Project 1 - Basic mechanical properties for design

Objectives

• To establish methods for preparing bulk specimens of adhesives with structure and properties that are independent of thickness.
• To compare the mechanical property measurements on bulk and joint specimens.
• To define the most efficient methods for determining basic mechanical properties.

Principal findings

• A variety of adhesive types was studied: one and two Part epoxies, two Part polyurethanes and two Part acrylics. Bulk specimens may be manufactured from each of the adhesive types, however care is needed to keep the exotherm under control and prevent changes in material properties.
• If valid comparisons are to be made, it is necessary to post cure the two Part epoxy and acrylic systems to ensure complete curing has taken place.
• Significant errors are associated with the use of strain gauges for the measurement of tensile strain.
• Contact extensometers are generally suitable for accurate measurements of strains below 1%, required for the measurement of modulus values, but care must be taken to avoid any out of plane bending. With less tough adhesives, contacting extensometers may induce premature failure.
• Where the adhesive extends to strains greater than typically 10%, non-contacting extensometers are necessary for strain measurements.
• No significant variation in the tensile properties of polyurethanes and one or two Part epoxies, with thickness in the range from 0.5 to 4 mm, is observed.
• The tensile properties of bulk acrylic specimens are variable, which is probably due to difficulties in specimen preparation.
• While tensile tests are an important Part of the acquisition of design data, additional data that has been obtained under a different stress state is needed. For adhesives, shear tests are the most obvious means of generating this extra data. With suitable precautions, the' bulk torsion specimen, bulk Arcan specimen I, butt torsion specimen and thick adherend shear tests are suitable for measuring shear stress/strain data.
• Properties such as modulus and yield stress vary with time, frequency and rate of test, due to the viscoelastic nature of the adhesive. In the region of temperature where behaviour is significantly viscoelastic, the determination of modulus from a test carried out under constant strain rate is ambiguous. In addition, data derived using a simple analysis is different from data obtained via dynamic mechanical methods.
• Data can be interpreted and correlated across test methods using relationships developed to describe linear viscoelastic behaviour in polymers.

REPORTS
REPORT NO.	REPORT TITLE	ABSTRACT	NO. PAGES	SIZE (MB)	LINK
1	The Preparation of Bulk Adhesive Samples for Mechanical Testing	Show	51	5.535
2	Measurement of Strain in Bulk Adhesive Testpieces	Show	50	3.405
3	Tensile Behaviour of Bulk Specimens of Adhesives	Show	40	2.179
4	Working draft for an International Standard Adhesives - Methods for preparing bulk specimens. Part 1: low-temperature, two-Part systems	Show	11	0.544
5	Correlation of Modulus Measurements on Adhesives Using Dynamic Mechanical and Constant Strain Rate Tests	Show	31	1.98
6 Pt A	Test methods for determining shear property data for adhesives suitable for design. Part 1: Notched-beam shear (Iosipescu) and notched-plate shear (Arcan) methods for bulk and joint test specimens. Part A: Summary	Show	12	1.225
6 Pt B	Test methods for determining shear property data for adhesives suitable for design. Part 1: Notched-beam shear (Iosipescu) and notched-plate shear (Arcan) methods for bulk and joint test specimens. Part B: Full report	Show	105	11.05
8	Test methods for determining shear property data for adhesives suitable for design. Part 3: The thick-adherend shear test method	Show	89	5.509
8 Pt 3/1	Test methods for determining shear property data for adhesives suitable for design. Part 3/1: Summary of the thick-adherend shear test method
8 Pt 3/2	Test method for determining shear property data for adhesives suitable for design
9	Comparison of Bulk and Joinit Specimen Tests for determining the Shear Properties of Adhesives	Show	36	2.572
10	Final report for Project 1: Determination of Basic Mechanical Properties of Adhesives for Design	Show	24	1.626

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