Strengthening the Bond with Reliable Structural Adhesives



When identifying solutions that can offer assurance and longevity, the maintenance and reliability of assets repairs can be challenging, this white paper will look into the use of structural adhesives as the first-choice solution.

Structural adhesives can be used for affixing metal substratesor components as they provide high modulus and high strength. However, they are not currently internationally recognised like the traditional methodseven though adhesives are already used in a wide range of industries, such as aerospace, rail, and construction.

Traditional practice such as welding, riveting, nuts and bolts and mechanical fixing are perceived as the go to method.However, they all have their inherent inadequacies. Welding can be hazardous to health, riveting,nuts and bolts concentratethe stress locally while mechanical fasteners can concentrate stress.

This paper introduces a novel, two-component, solvent-free toughened epoxy adhesive material that provides high adhesion to metallic substrates while also being able to withstand high movement or cyclic fatigue in comparison to general epoxy materials.

As well as potential application areas, the article also discussesa number of benefits, including ease of use, load bearing andimpact resistanceproperties.


Most industrial maintenance or repair procedures can eitherinvolve welding or use of mechanical fasteners as these can be perceived as easy andquicker, however, these procedures might initially seem to correct the issue but may cause more harm than good.Depending on the repair situation for instance welding or drilling to connect mechanical fasteners on a storage tank containing flammable liquid is not recommended for obvious reasons this is where a structural adhesive can really offer a solution for that maintenance repair.

There are many structural fixings used across a whole range of industries that may be part of any maintenance or repairthese include support brackets such as cable trays, antennas, heating coils filter pans or any other internal fixtures in vessels that’s suffer from corrosion, impact orvibration damage. Within construction there are fire water deluge systems, nozzles connections, facades panels and signs which can require maintenance overtime or adverse weather conditions.

Processequipment or piping can suffer from thinning or the steel or even through wall defects which will need either monitoring or repairing depending on whether the integrity of the equipment has been lost.

Structural fittings are generally for fixing of static members but maybe subjected to forces unbeknown at time of installation this could include thermal cycling of the joints, cyclic loading or vibration due to fatigue of a component.

If there are repairs due to the above, the contractor maybe in asituation where a choice of solution can be made, then the strengths and weaknesses need identifying.

Welding is regularly used for repairs as it is widely available while being well regulated with high customer confidence and high strength of the repair it does come with its inherent risks both the use, the material by heat stressingand the user as welding can cause both acute and chronic health risks.Application of welding repairs onto live piping sections, storage tanks or process systems and equipment should not be undertakendue to the high temperatures involved and not forgetting the combustible nature of the process fluid or gasrunning through or being stored in these components.

Bolted joints are seen as simple and low cost due to the ease ofdisassembly and reassembly and these can be dissimilar metals,but the use of dissimilar metals will contribute to galvanic corrosion, add weight to the jointrequiring routine inspection and tensioning while the drilled holes in the support material, stress distribution is not uniform and concentrated at the holes.

Structural adhesives have high bond strength whilst being lightweightadhesive applied to cover the entire joint, resulting in uniform stress distribution, reducing metal distortion under strain.

Importance of a Strong Bond

Adhesive bonding is the joining of similar or dissimilar members together while creatingpermanent high strength bonds which can transfer structural stress without loss of structural integrity.

Regardless of the joint type used, it is important to understand the different stresses that are imparted onto a bonded assembly. Adhesives perform the best when the stress is two-dimensional to the adhesive, allowing the force to be applied over the entire bond area.

Joints that are well designed for adhesives place most of the stress into compression or shear modes, adhesives perform the worst when stress is one-dimensional to the adhesive, concentrating the load onto the leading edge of the bond line. Joints placing stress into cleavage or peel concentrate the stress onto the leading edge, which may lead to premature bond failures, especially if subjected to vibration, impact or fatigue

Bonds of high strength are obtained after cleaning of the substrate by removal of any contaminants followed by the roughening of the substrate generally in the form of grit blasting to international recognised standards, this is why surface preparation is critical to success regardless of what type of adhesive is used.

There are three types of bonding that are important to achieve to ensure good adhesion. These are:adhesive, chemical, and mechanical. 

