction or addition of material from the blank. In this work, which deals with the method for adding material, an innovative methodology has been proposed as an alternative to the welding process. Specifically, the methodology is based on the bonding of a patch (before the deformation process), on the base plate with a constant thickness, in the area that most suffers from the thinning caused by the forming process. In this way, it was possible to influence the deformation of the patchwork blank and its thicknesses distribution. Through finite element analysis, it was possible to study the formability of a patchwork blank by varying the thickness and size of the patch, in order to produce an axially symmetric component by stretching through a hemispherical punch. Preliminary experimental tests demonstrated the reliability of the bonding and the potential of this method to uniform the final thickness of the sheet
Lightweight structures: An innovative method to uniform the thickness of metal sheets by patchwork blanks
No full textMetal sheet forming is widely used in industrial field. Generally, the use of patchwork banks allows the manufacturing of a more uniform thickness of the formed parts. Often, they are obtained using welding techniques: in these cases, distortions and localized metallurgical transformations could have detrimental effects on the mechanical performance. Moreover, it is not possible to weld very thin patches. In this paper, an innovative approach based on bonded patches has been developed and investigated. In this manner, it is possible to adopt thinner patches, doing away with the problems arising from the welding process. Experimental tests showed the potentiality of using adhesives in forming processes to influence the thickness distribution. Moreover, the commercial code PAM-STAMP has been used for modelling the forming process. In this way, the effects of the thickness of the patch and the friction conditions on the strain state generated on the patchwork blanks have been investigated
Effect of operating temperature on aged single lap bonded joints
No full textIn recent decades, designers have increasingly focused on the stability of assemblies in composite materials over time, particularly when used in structural applications. The use of structural adhesives allows for realising assemblies without mechanical fasteners. In fact, bonding is an assembly technique that prevent corrosion, ensures uniform stresses in the joint, and grows the specific resistance of the assembly. The knowledge of the behaviour of bonded joint is necessary to ensure the reliability of this technique over time, especially in aggressive environments. The aim of this work consists in investigating the combined effect of hydrothermal ageing and temperature test on the lap shear strength of single lap joints realised in CFRP. The results showed a higher influence of the ageing on paste adhesive compared to film adhesive. However, the ageing, combined with the operating temperature, played a fundamental role on the shear strength of the bonded joints
Drilling of glare laminates: effect of cutting parameters on process forces and temperatures
No full textDrilling operations in fibre metal laminates (FML) require a considerable optimization activity of the machining parameters as a function of those used in drilling of its constituents, fibre reinforced polymers and aluminium alloy. The accurate choice of drilling parameters is essential to minimize any defects of machined surface and inside the material that may compromise the structural integrity of part: these aspects become more critical in dry machining used in aeronautic field. Several authors have studied FML drilling, but they focused their attention mostly on the cutting forces, torque, drill wear, surface quality and hole damage. Instead, very little literature exists about temperature field that develops during FML drilling and in particular, no numerical models have been developed to predict this issue. The aim of this work is to monitor the cutting force and temperature measured on the tool and workpiece during dry drilling of Al/GFRP hybrid laminates (GLARE). In particular, the trend of the thrust force and temperature according to the main process parameters has been analysed. In addition, a first numerical model for analysing the process temperature trend during drilling has been developed
Study of autoclave process to manufacture thermoplastic composites constituted by PP/flax fibers
No full textAutoclave processes are widely used from industries that produce thermoset polymer composite parts. However, these materials show sustainability issues as they are non-recyclable and produced by energy-intensive processes. The use of thermoplastic matrices reinforced with natural fibers can solve these problems; however the optimal use of this material is linked to the knowledge of the forming parameters. In this work, starting from semipreg sheets, the autoclave forming process for parts in flax woven and polypropylene is studied and developed: it represents a fundamental step to develop the use of these new eco-friendly materials starting from the wellestablished industrial knowledge, not only in terms of environmental sustainability, but also economic and social sustainability. First, working temperatures were determined by DSC and TGA; while optimal forming pressure were determined by ILSS tests
Diamond tool wear monitoring by sensory analysis in milling of absolute black granite
