The Effect of Different Adhesive Types on Failure Load

Abstract

In this study, bonding joint with double zigzag type geometry was used. There are four types of overlap angles in the bonding geometry: 30°, 45°, 60° and 75°, respectively. Composite materials that are made of glass fiber have been used in this adhesive bonding geometry. These materials were produced by using prepreg (pre-impregnated) technique and [0°/90°] of orientation angle. Thickness of composite material is 3 mm. Ductile and brittle-type adhesives were used for the bonding joint. DP460 adhesive type shows ductile material properties while ATLAC580 adhesive type shows brittle material properties. The effect of adhesive type on the failure load was investigated experimentally. Test results demonstrated that failure load values were higher in the ductile-type adhesive.

1. Introduction

Industrial adhesives are a joining method used as an alternative to mechanical joining methods such as bolts, rivets, welding, and soldering. They have found a suitable area for development, as the bonding process is carried out below the melting temperatures of the joined parts. In addition, industrial adhesives do not create stress concentrations that occur in welding, soldering, and other connection types. The use of industrial adhesives, which are used as an alternative to existing bonding methods, is rapidly increasing. There are many applications joining with adhesive, especially in the aerospace, aviation, and automotive industries.

In this study, a mechanical analysis of the bonding joint geometry was realized using different types of adhesives.

The use of adhesive, which is a more efficient joining method, has become common instead of traditional joining methods [1]. An adhesive is defined by ASTM (Standard test method for strength properties of adhesives in shear by tension loading) as “a substance that can hold materials together by surface contact” [2]. In another definition of adhesive, it is a polymeric material that can hold surfaces together and prevents separation when applied to surfaces [3]. Neto et al. [4] carried out an experimental study on the bonding joint of composite materials. They used two different adhesives, brittle and ductile type in a single lap joint with different lap lengths between 10 and 80 mm. It was seen that failure load increased with growing overlap length in the ductile-type adhesive joint. It was determined that 30 mm overlap length failure load occurred in the brittle-type bonding joint. Sawa et al. [5] analyzed the single lap joint formed by different types of adhesives subjected to tensile loads. They showed that the material thickness and the modulus of elasticity have an extremely large influence on the stress distributions in bonding area. Guess et al. [6] studied analytically and experimentally the strength of adhesively bonded single lap joints using two different adhesives. Apalak et al. [7] made analysis on corner joints. Adhesive is considered as a linear elastic material, and its effects on the bonding stresses created in corner joints were investigated.

Pinto et al. [8] experimentally investigated the mechanical behavior of single lap joint under tensile load by using two different adhesives, rigid and flexible. They stated that there was an insignificant decrease in the strength of the joint in the flexible adhesive type, but there was an increase in the bond strength when rigid adhesive was used. Ozel et al. [9] carried out an experimental study on a single lap joint under bending load using two different types of adhesives. They demonstrated that thickness of material has an extremely major effect on bonding joint performance. Wu et al. [10] applied a method they developed on single lap joints formed using different adhesives of different thicknesses. Temiz [11] stress analysis was performed using a flexible and rigid adhesive on single lap joint. It has been shown that the use of flexible adhesive reduces stress concentrations and increases the strength on the bonding joint. Kline [12] studied the effect of thickness on stress distribution in bonding layer. The alteration of stresses along the thickness is considered linear. He investigated the effect of parameters on the stress distribution in the bonding layer. Dean and Duncan [13] prepared bulk samples with thicknesses varying between 0.5 and 4.0 mm and examined whether the mechanical properties of the adhesive change with thickness. They used four different types of structural adhesives. One and two component epoxies, two-component polyurethane, and two-component acrylic adhesives were tested on samples with different thicknesses. According to the tensile test results, they determined that the material properties did not change with the sample thickness.

The goal of this study is to experimentally analyzed the effects of Vinylester Atlac 580 brittle-type adhesive produced by Huntsman Company and DP460 ductile-type adhesive produced by 3 M Company on failure load.

2. Material and method

DP460 is the center formed by epoxy and accelerator in a 2:1 volume ratio. It is used in a facility from metal, ceramics, and glass.

ATLAC 580 is a low-viscosity epoxy-based vinylester resin that is heat-resistant and flexible. It can also be used for wrapping and spraying in fabrication methods. It is resistant to acid and salt solutions. It is cured with accelerator and hardener mixture.

Curing conditions of brittle type of ATLAC580 and ductile type of DP460 adhesives used in the experiment are given in Table 1.

Type of adhesive	Component	Curing conditions	State
ATLAC580	Epoxy/accelerator	120°C/60 min	Liquid
DP460	Epoxy/accelerator + hardener	100°C/180 min	Liquid

Table 1.

Curing conditions of adhesives.

The mechanical properties and stress-strain diagram of DP 460 adhesive are taken from Akpınar’s [14] doctoral thesis. Also, the mechanical properties and stress-strain diagram of ATLAC 580 adhesive are taken from Adin’s [15] doctoral thesis as given in Figures 1 and 2.

