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The effects of surface roughness on the strength of adhesively bonded cylindrical components
Journal of Materials Processing Technology 142 (2003) 82–86
The effects of surface roughness on the strength of adhesively bonded cylindrical components Tezcan Sekerc´ ¸ ıoˇglu a,∗ , Hikmet Rende b , Alper Gülsöz a , Cemal Meran a a
Department of Mechanical Engineering, Engineering Faculty, Pamukkale University, Denizli, Camlik, Turkey b Department of Mechanical Engineering, Akdeniz University, Antalya, Turkey Received 19 July 2002; received in revised form 8 November 2002; accepted 17 February 2003
Abstract The strength of adhesively bonded cylindrical components was affected by the various factors, which are diametrical clearance, type of assembly, type of material, operating temperature, loading type, surface roughness, etc. In this study, the effect of different surface roughness values on bonding strength was experimentally investigated and the results are discussed. The experiments were carried out for both static and dynamic loading conditions. Results showed that optimum surface roughness values were found in the range from Ra = 1.5 to 2.0 m. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Bonding strength; Surface roughness; Fatigue
1. Introduction Using various methods, such as abrasion and machining in a different direction, adhesion forces can be increased. Capillary forces and viscosity affect the dispersion of the adhesive into the pores of the material. Sancaktar and Gomatam [1] investigated the effect of surface roughness of materials (cold and hot rolled steel) on the load bearing capacity of joint and distribution of stress using single lap joints. Maximum static load bearing capacity has been obtained between Ra = 1.65 and 2.0 m. To investigate the effect of the surface roughness and adhesive thickness on the bonding strength, torsion fatigue was applied to cylindrical components (mild steel, Rm = 350 MPa) which were bonded with epoxy adhesive [2]. The experiments performed between Ra = 0.56 and 5.0 m and the maximum fatigue strength (on the condition of 15% of the static shear force and 0.17 mm adhesive thickness) has been obtained for Ra = 3.0 m. It was declared that mean stress was extremely dependent upon both the surface roughness and the thickness of the adhesive. Besides, the greater the surface roughness and the thickness of the adhesive was resulted the less shear stress value. When the adhesively bonded joint is being designed, it has been emphasized that surface roughness and adhesive thickness should be taken into consideration carefully. ∗
Corresponding author.
Lee et al. [3] have conducted fatigue experiments of cylindrical adhesively bonded joints. They found out a rapid decrease in the fatigue strength values over Ra = 2.5 m. Uehera and Sakurai [4] carried out three experiments which were tensile, shear and peel strength tests. An optimum surface roughness exists in the tensile strength. The optimum value was in the range from Ra = 3.0 to 6.0 m. No clear relationship was observed between the peel strength and the surface roughness. The relationship between the bonding strength and the surface roughness was explained by adhesion theory, surface area effect and notch effect due to the surface roughness. Shaid and Hashim [5] concluded that normal tensile stresses in the case of rough steel surface were lower than those in polished ones. This difference could be as high as 30%. Moreover, cleavage strength appears to increase with the roughness level and profile area of adherent surfaces. It has been stated that the surfaces to be adhered should not be very smooth in adhesively bonded joints. The notch effect of roughness on extremely smooth surfaces disappears and the surface roughness should be between Ra = 0.8 and 3.0 m [6,7]. As summarized above, the previous studies showed that there was not a clear relationship between roughness and bonding strength. The object of this work is to clarify the influence of the surface roughness on the bonding strength of cylindrical components loaded as static and dynamic.
0924-0136/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00463-1
T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
83
2. Test materials and experimental procedure TecQuipment SM100 universal test machine has been used in the experiments. The test machine with the capacity of 100 kN is capable of doing static and dynamic loading. It is made up of four main sections (Fig. 1). These are called loading unit, pump unit, load meter and control unit. The pictures of specimens are given in Fig. 2 and the stress application type has been shown in Fig. 3. The loading type given in ISO 9664 standard [8] has been used in this study (Fig. 4). This standard yields the fatigue
Fig. 3. Loading for shear test specimens.
