Tomas Walander 1, Anders Biel, Ulf Stigh

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Anders Biel, Ulf Stigh 1 Mechanics of materials, University of

1 AN EVALUATION OF THE TEMPERATURE DEPENDENCE OF COHESIVE PROPERTIES FOR TWO STRUCTURAL EPOXY ADHESIVES Tomas Walander 1, Anders Biel, Ulf Stigh 1 Mechanics of materials, University of Skövde, Box 408, Skövde, Contact tomas.walander@his.se Page 1

2 PRESENTATION AGENDA Motivation Measurement of cohesive laws Experimental study Evaluation of results Conclusions and summary Further work Acknowledgements Page 2

3 MOTIVATION Automotive industry Increase crash worthiness Reduce weight and thereby the emissions Combining high strength with low weight-materials Spot welds are often inappropriate Crash resistant structural epoxy adhesives Characterized by cohesive laws Temperature dependency Page 3

4 MEASUREMENT OF COHESIVE LAWS Deformation of an adhesive layer having an initial thickness t Peel σ = d J w, v dw J-integral, Energy release rate, w,v Shear τ = d J w, v dv Parameters of special interest: Fracture energy Peak stress Page 4

5 PREVIOUS STUDY Carlberger et.al. (2009), Int. J. Fract. Vol. 155 (2009) p. 155 DOW Betamate XW epoxy adhesive (BM1044), t = 0.2 mm Seven temperatures in the span - 40 T 80 o C Ten experiments in each temperature group Indications that the fracture energy is constant with respect to the temperature Decreasing peak stress with an increase in temperature. No studies of the temperature dependence in Mode II have been made Page 5

6 EXPERIMENTAL STUDY Mode I and Mode II experiments SikaPower 498 epoxy adhesive (SP498), t = 0.3 mm Five temperatures in the span - 40 T 80 o C Evaluation by statistical methods 1 st and 2 nd order regression analyses Coefficient of determination, R 2 R 2 = 1 good fit R 2 = 0 independence Kruskal-Wallis test Test variable, K 2 K < x g 1 independence 2 = 9.49 for g = 5 2 = for g = 7 x g 1 x g 1 The results in Carlberger et.al. (2009) are also re-evaluated by the statistical methods Page 6

7 + h + t MODE I EXPERIMENTS Double Cantilever Beam (DCB) specimen Specimen dimensions L = 160 mm b = 5.0 mm h = 6.60 mm t = 0.30 mm a = 80 mm 10 µm/s F F a L t + w Adhesive F, θ and w are measured and the cohesive law is measured by Adherends t h Page 7

8 MODE II EXPERIMENTS End Notch Flexure (ENF) Specimen Specimen dimensions L = 200 mm b = 10.0 mm h = 10.0 mm t = 0.30 mm a = 70 mm 0.5 mm/min (1 η) L F, θ and w are measured and the cohesive law is measured by d F ( v) (1 )sin 1 sin 2 sin 3 dv b Page 8

9 J c [kn m -1 ] J c [kn m -1 ] EVALUATION OF FRACTURE ENERGY 3.5 Mode I SP498, DCB DB1044, DCB Temperature [ C] Each point represent one unique experiment R 2 indicates a low level of explanation J I c for SP498 is independent of temperature Mode II The regression analyses shown an decrease with respect to the temperature for DB1044 in Mode I and for SP498 in Mode II. 0 SP498, ENF Temperature [ C] Page 9

Peak stress [MPa] Peak stress [MPa] EVALUATION OF PEAK STRESS 70 Mode I Mode II 60 50 40 30 20 10 0 70 60 50 40 30 20 10 SP498, DCB DB1044, DCB -40-20 0 20 40 60 80 Temperature [ C] Each point

10 Peak stress [MPa] Peak stress [MPa] EVALUATION OF PEAK STRESS 70 Mode I Mode II SP498, DCB DB1044, DCB Temperature [ C] Each point represent one unique experiment R 2 indicates a high level of explanation The regression analyses show a decrease with respect to the temperature for both adhesives and deformation modes Linear slope: 310 < β 1 < 350 kpa o C -1 0 SP498, ENF Temperature [ C] Page 10

11 CONCLUSIONS AND SUMMARY The cohesive properties for two structural epoxy adhesives are measured and evaluated J I c for SP498 is independent of temperature in the span - 40 T 80 C J I c for DB1044 and J II c for SP498 decrease with an increase in the temperature. The peak stresses for all adhesives decreases with an increase in temperature for both loading modes. For both adhesives and loading modes, the peak stresses are decreasing with the same linear slope. Page 11

12 FURTHER WORK Initial stiffness's Verification with FEM ACKNOWLEDGEMENTS Swedish Knowledge Foundation for financial support SAAB Automobile AB, for providing a climate chamber Mr. Gunnar Åkerström and Volvo Material Technology for help in performing the ENF-experiments Mr. Magnus Bredberg and Mrs. Marie Lundgren at the University of Skövde for help with the statistics Dr. Thomas Carlberger for providing experimental data Page 12

13 QUESTIONS? AN EVALUATION OF THE TEMPERATURE DEPENDENCE OF COHESIVE PROPERTIES FOR TWO STRUCTURAL EPOXY ADHESIVES Tomas Walander 1, Anders Biel, Ulf Stigh 1 Mechanics of materials, University of Skövde, Box 408, Skövde, Contact tomas.walander@his.se Page 13

Proceedings of the 28th Risø international symposium on materials science, 3-6 Sept 2007.

Proceedings of the 28th Risø international symposium on materials science, 3-6 Sept 27. INFLUENCE OF TEMPERATURE ON COHESIVE PARAMETERS FOR ADHESIVES Anders Biel 1 and Thomas Carlberger 2 1 University