Figure 1.

Stress-strain diagram of DP 460 ductile adhesive

Figure 2.

Stress-strain diagram of ATLAC580 brittle adhesive.

The mechanical properties of ATLAC580 and DP460 adhesives used in the experiment are given in Table 2.

	DP 460	ATLAC 580
Modulus of elasticity; E, Mpa	2077.10	442.46
Poisson’s ratio; ʋ, (−)	0.38	0.37
Max. Tensile Stress; σ, Mpa	44.615	40.618

Table 2.

Mechanical properties of ductile and brittle adhesive.

The high strength of adhesive bonding joint depends on surface preparation methods. The samples must be cleaned from foreign materials such as oil, dirt, and dust that will prevent adhesion. The surfaces were first washed with pure water and then wiped with microfiber cloths. Then, the surfaces to be bonded with pure alcohol were washed and kept on hold until the alcohol exactly evaporated from the surfaces.

Consistency of the adhesive thickness on the surface is possible with the use of a well-designed mold. For this, the thickness of the adhesive was kept constant at 0.20 mm so that the sample length is kept constant, it was placed in a certain mold.

2.1 Experimental study

The composite plates used in the experiments were cut in CNC milling device in accordance with ASTM standards and in desired geometric dimensions. The length of each test specimen is 250 mm. About 25 mm jaw margin is left for the specimens to be fixed to the tensile test device.

Glass fiber composite materials were used in the experiment. Glass fiber-reinforced composite materials are produced as prepreg (pre-resin-impregnated wet fiber). Composite materials were prepared for testing with a sample thickness of 3 mm and fiber orientation [0°/90°] and are given in Figure 3.

Figure 3.

Composite samples with four different overlap angles.

In the experimental study, four different types of adhesive joints with overlap angles of 30°, 45°, 60° and 75° were used as seen in the Figure 3. The bonding length of each angle was kept constant at 60 mm.

The Shimadzu AG-X model tensile test device was used in the experiment (Figure 4). The device has an integrated extensometer and with a capacity of 100 kN.

Figure 4.

Tensile test device and composite sample.

The test device was calibrated before it was started. The test device was given a preload of 0.10 Mpa. Experimental tests 1 mm/min carried out at pulling speed as seen in the Figure 4. The experiment was terminated after the samples were completely detached from the bonding area.

2.2 Experimental results

Tensile tests were performed at four different overlap angles. Composite materials are produced in [0/90°] fiber orientation and 3 mm sample thick. Failure load values of each sample were determined by experiment. For the precision of these values, three samples of the same bonding type were produced, and the test was repeated. Results in graphs are the average of three test specimens.

Failure load and displacement graphs for DP460 (ductile) and ATLAC580 (brittle) adhesives are shown in Figures 5–8.

Figure 5.

Failure load-displacement graph for ductile and brittle adhesive at 30° angle.

Figure 6.

Failure load-displacement graph for ductile and brittle adhesive at 45° angle.

Figure 7.

Failure load-displacement graph for ductile and brittle adhesive at 60° angle.

Figure 8.

Failure load-displacement graph for ductile and brittle adhesive at 75° angle.

Failure loads increased with increasing overlap angle in the same bonding area. Increasing the overlap angle increased the failure load by approximately 81%. The highest failure load value was observed at 75° overlap angle. Test results demonstrated that failure load values were higher in the ductile-type adhesive.

Failure load and displacement graph for entire overlap angles for DP460 (ductile) adhesive is shown in Figure 9.

Figure 9.

Failure load-displacement graph for all overlap angles for ductile adhesive.

Failure load and displacement graph for all overlap angles for ATLAC580 (brittle) adhesive is shown in Figure 10.

Figure 10.

Failure load-displacement graph for all overlap angles for brittle adhesive.

The failure load values of the ductile-type adhesive were bigger than the failure load values of the brittle-type adhesive. Modulus of elasticity of the ductile-type adhesive is 2077.10 MPa, while the modulus of elasticity of the brittle-type adhesive is 442.46 MPa.

As a result of the experimental study, it has emerged that the adhesive type has a significant effect on the failure load.

When the whole graphs of both adhesive types were examined, more displacement was obtained in the ductile-type adhesive, while almost half of this amount of displacement was obtained in the brittle-type adhesive.

When the bonding surfaces were examined, cohesion damage was observed in the ductile type of adhesive, and adhesion damage was observed in the brittle type of adhesive.

3. Conclusions

In this study, glass fiber composite materials were used at different overlap angles and with different adhesive types by using a single lap joint exposed to tensile loads.

As a result of the experiment, it has been revealed that the failure load increases with the increase of the overlap angle value in the bonding joint geometry.

Cohesion damage was occurred in the ductile type of adhesive, and adhesion damage was occurred in the brittle type of adhesive.

In addition, it can be said that the ductile type of adhesive increases the strength of the bonding joint.