Fig. 1. Main sections of TecQuipment SM100 universal test machine.
Fig. 2. Specimen set-up and dimensions for shear strength test.
test conditions of single lap joints which are adhesively bonded. The cylindrical specimens have been used for the adaptation to the joints of shaft and hub in the performed experiments. As there is no standard concerning the fatigue of cylindrical specimens, the standard of ISO 9664 has been taken as a reference. By adjusting the minimum and maximum force applied on the specimens by means of potentiometers located on the control unit, minimum and maximum shear stresses have been obtained. The joints exposed to these stress values were damaged in their particular cycle numbers. The numbers of load cycles were measured by means of the mechanical counter located on the control unit. General structural steel (S235JR—EN 10025) has been used in the experiments. The chemical composition of this material was given in Table 1. The effect of surface roughness on adhesive bonding strength was investigated for the different surface roughened specimens. The specimens were machined with a lathe. For each roughness values, different specimens have been used in order to keep the bonding gap constant.
Fig. 4. Type of loading stress [8].
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T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
Table 1 Chemical composition of test specimens Element (%) C
Si
Mn
P
S
Cu
Ni
Cr
Mo
Fe
0.188 0.135 0.578 0.023 0.058 0.177 0.111 0.067 0.012 98.65
The different surface roughness values have been obtained using the abrasive sandpaper with various mesh numbers (P100C, P220C, P400C, P600C, P800C). The surface roughness of machined specimens has been measured using a Mahr Perthometer M4Pi profilometer. Some values and graphics on measured surface roughness have been given in Fig. 5. The apparatus is capable of measuring some values such as Rz , Rt , Rmax besides Ra . The specimens were cleaned with Loctite 7061 which is general purpose cleaner for preparing surfaces to be bonded
Fig. 5. Graphs obtained from profilometer showing five different surface roughness.
T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
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Table 2 Test conditions Related standard Adhesive Surface cleaner Ambient temperature (◦ C) Adherent materials Diameter/length Clearance (mm) Number of specimen Test frequency (Hz) Minimum force, Fmin (N) Minimum stress, τ min (N/mm2 ) Maximum force, Fmax (N) Maximum stress, τ max (N/mm2 ) Mean stress, τ m (N/mm2 ) Stress amplitude, τ a (N/mm2 ) Surface roughness, Ra (m) Average static shear force, FR (N) Average static shear stress, τ R (N/mm2 ) Average cycle number, N
ISO 9664 Loctite 638 Loctite 7061 18 ± 3 Steel–steel 30/30 = 1 0.1 4 0.75 5000 1.76 25000 8.85 5.3 3.54 0.45, 1.5, 2.3, 3.2, 6.2 51300, 69900, 67500, 59700, 57300 18.15, 24.74, 23.89, 21.11, 20.26 72200, 105000, 98775, 92950, 87600
Fig. 7. Relationship between cycle number and surface roughness.
roughness on the number of loading cycles applied before failure is shown in Fig. 7. Eqs. (1) and (2) have been obtained by dividing the curve in Fig. 6 into two parts and regression analysis has been applied between static shear strength and surface roughness. Average static shear stress, in the range from Ra = 0.45 to 3.2 m is τR = 1.095R3a − 8.62R2a + 19.66Ra + 10.94
with adhesive. After the cleaning of machined specimens, Loctite 638 adhesive was applied on the shaft and then the shaft has been placed into the hollow tube. Then these bonded specimens have been left for curing for 24 h at the room temperature. Loctite 638 is an anaerobic adhesive with high strength. It can join cylindrical components up to 0.25 mm gap. It gives good strength results under the conditions of dynamic, axial and radial loading. It can be used for joining cylindrical components as gear, shaft and pulley [7]. ISO 9664 standard procedure was applied to bonded specimens. Experimental conditions have been given in Table 2. 3. Results and discussion Experimental results are shown in Figs. 6 and 7. The relationship between the static shear strength and surface roughness has been shown in Fig. 6. The effect of surface
Fig. 6. Relationship between static shear strength and surface roughness.