No full textDiamond tools suitable for machining operations of natural stones can be divided into two groups: cutting tools, including blades, the circular blades and the wires, and the surface machining ones, involving mills and grinders, that can be of different shapes. For the stone sawing process, the most adopted tool type is the diamond mill, whose duration and performance are influenced by various elements such as: the mineralogical characteristics of the material to be machined; the working conditions such as the depth of cut, the feed rate and the spindle speed; the production process of the diamond segment and the characteristics of both the matrix and the diamond, such as the size, the type and the concentration of the diamonds and the metal bond formulation hardness. This work allows to indirectly assess the wear of sintered diamond tools by signal analysis (in time and frequency domain) of the cutting force components acquired in the process. The results obtained represent a fundamental step for the development of a sensory supervision system capable of assessing the tool wear and hence to modify the process parameters in process, in order to optimize cutting performance and tool life
Influence of Laser Treatment on End Notched Flexure Bonded Joints in Carbon Fiber Reinforced Polymer: Experimental and Numerical Results
No full textSurface pretreatment for bonding is one of the most important steps for the manufacturing of a reliable bonded joint. In this paper, the effectiveness of an innovative pretreatment by CO2 pulsed laser for bonding Carbon Fiber Reinforced Polymer (CFRP) was investigated. End Notched Flexure (ENF) specimens were made with different densities of laser treatment, and the respective fracture toughness was obtained through the Compliance-Based Beam Method (CBBM). Furthermore, a cohesive model for simulating debonding processes was illustrated, and the cohesive parameters were obtained by an inverse method. The achieved results represent a fundamental step for the development of a numerical model useful for the determination of laser texturing as a function of the applied local stress into the bonded joint
CFRP laser texturing to increase the adhesive bonding: morphological analysis of treated surfaces
No full textSurface roughness of the adherends represents an important factor for manufacturing a reliable bonded joint in structural applications. In case of bonding of parts in carbon fibre reinforced polymer (CFRP), an increase of roughness parameters can be obtained with various techniques. In this paper, the morphology obtained from a CO2 laser texturing on CFRP laminates were investigated. CFRP laminates were manufactured and subjected to laser texturing with various densities. In particular, the densities of treatment have been defined as a function of the grid dimensions of the texture. Subsequently, non-contact measurements were carried out to evaluate the evolution of the surface roughness parameters as a function of the density of the laser treatment. Results showed a strong correlation between surface roughness and density of treatment. In conclusion, these results were compared with experimental tests, which showed that the mechanical performance for ENF bonded joints was limited only by the flexural mechanical resistance of the CFRP adherends. As a result of this work, the developed laser texturing approach is potentially able to increase the mechanical resistance in the function of the real local load acting on the complex bonded joint, optimizing time and cost process
Laser treatment surface: An innovative method to increase the adhesive bonding of ENF joints in CFRP
No full textRecently, many studies showed the opportunity to use a CO2 laser for treating the surfaces for structural bonding. In this work, a study on the effectiveness of a laser texturing on ENF bonded joints made with CFRP and epoxy adhesive has been developed. The experimental results showed that the use of this technology allows obtaining mechanical resistances of the bonded joints higher than 80% compared to untreated ones. Furthermore, a numerical model is proposed to forecast the response of the ENF specimens, and the numerical results are in good agreement with the experimental ones. This work represents a basis for the development of an innovative approach to design the laser texturing as a function of the applied stress
Mechanical Characterization of AA8006 Aluminum Alloy through Cold Free Forming Test
No full textIn this work, for the first time thin, sheets of AA8006 aluminum alloy, that are commonly used for food packaging, were mechanically characterized through an unconventional free-forming technique that was performed at room temperature. This technique constitutes an economically effective solution to determine the constitutive equation of a metal sheet subjected to two-axes stresses. This state of stress reproduces the behavior of the material during the forming process better than the more traditional tensile test, which involves uniaxial stress. Specifically, the material constants were determined by using a simplified analytical model applied to the results of the experimental tests of the free forming process carried out at room temperature and constant pressure. Therefore, the obtained material constant values were used to simulate the same free-forming tests using FEM. In conclusion, the numerical results were in agreement with the experimental ones, thus confirming the goodness of the developed numerical model
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