This article is the second in a two-part series. Read Part 1 to learn more about the fundamentals of structural adhesive technology, adhesive bonding mechanisms, and the development of Belzona 7311.
To evaluate the performance of Belzona 7311, a two-component metal bonding epoxy structural adhesive, a series of internationally recognised test methods were conducted to assess its adhesion strength, fatigue resistance, impact performance and structural durability. These tests demonstrate the suitability of the industrial adhesive for demanding metal bonding applications.
Experimental Procedure
1. Cleavage Adhesion – ASTM D1062
Cleavage adhesion is used to assess the bond strength of a structural adhesive when joining metallic two substrates under cleavage loading. This test evaluates the resistance of the metal bonding epoxy to stresses that act to separate the bonded joint.
The metal bonding epoxy Belzona 7311 was applied between two identical grit blasted metallic cleavage test pieces to create a fixed bond area of 125mm² of minimal bondline thickness.
The specimen was allowed to cure then attached to a 25kN tensometer using suitable grips. The tensometer then applies a load at a fixed rate of 1.3mm/min exerting a cleavage force on the specimen until bond failure. This test is repeated five times so an average force can be calculated.
2. Tensile Shear Adhesion – ASTM – D1002
Tensile Shear Adhesion or lap shear adhesion is used to determine the adhesive strength of a material when bonded between two ridged metallic substrates. Samples are 100 x 25.4 x 2mm and are overlapped lengthwise by approximately 12.7mm and bonded to a minimal bondline thickness with Belzona 7311.
The specimen was allowed to cure then attached to a 25kN tensometer using suitable grips. The tensometer then applies a load at a fixed rate of 1.3mm/min exerting a cleavage force on the specimen until bond failure.
A standard static Tensile shear adhesion test was conducted to determine the mean breaking stress – 24.17 MPa following this 35% of the mean breaking stress value is used as the mean stress in fatigue testing – 35% mean shear stress = 8.461 MPa (24.17 MPa x 35%)
3. Fatigue resistance – ISO 9664
Fatigue resistance defines the ability of a structural adhesive to withstand repeated cyclic loading without bond failure. For metal bonding epoxy systems used in industrial repairs, fatigue performance is a key indicator of long-term durability.
At four different alternating stresses, fatigue testing was conducted at 30Hz until failure:
- 80% = 6.8 MPa (8. 461 MPa x 80%) Stress amplitude cycles between
- 60% = 5.1 MPa (8. 461 MPa x 60%) Stress amplitude cycles between
- 57.5% = 4.9 MPa (8. 461 MPa x 57.5%) Stress amplitude cycles between
- 55% = 4.7 MPa (8.461 MPa x 55%) Stress amplitude cycles between
4. Impact Resistance – ASTM D256
Impact tests can be used to assess the toughness of the metal bonding epoxy, and its ability to absorb energy during plastic deformation. Brittle adhesives have low toughness as a result of the small amount of plastic deformation that they can endure. Tougher materials such as structural adhesives on the other hand can absorb greater energy during fracture and thus, have improved impact resistance.
The Izod impact test allows for samples to be tested in two forms: either ‘notched’ or ‘un-notched’ in our case the testing will be notched which has a V-shaped notch of approx. 2.5mm in depth with a total defect angle of 45° in the centre of a specimen sample with dimensions of 12.7 x12.7 x 65mm. The notch concentrates stress and allows measurement of crack propagation.
5. Non-standard testing: 3 Point Load Test
This comparative technique is used to assess the relative flexibility of structural adhesives when bonding metallic substrates. The procedure provides an indication of the ability of the industrial adhesive to accommodate structural movement before bond failure. In this test a mild steel panel of dissimilar dimensions
Plate 1 550 x 50 x 10 mm thick
Plate 2 225 x 50 x 10 mm thick
are stressed to the point the adhesive fails. The panel is held in position at two points, one at either end of the sample and is gradually stressed at a single point in the centre of the specimen via a hydraulic press as seen in figure 3. The greater the displacement i.e., the further the press travels until failure the more flexible the adhesive. The thickness of the adhesive will influence the degree of flexibility so analysis should be duplicated for repeatability purposes. In the case of this testing at the manufacturing stage the specimens were compressed by hand pressure only, to try and replicate ‘in field’ applications of achieving below the maximum bondline thickness of 2mm.