(1)
and in the range from Ra = 3.2 to 6.2 m is τR = −0.314Ra + 22.21
(2)
Similarly, Eqs. (3) and (4) have been acquired by dividing the curve in Fig. 7 into two parts. In the range from Ra = 0.45 to 3.2 m is N = 739.1R3a − 52 521R2a + 110 525Ra + 32 425
(3)
In the range from Ra = 3.2 to 6.2 m is N = −1981.48Ra + 99 885.18
(4)
From the above equations, the maximum static shear strength and load cycle numbers can be obtained for the surface roughness between Ra = 1.5 and 2.0 m. Without conducting any additional experiments, above equations can be used to calculate approximate bonding strength for different surface roughness. Range from Ra = 0.5 to 2.0 m (Rz = 6.3–10 m) yielded the highest load cycle numbers. Smooth surfaces (Ra = 0.45 m) yielded the lowest static shear strength and load cycle number values. It has been observed that as the roughness increases over the optimum range from Ra = 1.5 to 2.5 m, the strength values decreases. It can be concluded that similar results was acquired in the range between Ra = 1.5 and 3.0 m given for previous studies for static loading. The reason of minimum values for Ra = 0.45 m may be the fact that the mechanical interlocking disappear due to inadequate penetration of adhesive on smooth surfaces. When the surface roughness increases more then necessary, the strength values decrease again. It can be said that the thickness of the adhesive increases partly and the adhesive cannot spread on the substrate surface because of too much roughness. Therefore, insufficient wetting occurs and then
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T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
strength values decreases. In order to obtain the optimum wetting in the adhesive joints, the adherent surface roughness should be considered. 4. Conclusions In this research, the influences of surface roughness of the adherents on the adhesively bonded cylindrical components which were loaded static and dynamic have been investigated. From the experimental observations, the following conclusions may be made: 1. The low shear stresses are obtained for both of the very smooth surfaces (Ra < 1.0 m) and very rough surfaces (Ra > 2.5 m). 2. For high bonding strength, the optimum surface roughness were obtained in the range from Ra = 1.5 to 2.5 m. 3. For the same surface roughness, the static and dynamic loading had shown similar features. 4. The surface roughness should be considered during the design stage of adhesively bonded joints.
References [1] E. Sancaktar, R. Gomatam, A study on the effects of surface roughness on the strength of single lap joints, DE, in: Reliability, Stress Analysis, Failure Prevention Aspects of Adhesive and Bolted Joints, Rubber Components and Composite Springs, vol. 100, ASME, 1998, pp. 91–111. [2] J.W. Kwon, D.G. Lee, The effects of surface roughness and bond thickness on the fatigue life of adhesively bonded tubular single lap joints, J. Adhesion Sci. Technol. 14 (2000) 1085–1102. [3] D.G. Lee, S. Kım, I. Yong-Taek, An experimental study of fatigue strength for adhesively bonded tubular single lap joints, J. Adhesion 35 (1991) 39–53. [4] K. Uehara, M. Sakurai, Bonding strength of adhesives and surface roughness of joined parts, J. Mater. Process. Technol. 127 (2002) 178–181. [5] M. Shaid, S.A. Hashim, Effect of surface roughness on the strength of cleavage joints. I, J. Adhesion Adhesives 22 (2002) 235–244. [6] T. Sekercioˇ ¸ glu, The investigations of adhesively bonded joints behaviour under dynamic loading, Ph.D. Thesis, Pamukkale University, Denizli, Turkey, 2001 (in Turkish). [7] Loctite Worldwide Design Handbook, 2nd ed., Loctite Corporation 1998 (on CD). [8] ISO 9664, Adhesives—Test Methods for Fatigue Properties of Structural Adhesives in Tensile Shear, 1st ed., 1993.