Adhesive relies on surface energy to generate adhesion to the substrate. While chemical relies on chemical bond formation and electronic bonding to produce adhesion. Mechanical adhesion is due to the creation of an irregular profile that allows a deeper profile to be produced.

Thetypes of structural adhesivesavailable have been summarised in Table 1

Table 1 - Types of Structural Adhesives
B69470A1 3361 44C1 AE19 E0BCA6B6ABC4





There are two types of failure mechanisms associated with structural adhesives:

1. Cohesive failure occurs in the bulk layer of the adhesive material. This failure mode is limited by the strength of the adhesive material and can be caused by insufficient curing of the adhesive and applications at a greater thickness than that recommended among others.

2. Adhesive failure occurs when the mechanical adhesion between the adhesive and the parts being joined is overcome by the loading. This failure mode is associated with inadequate surface preparation, presence of contaminants, or insufficient curing of the adhesive among others. 


Design considerations for Belzona 7311 were based on both technical target requirements and a practicality approach, as summarised in Table 2.

70EB10E7 8E99 46E5 9639 CBE07511D58A










Table 2 - Design Considerations

Belzona 7311 was subjected to at least the following tests and evaluation protocols in to ensure that it met the design criteria previously discussed. Where possible, internationally recognised standards were used.

1. Cleavage Adhesion – ASTM D1062
2. Tensile Shear Adhesion – ASTM – D1002
3. Tensile Fatigue Resistance – ISO 9664
4. Impact Resistance ASTM D256


Experimental Procedure

1. Cleavage Adhesion – ASTM D1062

Cleavage adhesion is used to assess the strength of an adhesive bond between two substrates when exposed to cleavage stress.

Belzona 7311 wasapplied 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.

AAAF9C23 062E 444A BF78 EC4B3DF51525


















Figure 1 - Cleavage adhesion test

2. Tensile Shear Adhesion – ASTM – D1002

Tensile Shear Adhesion or lap shear adhesion is used to determinethe 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 tominimalbondlinethickness 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.

0424F58E 20C9 4587 8FCB 54C115D956DD

















Figure 2- Tensile force

3. Fatigue Resistance – ISO 9664

Fatigue resistance is the highest stress that a material can withstand for a given number of cycles without breaking.

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%)

08ECF5AE 799E 449A B565 B0A53CB56A2E

































Figure 3- Tensile shear adhesion test

At four different alternating stresses, fatigue testing was conducted at 30Hz until failure:

1. 80% = 6.8 MPa (8. 461 MPa x 80%) Stress amplitude cycles between 
2. 60% = 5.1 MPa (8. 461 MPa x 60%) Stress amplitude cycles between 
3. 57.5% = 4.9 MPa (8. 461 MPa x 57.5%) Stress amplitude cycles between 
4. 55% = 4.7 MPa (8.461 MPa x 55%) Stress amplitude cycles between 

Figure 4 - ISO 9664 Fatigue stress cycle

4. Impact Resistance – ASTM D256

Impact tests can be used to assess the toughness of a material, a material’s toughness is a factor of 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 on the other hand can absorb greater energy during fracture and thus, have improved impact resistance.

The Izodimpact 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°ithe centre of a specimen sample with dimensions of 12.7 x12.7 x 65mm. The notch concentrates stress and allows measurement of crack propagation.

Non-standard testing:

5. 3-Point Load Test

This comparative technique is used to assess the relative flexibility of adhesives when applied to a metallic substrate. 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 bondlinethickness of 2mm.

B6947687 DB63 4B79 AA08 8DA5CD9C59B7






Figure 5 3-Point Load Testing

Testing Results and Discussion

1. Cleavage Adhesion – ASTM D1062

Table 3 - Cleavage Adhesion Results - ASTM D1062

B6AC2191 ECD1 42D6 B04F E3F591F52D16




2. Tensile Shear Adhesion – ASTM – D1002

Table 4 - Tensile Shear Adhesion Results– ASTM D1002

6E4012EB 452D 4D36 80F5 DE704C112333



3. Tensile Fatigue Resistance – ISO 9664

Table 5 - Cyclic Fatigue Testing Results

FA996F2F 4746 4F04 907B 12CF2CD9F5E5




3C380B67 52F6 46E5 943E 13D6525ACCD6












Figure 6 - Belzona 7311 SN Curve

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

Table 6 - Impact Resistance Results – ASTM D256

28AAE308 CE2A 42DF BD68 8E370A6D8FBF





5. 3-Point Load Test

Table 7 3-Point Load Test Results

2694B08B 50F0 4257 A8D5 CC4593745F52







Figure 73-point load Specimen Testing


Several conclusions can be drawn from the use of Belzona 7311 as a solution for the repair or maintenance of assets:

1. 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 bracketsfor fire deluge systems, internal and external fixtures on process equipment, wear pads and wind girders on storage tanks.
2. 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 toughenedepoxy can be used on structural support reinforcements, load transfer supports and metallic staircases and ladders.
3. Plate bonding to repair thinning or through wall defectson 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.
4. Belzona 7311 has been optimised for metal-to-metaladhesion and exhibits an extensive data listwithover 20 testssolelybased on adhesion. The performance data can be used for Finite Element Analysis (FEA) or simulationstoaid 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.
AFEF0097 950A 42DE 86EC BAD19239E0BF




Figure 8 - Structural adhesive, Belzona 7311, used to bond bracket

Please click here for more information about Belzona 7311

Henkel offers comprehensive approach for assembly solutions

Successful assembly tasks rely on several key aspects:the equipment, automation expertisethe knowledge about adhesives and their application as well as on available professional support. Based on its longstanding expertise and its range of leading high-performance products and services under the well-known Loctite brand Henkel offers total assembly solutions that help customers to increase productivity, improve reliability and simplify design.

The Henkel portfolio includes comprehensive equipment for dispensing, light curing and robotics as well as a broad range of adhesive solutions focusing on bonding, sealing and coating. The company also offers extensive global support, technical expertise, on-site or remote training, and a full range of services. These services extend from integration and start-up support, through to calibration, field service, spare parts and consumables (needles, tips and nozzles), warranty support and a rebuild exchange program. Based on this holistic approachHenkel enables its customers to unlock new potentials in the global assembly market.

Over the past 30 years, the company has designed, built, and integrated advanced equipment solutions for uncountable customers. Regardless of the challenge  from water-thin liquids to high-viscosity pastes – Loctite equipment is capable of dispensing and curing a wide variety of adhesives, sealants and other industrial fluids, including acrylics, anaerobics, cyanoacrylates, epoxies, hot-melts, greases, inks, solvents and more. 

Available dispensing systems include anaerobic, bottle, cartridge, syringe and volumetric types, alongside dispense valves, and controllers and dispense reservoirs. The latest-generation reservoirs, for example, provide the effective dispensing of single-component Loctite adhesives at workstations, laboratories, and industrial installations. These units typically feature a dispensing valve for manual and benchtop applications, and a Loctite controller for semi- and fully automated processes. The compact design provides two independent digital timing channels that allow for the control of two pneumatic outputs to control dispense valves or any other pneumatic device. Loctite integrated dispensers also offer enhanced digital connectivity and precision pressure control for low viscosity dispensing applications. 

Loctite LED light-curing equipment includes flood-curing systems, spot-curing and handheld systems, as well as process control and monitoring systems. New-generation solutions provide high power, portability, continuous duty, and long life. These light sources offer optimal curing for the extensive Loctite line of UV/visible light-curing adhesive products, providing customers with a best-practice solution for their process needs.

Another important element of Henkel’s total assembly solutions proposition is the Loctite range of automated robotic dispensing systems. These innovative systems simplify the dispensing of adhesives and sealants on to complex surface configurations, improving process efficiency, minimizing material waste and reducing manufacturing costs.

Based on the holistic approach Henkel offers the know-how and expertise for total assembly solutions that create value for its global customer base.


Henkel and DaniMer form alliance to deliver bio-based hotmelt adhesives for packaging

Henkel International - Press & Media Relations >> 

01/15/2013 - Düsseldorf / Germany

Henkel, one of the leading adhesive companies, and DaniMer Scientific, LLC, a recognized leader in bio-based material technology, announced today that they have formed an alliance to develop hotmelt adhesives that use bio-based raw materials. The initial target for these bio-based hotmelt adhesives will be the consumer packaging market including applications of end of line and labeling.