Testing results and discussion
The following results demonstrate the mechanical performance of Belzona 7311 as a metal bonding epoxy structural adhesive. Testing was undertaken using recognised ASTM and ISO standards to evaluate its suitability for structural repair applications subjected to static and cyclic loading.
1. Cleavage Adhesion – ASTM D1062
2. Tensile Shear Adhesion – ASTM – D1002
3. Tensile Fatigue Resistance – ISO 9664
From a mean breaking stress of 35% (8.461 Mpa), Belzona 7311 will survive 106 cycles at 56.6%, with an alternating stress amplitude of ± 4.791 Mpa = 13mpa to 3.67 Mpa
4. Impact Resistance – ASTM D256
5. 3-Point load test
Conclusions
Several conclusions can be drawn from the use of Belzona 7311 as a solution for the repair or maintenance of assets:
- Belzona 7311 offers high resistance to structures that are subjected to forces such as peel, cleavage, vibration, or cyclic loading. These include, but are not limited to, support brackets for fire deluge systems, internal and external fixtures on process equipment, wear pads and wind girders on storage tanks.
- As Belzona 7311 offers an array of additional practical features including ease of application, ability to hold its own structure when placed in vertical applications and superior adhesion to metallic substrates, the toughened epoxy can be used on structural support reinforcements, load transfer supports and metallic staircases and ladders.
- Plate bonding to repair thinning or through wall defects on areas such as pipe/piping, process equipment, storage tank floating roofs and platform decks can utilise Belzona 7311 as it offers high impact resistance and flexural properties.
- Belzona 7311 has been optimised for metal-to-metal adhesion and exhibits an extensive data list with over 20 tests solely based on adhesion. The performance data can be used for Finite Element Analysis (FEA) or simulations to aid in bond designing or qualification of the adhesive in areas that would normally be seen as high risk for standard epoxies such as handrails and walkways.
Contact Your Local Distributor to Learn More About Structural Adhesives
What is cleavage adhesion testing?
Cleavage adhesion testing measures the ability of a structural adhesive to resist forces that attempt to separate a bonded joint from one edge. This type of loading creates high stress concentrations and is commonly used to evaluate the performance of metal bonding epoxy systems in demanding structural applications.
What does tensile shear testing measure?
Tensile shear testing determines the maximum shear load that a bonded joint can withstand before failure. It is one of the most widely used methods for evaluating the performance of structural adhesives used for metal-to-metal bonding and provides an indication of the adhesive’s load-bearing capability.
Can structural adhesive performance data be used in engineering design?
Yes. Mechanical property data generated from recognised testing programmes can support engineering calculations, finite element analysis (FEA) and bonded joint design. This information enables engineers to evaluate the suitability of a structural adhesive for specific loading conditions and service environments.
Having joined Belzona in 2010, Ian Wade has cultivated a deep expertise in corrosion, coatings, and inspection services. Currently serving as the Technical Services Manager at Belzona’s headquarters in Harrogate, Ian has held various roles. These include Technical Services Engineer and Training Facility Team Leader, where he managed the day-to-day operations of the training facility and collaborated closely with technical and business development teams.
Ian’s professional journey has taken him across the UK and international waters, including stints in South Korea, China, the North Sea, and the Caspian Sea, performing both supervisory and hands-on inspection work. His practical experience extends to on-site applications using Graco spray pumps and hand-applied coatings, directly enhancing operational standards and safety.
Ian is an AMPP (NACE) Certified Coating Inspector Level 2 and is currently advancing his knowledge by pursuing a Bachelor of Engineering in Mechanical Engineering part-time at The Open University, expected to complete in 2027. He has written a number of technical articles including: Strengthening the Bond with Reliable Structural Adhesives and The Benefits of Protecting Storage Tanks with Sprayable, Polymeric Coatings. His commitment to technical excellence and his robust experience make him a valued leader and innovator in his field.