The effects of surface roughness on the strength of adhesively bonded cylindrical components Tezcan Sekerc´ ¸ ıoˇglu a,∗ , Hikmet Rende b , Alper Gülsöz a , Cemal Meran a a
Department of Mechanical Engineering, Engineering Faculty, Pamukkale University, Denizli, Camlik, Turkey b Department of Mechanical Engineering, Akdeniz University, Antalya, Turkey Received 19 July 2002; received in revised form 8 November 2002; accepted 17 February 2003
Abstract The strength of adhesively bonded cylindrical components was affected by the various factors, which are diametrical clearance, type of assembly, type of material, operating temperature, loading type, surface roughness, etc. In this study, the effect of different surface roughness values on bonding strength was experimentally investigated and the results are discussed. The experiments were carried out for both static and dynamic loading conditions. Results showed that optimum surface roughness values were found in the range from Ra = 1.5 to 2.0 m. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Bonding strength; Surface roughness; Fatigue
1. Introduction Using various methods, such as abrasion and machining in a different direction, adhesion forces can be increased. Capillary forces and viscosity affect the dispersion of the adhesive into the pores of the material. Sancaktar and Gomatam [1] investigated the effect of surface roughness of materials (cold and hot rolled steel) on the load bearing capacity of joint and distribution of stress using single lap joints. Maximum static load bearing capacity has been obtained between Ra = 1.65 and 2.0 m. To investigate the effect of the surface roughness and adhesive thickness on the bonding strength, torsion fatigue was applied to cylindrical components (mild steel, Rm = 350 MPa) which were bonded with epoxy adhesive [2]. The experiments performed between Ra = 0.56 and 5.0 m and the maximum fatigue strength (on the condition of 15% of the static shear force and 0.17 mm adhesive thickness) has been obtained for Ra = 3.0 m. It was declared that mean stress was extremely dependent upon both the surface roughness and the thickness of the adhesive. Besides, the greater the surface roughness and the thickness of the adhesive was resulted the less shear stress value. When the adhesively bonded joint is being designed, it has been emphasized that surface roughness and adhesive thickness should be taken into consideration carefully. ∗
Corresponding author.
Lee et al. [3] have conducted fatigue experiments of cylindrical adhesively bonded joints. They found out a rapid decrease in the fatigue strength values over Ra = 2.5 m. Uehera and Sakurai [4] carried out three experiments which were tensile, shear and peel strength tests. An optimum surface roughness exists in the tensile strength. The optimum value was in the range from Ra = 3.0 to 6.0 m. No clear relationship was observed between the peel strength and the surface roughness. The relationship between the bonding strength and the surface roughness was explained by adhesion theory, surface area effect and notch effect due to the surface roughness. Shaid and Hashim [5] concluded that normal tensile stresses in the case of rough steel surface were lower than those in polished ones. This difference could be as high as 30%. Moreover, cleavage strength appears to increase with the roughness level and profile area of adherent surfaces. It has been stated that the surfaces to be adhered should not be very smooth in adhesively bonded joints. The notch effect of roughness on extremely smooth surfaces disappears and the surface roughness should be between Ra = 0.8 and 3.0 m [6,7]. As summarized above, the previous studies showed that there was not a clear relationship between roughness and bonding strength. The object of this work is to clarify the influence of the surface roughness on the bonding strength of cylindrical components loaded as static and dynamic.
0924-0136/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00463-1
T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
83
2. Test materials and experimental procedure TecQuipment SM100 universal test machine has been used in the experiments. The test machine with the capacity of 100 kN is capable of doing static and dynamic loading. It is made up of four main sections (Fig. 1). These are called loading unit, pump unit, load meter and control unit. The pictures of specimens are given in Fig. 2 and the stress application type has been shown in Fig. 3. The loading type given in ISO 9664 standard [8] has been used in this study (Fig. 4). This standard yields the fatigue
Fig. 3. Loading for shear test specimens.
