1,721,028 research outputs found
Effect of operating temperature on aged single lap bonded joints
Full text linkIn 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
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
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
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
Increasing of ENF bonded joints performance by design of laser surface texturing
No full textThe quality of a bonded joint is strongly linked to the surface treatment used for the adherends. Recently, many studies have showed the opportunity to use a CO2 laser for enhancing the mechanical properties of bonded joints in FRP. Nowadays, to optimize their process parameters and texturing represent a necessary step for the growth in this technology. In this work, an experimental and numerical study of the effect of laser texturing on end notched flexure (ENF) joints realized in CFRP has been developed. The laser texturing showed an important effect on the mechanical resistance of ENF joints, with an increase of at least 76% respect untreated ones. The numerical results showed a good agreement with the experimental ones. Therefore, it is possible to design of the laser texturing for optimizing the mechanical response of bonded joints
Uniformity of thickness of metal sheets by patchwork blanks: potential of adhesive bonding
Full text linkThe 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
Experimental investigation of hydrothermal ageing on single lap bonded CFRP joints
No full textComposite materials are increasingly being used in various field of engineering interest over recent decades. As an alternative to fastening, bonding is one of the most promising assembly techniques of composite materials since it allows a uniform distribution of forces, it has a greater ability to dampen vibration and it does not raise any problems of corrosion typical of metal fasteners. Currently the use of composite materials is limited by the incomplete knowledge of their behaviour in an aggressive environment. For example, the factors influencing the durability of the bonded joints are mainly temperature and humidity, but it is usually impossible to predict their effect without performing experiments. In this work is investigated how the hydrothermal ageing can affect the mechanical resistance of CFRP single lap joints. The parameters chosen for the activity consist in two types of adhesives (AF 163-2K film and EA 9309NA paste) and three ageing environments (thermal cycles from -28 °C to 85 °C in air, distilled water and salt water)
Influence of hydrothermal ageing on single lap bonded CFRP joints
No full textNowadays adhesives are widely used in structural applications, in particular for assembly composite materials. In fact, this technique allows to obtain a more uniform load in the joint, to realize a joint with a higher specific strength and to avoid drilling parts as in the case of bolted joints. However, the mechanical properties of bonded parts over time are not well understood if they are subjected to a more or less aggressive environment. Generally, the main factors of influence regarding the durability of bonded joints are humidity and temperature, but their effects are not always clear if these two factors act simultaneously. In this work the effect of hydrothermal ageing on the mechanical resistance of single lap bonded CFRP joints has been investigated. In particular two types of adhesives (AF 163-2K film and EA 9309NA paste) and three ageing environments (thermal cycles from-28 °C to 85 °C in air, distilled water and salt water) have been chosen for the activity
Crush core forming: An innovative technology to manufacture structural sandwich parts with variable thickness
No full textSandwich structures, constituted in honeycomb core and skin in composite material, are usually employed to produce parts having a constant thickness or simple shape. Indeed, sandwich components with complex shapes, curvature or varying thickness are costly to manufacture due to the preliminary machining operations required on the core prior the molding process. A novel approach to manufacture complex sandwich structures, knows as Crush Core Forming (CCF) process, consisting in press-forming simultaneously the core material and the skins into the shape is under study. Such a method is potentially able to increase the production rate and lowering the overall costs. The present work aims to develop an experimental route to produce sandwich panels by means of CCF process and build a FE model of the forming process and validate it against the experimental studies. Experimental study was conducted to derive the fundamental parameters and properties for core and skins to be added in the FEM model of the CCF process. After, the numerical model was implemented to simulate the forming of the core and skins. Finally, a laboratory scale sandwich part was produced to validate the model outputs and assessing the reliability of the proposed approach
Temperature analysis in fiber metal laminates drilling: Experimental and numerical results
No full textDrilling process of fiber metal laminates (FML) requires a proper design of the processing parameters to prevent the occurrence of several issues and minimize defects, which can be detrimental for the integrity of the parts. These aspects become more critical in dry machining used in aeronautic field. In this scenario, the monitoring of process temperature is crucial to obtain useful information for machining optimization since many critical factors, such as matrix burnout, fiber pull-out and delamination, depend on the heat generated during the machining. The aim of this work is to monitor the temperature measured on the tool and workpiece during dry drilling of Al/GFRP (GLARE) and Al/CFRP (CARALL) hybrid laminates. The influence of the cutting speed on the temperature trends was analyzed. Two different set-ups were designed to measure the temperature on the tool, near the cutting edge and on the flank, and inside the laminate, in both the metallic and the composite parts. In addition, a numerical model to analyze the process temperature trend during drilling has been developed. The increasing the spindle speed from 1500 to 8000 rpm resulted in a decreasing of maximum temperatures of approximately 10°C on the tool tip and on the flank for the GLARE, and of almost 20°C in the CARALL laminates. The numerical simulation also pointed that the temperature fields is dictated by the thermal properties of carbon and glass fibers: temperature profiles within the CARALL were found smoother than those observed in GLARE
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