Material Testing for Adhesives

Owned by Tommy Tran
Last updated: Sept 23, 2020
5 min read

To do list for Fall 2020:

Find sufficient test materials (steel and CFRP)
Buy degreasing solvents from Home Depot in Waterloo
Machine test specimens
Prepare test specimens
Ask or email professors about using tensile test machines
Record and plot results
Make conclusions about true adhesive strength and effect of surface preparation on adhesive strength

Goals for Material Testing:

  • Validate adhesive strength, i.e. compare technical data sheet values with our manufactured values

  • Determining how much adhesive is required per surface area bonded

  • Determining the necessity of a degreasing solvent, i.e. a surface preparation technique

  • Determining the necessity of abrasion, i.e. a surface preparation technique

Research Phase of Material Testing

The purpose of material testing is to compare the performance of the adhesives produced from our manufacturing ability to the provided technical data sheets. This allows us to have a more realistic understanding of the strength of the adhesive and the quantity of adhesive spent to bond parts together.

The process of deciding on how to begin material testing is based on the provided properties in the adhesive’s technical data sheet (TDS). Each property, e.g. tensile strength, provided by the manufacturer has been tested using specific standards for material testing which will be described next to each property. It would be very important to then research the standards that the manufacturer has used to test their material so that we can conduct our own material testing that is similar to how their experiments were prepared. Note that it may be difficult to find the information on specific standards because they are publications that are sold online. If your research does not yield any literature results, it is possible to try to find the equivalent of a standard as has been done in this material testing for adhesives. It is also possible to find a generic and well-known method of testing for the property being examined which was also done in this material testing.

In terms of the adhesive, EA E-120HP has been examined to have two properties that were viable for material testing. The first property was the tensile strength (ISO 527-3) for the properties of the cured material. Literature on the testing standard was found, but this test involved manufacturing an adhesive film sample which seemed difficult and irrelevant to our application. The second property was the lap shear strength (ISO 4587) for the performance of the cured material. Literature could not be found on this testing standard and therefore research on an ASTM equivalent (D1002) and generic adhesive overlap shear strength test was found.

 

Plan for Adhesive Material Testing

The material testing will feature a single lap shear strength test which is a common and economic for testing overlap shear strength. This test is heavily similar to ISO 4587 (used in the TDS) and D1002 (the ASTM equivalent)


Table #1: Material, Curing Process, and Lap Shear Strength given from EA E-120HP Technical Data Sheet

Material

Curing Process

Lap Shear Strength (MPa)

Aluminum (acid etched)

Cured for 2 hrs @ 65 deg C

13.7

Steel (grit blasted)

Cured for 12 hours @ 65 deg C

30

Aluminum (acid etched & abraded), 0.1 to 0.2 mm gap

33

Aluminum (anodised)

14

Stainless steel

23

Polycarbonate

6.9

Nylon

2.3

Wood (Fir)

11.3

 

Single Lap Shear Test: (D1002, ISO 4587)

http://www.adhesivestoolkit.com/Docs/test/MECHANICAL%20TEST%20METHOD%201%20-%20Shear%20Tests.xtp#_Toc109014547

Specimen Preparation:

  • Two rectangular sections that are 25 mm wide, 100 mm long and 1.6 mm thick 

  • An overlap length of 25 mm.

  • Fixture is used to ensure correct overlap and accurate alignment of the adherend.

Equipment:

  • Testing can be conducted using standard tension/compression mechanical test equipment

    • Should ask the university (specifically E3) about the use of a universal testing machine (UTM) which is used to test tensile strength and compressive strength of materials.

 

Testing Procedures:

  • Prepare at 9 adhesive joint specimens following procedures from the product’s technical data sheet

    • 3 adhesive joints should be prepared without any significant surface preparation technique

    • 3 adhesive joints should be prepared using degreasing solvent

    • 3 adhesive joints should be prepared using degreasing solvent and abrasion

  • Place onto tensile testing machine and load until failure

  • Record stress and calculate an average overlap shear strength

  • Review data to check any abnormalities in data, these may suggest poor specimen preparation

 

Surface Preparation:

  • For best performance, part surfaces should be clean and free of grease

  • Steel:

    • Trichloroethylene is a common degreasing agent for steel

  • Carbon fibre:

    • Trichloroethylene is a common degreasing agent for thermoset plastics

    • acetone, or methyl ethyl ketone is an alternative

Research on Trichloroethylene (TCE):

  • Used a solvent for metal degreasing, as a refrigerant, and in dry cleaning fluid

  • TCE poses a human health hazard to the central nervous system, kidney, liver, immune system, reproductive system, and to the developing fetus

  • TCE is characterized as carcinogenic to humans by all routes of exposure (i.e., by inhalation, ingestion, and dermal exposure) by the U.S. Environmental Protection Agency (EPA).

Research on other off-the-shelf degreasing solvents options:

These products lack sufficient technical data sheet to fully validate its compatibility with our material. Its product description suggest that they are usable on a large variety of materials. Any of the options below should be sufficient. It will come down to what products are in-stock during the moment of purchase. Material testing will also be used to investigate the effectiveness and overall necessity of degreasing solvents for adhesive bonding.

 

Note: Learn more about surface preparation here.

 

Material Selection:

  • Technical Data Sheet uses: Steel (grit blasted)

  • We will use any regular steel and it will not be grit blasted due to limited resources.

    • Steel can be found from scrap resources or from E3

 

Potential Improvements to Design if Results Show Insufficient Adhesive Strength:

  • Controlling bond line thickness by using physical limiters such as a jig, or introducing spacer beads into the adhesive mix