Fig. 1. Main sections of TecQuipment SM100 universal test machine.
Fig. 2. Specimen set-up and dimensions for shear strength test.
test conditions of single lap joints which are adhesively bonded. The cylindrical specimens have been used for the adaptation to the joints of shaft and hub in the performed experiments. As there is no standard concerning the fatigue of cylindrical specimens, the standard of ISO 9664 has been taken as a reference. By adjusting the minimum and maximum force applied on the specimens by means of potentiometers located on the control unit, minimum and maximum shear stresses have been obtained. The joints exposed to these stress values were damaged in their particular cycle numbers. The numbers of load cycles were measured by means of the mechanical counter located on the control unit. General structural steel (S235JR—EN 10025) has been used in the experiments. The chemical composition of this material was given in Table 1. The effect of surface roughness on adhesive bonding strength was investigated for the different surface roughened specimens. The specimens were machined with a lathe. For each roughness values, different specimens have been used in order to keep the bonding gap constant.
Fig. 4. Type of loading stress [8].
84
T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
Table 1 Chemical composition of test specimens Element (%) C
Si
Mn
P
S
Cu
Ni
Cr
Mo
Fe
0.188 0.135 0.578 0.023 0.058 0.177 0.111 0.067 0.012 98.65
The different surface roughness values have been obtained using the abrasive sandpaper with various mesh numbers (P100C, P220C, P400C, P600C, P800C). The surface roughness of machined specimens has been measured using a Mahr Perthometer M4Pi profilometer. Some values and graphics on measured surface roughness have been given in Fig. 5. The apparatus is capable of measuring some values such as Rz , Rt , Rmax besides Ra . The specimens were cleaned with Loctite 7061 which is general purpose cleaner for preparing surfaces to be bonded
Fig. 5. Graphs obtained from profilometer showing five different surface roughness.
T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
85
Table 2 Test conditions Related standard Adhesive Surface cleaner Ambient temperature (◦ C) Adherent materials Diameter/length Clearance (mm) Number of specimen Test frequency (Hz) Minimum force, Fmin (N) Minimum stress, τ min (N/mm2 ) Maximum force, Fmax (N) Maximum stress, τ max (N/mm2 ) Mean stress, τ m (N/mm2 ) Stress amplitude, τ a (N/mm2 ) Surface roughness, Ra (m) Average static shear force, FR (N) Average static shear stress, τ R (N/mm2 ) Average cycle number, N
ISO 9664 Loctite 638 Loctite 7061 18 ± 3 Steel–steel 30/30 = 1 0.1 4 0.75 5000 1.76 25000 8.85 5.3 3.54 0.45, 1.5, 2.3, 3.2, 6.2 51300, 69900, 67500, 59700, 57300 18.15, 24.74, 23.89, 21.11, 20.26 72200, 105000, 98775, 92950, 87600
Fig. 7. Relationship between cycle number and surface roughness.
roughness on the number of loading cycles applied before failure is shown in Fig. 7. Eqs. (1) and (2) have been obtained by dividing the curve in Fig. 6 into two parts and regression analysis has been applied between static shear strength and surface roughness. Average static shear stress, in the range from Ra = 0.45 to 3.2 m is τR = 1.095R3a − 8.62R2a + 19.66Ra + 10.94
with adhesive. After the cleaning of machined specimens, Loctite 638 adhesive was applied on the shaft and then the shaft has been placed into the hollow tube. Then these bonded specimens have been left for curing for 24 h at the room temperature. Loctite 638 is an anaerobic adhesive with high strength. It can join cylindrical components up to 0.25 mm gap. It gives good strength results under the conditions of dynamic, axial and radial loading. It can be used for joining cylindrical components as gear, shaft and pulley [7]. ISO 9664 standard procedure was applied to bonded specimens. Experimental conditions have been given in Table 2. 3. Results and discussion Experimental results are shown in Figs. 6 and 7. The relationship between the static shear strength and surface roughness has been shown in Fig. 6. The effect of surface
Fig. 6. Relationship between static shear strength and surface roughness.
