Лако-красочные материалы — производство

Giorgio Gallio * Mariangela Lombardi,

Paolo Fino and Laura Montanaro

Politecnico di Torino, Department of Applied Science and Technology,

Torino, Italy

Abstract

Nowadays, adhesive bonding is increasingly exploited in industrial applications, especially in multi-material lightweight structures, for its ability to join dissimilar materials together. In order to overcome the limits related to the durability of adhesives exposed to harsh environmental conditions, adhesive bonding can be used in combination with other joining techniques. This chapter examines the hybrid interference fitted-adhesive bonded joint and some design aspects for its practical application in a case study: the automotive steel wheel. An experimental evaluation of the contributions of the adhesive and the interference-fit to the resultant resistance of the hybrid joint was carried out with particular attention to the phenomena occuring at the interface

Corresponding Author address: Email: gallio. giorgio@gmail. com.

level and the effect of the adhesive nature, its curing technology and its mechanical response. The outcomes of the laboratory analyses were validated in the steel wheel system. It was found that the adhesive contribution mainly affected the static resistance of the hybrid joint, and it was strongly related to the type of adhesive exploited. On the other hand, the interference-fit seemed to play an important role in governing the fatigue behaviour, especially in the wheel system.

Keywords: Interference fit, hybrid interface, mechanical properties of adhesives, joint design

Introduction

Adhesive bonding is a suitable technology to join dissimilar materials together and recently its exploitation has greatly increased in industry for bonding new hybrid lightweight structures (Amancio-Filho & Santos, 2009; Dillard, 2010; Petrie, 2007). The main drawback of adhesives is related to their durability in harsh conditions due to their polymeric nature. In fact, especially in outdoor environments, adhesive joints are susceptible to water and humidity (Adams, Comyn, & Wake, 1997; Kinloch, 1990; Petrie, 2007). Nevertheless, adhesive bonding can be used in combination with other traditional joining methods generating a hybrid joint with the aim of combining the advantages of the different techniques and trying to overcome their drawbacks (da Silva, Pirondi, & Ochsner, 2011).

The interference fit is a common technique to join cylindrical parts together. The most common joint geometry consists in a shaft fitted into a hub or a ring. In order to guarantee the coupling, an interference 5 exists among the hub and the shaft.

The pull-out strength of a solely interference fit joint depends on the pressure P between the hub and the shaft, the friction coefficient p, and the contact area A, according to the equation (Croccolo, De Agostinis, & Vincenzi, 2010; Croccolo, de Agostinis, & Vincenzi, 2011; Kleiner & Fleischmann, 2011):

(1)

Moreover, the radial pressure P is a linear function of the interference level according to the Lame’s thick walled cylindrical theory (Croccolo et al., 2010; Kleiner & Fleischmann, 2011).

In the hybrid interference fitted-adhesive bonded joint the presence of an adhesive into an existing interference fit design can lead to a considerable strength enhancement. Moreover, the adhesives fill the roughness of the mating surfaces bringing the real contact area between the two fitted components to 100 %, thus improving the stress distribution in the joint area (Abenojar, Ballesteros, del Real, & Martinez, 2013; Castagnetti & Dragoni, 2012; Dragoni & Mauri, 2002).

Considering that this hybrid joint is a combination of the adhesive bonding and the mechanical tightening based on friction, the first main object of the technical research was focused on the comprehension of the interaction of these two techniques. A useful method developed for this aim is based on the concept of the superposition of the effects (Croccolo et al., 2011; Dragoni & Mauri, 2000; Kleiner & Fleischmann, 2011). According to this idea, the resistance of the hybrid joint is provided by the sum of the contributions due to the friction forces and the adhesive ones along the joint area, as two variables computed independently, according to the equation:

Phyb = № + Taf ■ A (2)

where na is the static resistance of the adhesive and / is a correction factor dependent on different parameters such as the assembly technique, the geometry of the joint and the adherend materials.

It is important to underline that the superposition approach has been not always confirmed at the experimental level. In some cases, in fact, the total resistance of the hybrid joint increased as the pressure between the components rised, but with a different rate (Dragoni & Mauri, 2000, 2002; Sawa, Yoneno, & Motegi, 2001; Yoneno, Sawa, Shimotakahara, & Motegi, 1997). Dragoni and Mauri (Dragoni & Mauri, 2000, 2002) developed a micro­mechanical model able to explain this different behavior in the case of strong and weak anaerobic adhesives subjected to a clamping pressure. In addition, recently, a numerical model has been developed and validated on the basis of this micro-mechanical model (Castagnetti & Dragoni, 2012, 2013).

The static and dynamic mechanical behavior of the hybrid interference fitted-adhesive bonded joint has been investigated from the numerical and experimental point of view by various authors, taking into consideration the effect of different important parameters such as: the pressure between the components (Croccolo et al., 2010, 2011; Dragoni, 2003; Mengel, Haberle, & Schlimmer, 2007; a. Oinonen & Marquis, 2011; A. Oinonen & Marquis, 2011; Sawa et al., 2001; Sekercioglu, Gulsoz, & Rende, 2005; Sekercioglu, 2005;

Yoneno et al., 1997), the assembling technique employed (Croccolo, De Agostinis, & Mauri, 2013), the fitted position (Kawamura, Sawa, Yoneno, & Nakamura, 2003), the different materials involved (Croccolo et al., 2010, 2011; Mengel et al., 2007), the roughness of the surface (A. Oinonen & Marquis, 2011; Sekercioglu, 2005) and the use of either epoxy and anaerobic adhesives (Mengel et al., 2007; A. Oinonen & Marquis, 2011).

Generally acrylic anaerobic adhesives, also known as “retaining compounds”, are employed in interference fitted-adhesive bonded cylindrical joints, particularly for their suitable curing technology. Activated by metal ions present on the adherends, anaerobic adhesives are able to cure in absence of oxygen, as it happens in a tightly closed joint (Comyn, 1997; Moane, Raftery, Smyth, & Leonard, 1999; Petrie, 2007). In fact, anaerobic acrylics have been effectively used as blockers and sealants, to improve the performance of mechanical tightening joints especially in the automotive industry (Dragoni & Mauri, 2000; O’Reilly, 1990). Nevertheless, in certain particular industrial applications other curing technologies could be more appropriate, especially in more complex joint geometries where both interference and clearance zones are included or different mechanical properties have to be matched. Considering these further potential applications, it should be important to understand the effect of the adhesive chemical nature, curing technology and mechanical properties on the performance of the hybrid joint.

This chapter completes the experimental results described in previous works (Gallio et al., 2014; Gallio et al., 2013) in order to better understand the effect of adhesive chemical nature, curing technology and mechanical properties on the press-fitted hybrid joint, and to further investigate the phenomena acting at the interference level and involving parameters related to tribology and rheology.

Finally, a case study describing the application of the hybrid interference fitted-adhesive bonded joint technique on the automotive steel wheel system is presented. The study was carried out in collaboration with the MW company, a division of the CLN group. The business of MW concerns the steel wheel market for passenger cars, light and heavy commercial vehicles and motorcycles. Bonded wheel prototypes were submitted to static and dynamic mechanical tests adopted for components validation. The results obtained on bonded wheel prototypes were compared with the traditional welded wheels and with the samples tested at laboratory level.