Manuel Neuer, keeper of the German national football team, teams up with Metylan

Henkel International - Press & Media Relations >> 
01/18/2013 - Düsseldorf / Germany

2013 sees 26-year-old Manuel Neuer, goalkeeper of the German national football team and Bayern Munich, at the heart of a German-wide advertising campaign launched by Metylan, the internationally successful Henkel brand for wallpapering products. The motto of this team play: "Metylan for a perfect hold – just like our Number 1."

More sustainability accolades for Henkel

Henkel International - Press & Media Relations >> 
01/28/2013 - Düsseldorf / Germany

Henkel has been honored a further three times as a leading proponent of sustainability in its sector – both within Germany and in comparison with its international peers. And the company has also taken top positions in recent online sustainability communication rankings.

Henkel presents awards to outstanding suppliers

Henkel International - Press & Media Relations >> 
01/31/2013 - Düsseldorf / Germany

At the 2013 American Cleaning Institute (ACI) Annual Meeting and Industry Convention, January 28 through February 2 in Orlando, Florida, Henkel recognized five suppliers for their outstanding cooperation. The “Best Innovation Contributor Award” was conferred to Novozymes and Dow Corning. Prize winners of the “Henkel Sustainability Award” were Monosol and Evonik Industries. The “Best Supply Performance Award” went to Ashland.

New type of paste with enhanced thermal conductivity for modules

Henkel International - Press & Media Relations >> 
02/14/2013 - Düsseldorf / Germany

Power electronics are experiencing a continuous rise in their power densities. As a consequence, thermal management for today’s power semiconductors must be integrated as early as their design phase. Only then can reliable cooling be safeguarded over the long term. A particularly important role is assigned to thermal conduction at the link between the component and the heat sink. In these cases, materials are often used that cannot meet the growing requirements. In its search for a remedy, Infineon Technologies AG has incorporated a TIM material solution from Henkel Electronic Materials to now make available a heat conducting compound optimized specifically for the architecture of power semiconductors in modules.

New branding architecture for the Henkel adhesive technologies business serving industrial markets

Henkel International - Press & Media Relations >> 
02/19/2013 - Düsseldorf / Germany

Henkel will introduce a new branding approach for its industrial adhesive technologies business. The company’s brand portfolio has grown strongly over the past decades and has enabled Henkel to become the global market leader in adhesives, sealants and surface treatments. To improve the navigation through the brand portfolio, Henkel will now re-group its industrial business for adhesive technologies under five technology cluster brands, each of which will represent a cluster of specific technologies and applications.

Henkel to acquire Polish Laundry and Home Care brands from PZ Cussons

Henkel International - Press & Media Relations >> 
02/20/2013 - Düsseldorf / Germany

Henkel has signed an agreement with the UK-based consumer products company PZ Cussons Plc to acquire their Polish Laundry and Home Care brands. The transaction includes predominantly detergents and fabric softeners of the “E” brand, and other smaller brands. The business operates mainly in Poland but also includes activities in Russia and other Central Eastern European countries.

Frekote for high-gloss plastic components

Henkel International - Press & Media Relations >> 
02/25/2013 - Düsseldorf / Germany

The Frekote products that Henkel will exhibit at the JEC Composites fair are highly efficient solutions for complex mold geometries. During the exhibition centering on the composites industry, which takes place from March 12 to 14 in Paris, the world’s leading adhesives manufacturer will present its product portfolio for the sector. Frekote is not only the brand for outstanding mold release agents; users also benefit from Henkel’s expertise in the development of customer-specific solutions.

Working together for sustainability

Henkel International - Press & Media Relations >> 
03/06/2013 - Düsseldorf / Germany

Henkel is publishing its latest Sustainability Report today. The focus of this 22nd issue is on the implementation of the sustainability strategy that the company presented in 2012. At the core of the strategy is the goal of achieving more with less. Henkel intends to triple its resource efficiency by the year 2030. To achieve this ambition, Henkel is actively involving its employees in its strategy implementation programs and working with its partners to drive sustainability along the various value chains. 

This website is owned and operated by: MSL Media Limited

msl logo

Co. Number: 05359182

© 2022 MSL Media Ltd. All rights reserved. E&OE

ems logo mobile