(1)
and in the range from Ra = 3.2 to 6.2 m is τR = −0.314Ra + 22.21
(2)
Similarly, Eqs. (3) and (4) have been acquired by dividing the curve in Fig. 7 into two parts. In the range from Ra = 0.45 to 3.2 m is N = 739.1R3a − 52 521R2a + 110 525Ra + 32 425
(3)
In the range from Ra = 3.2 to 6.2 m is N = −1981.48Ra + 99 885.18
(4)
From the above equations, the maximum static shear strength and load cycle numbers can be obtained for the surface roughness between Ra = 1.5 and 2.0 m. Without conducting any additional experiments, above equations can be used to calculate approximate bonding strength for different surface roughness. Range from Ra = 0.5 to 2.0 m (Rz = 6.3–10 m) yielded the highest load cycle numbers. Smooth surfaces (Ra = 0.45 m) yielded the lowest static shear strength and load cycle number values. It has been observed that as the roughness increases over the optimum range from Ra = 1.5 to 2.5 m, the strength values decreases. It can be concluded that similar results was acquired in the range between Ra = 1.5 and 3.0 m given for previous studies for static loading. The reason of minimum values for Ra = 0.45 m may be the fact that the mechanical interlocking disappear due to inadequate penetration of adhesive on smooth surfaces. When the surface roughness increases more then necessary, the strength values decrease again. It can be said that the thickness of the adhesive increases partly and the adhesive cannot spread on the substrate surface because of too much roughness. Therefore, insufficient wetting occurs and then
86
T. S¸ ekerc´ıoˇglu et al. / Journal of Materials Processing Technology 142 (2003) 82–86
strength values decreases. In order to obtain the optimum wetting in the adhesive joints, the adherent surface roughness should be considered. 4. Conclusions In this research, the influences of surface roughness of the adherents on the adhesively bonded cylindrical components which were loaded static and dynamic have been investigated. From the experimental observations, the following conclusions may be made: 1. The low shear stresses are obtained for both of the very smooth surfaces (Ra < 1.0 m) and very rough surfaces (Ra > 2.5 m). 2. For high bonding strength, the optimum surface roughness were obtained in the range from Ra = 1.5 to 2.5 m. 3. For the same surface roughness, the static and dynamic loading had shown similar features. 4. The surface roughness should be considered during the design stage of adhesively bonded joints.
References [1] E. Sancaktar, R. Gomatam, A study on the effects of surface roughness on the strength of single lap joints, DE, in: Reliability, Stress Analysis, Failure Prevention Aspects of Adhesive and Bolted Joints, Rubber Components and Composite Springs, vol. 100, ASME, 1998, pp. 91–111. [2] J.W. Kwon, D.G. Lee, The effects of surface roughness and bond thickness on the fatigue life of adhesively bonded tubular single lap joints, J. Adhesion Sci. Technol. 14 (2000) 1085–1102. [3] D.G. Lee, S. Kım, I. Yong-Taek, An experimental study of fatigue strength for adhesively bonded tubular single lap joints, J. Adhesion 35 (1991) 39–53. [4] K. Uehara, M. Sakurai, Bonding strength of adhesives and surface roughness of joined parts, J. Mater. Process. Technol. 127 (2002) 178–181. [5] M. Shaid, S.A. Hashim, Effect of surface roughness on the strength of cleavage joints. I, J. Adhesion Adhesives 22 (2002) 235–244. [6] T. Sekercioˇ ¸ glu, The investigations of adhesively bonded joints behaviour under dynamic loading, Ph.D. Thesis, Pamukkale University, Denizli, Turkey, 2001 (in Turkish). [7] Loctite Worldwide Design Handbook, 2nd ed., Loctite Corporation 1998 (on CD). [8] ISO 9664, Adhesives—Test Methods for Fatigue Properties of Structural Adhesives in Tensile Shear, 1st ed., 1993.