Posted by Andrew DeWolfe on Fri, Jul 23, 2010 @ 01:34 PM
There are many test methods used to determine the strength of an adhesive including peel, shear, cleavage, and tension tests. Peel tests are common for tapes, labels, coatings, and other bonded materials. There are three main types of peel tests including 90 degree peel test, 180 degree peel test, and a T-Peel test. The Loop Tack test is similar in concept but is better classified as a tension test.
Why would you perform the T-Peel test instead of the 90 or 180 degree test? Well, the 90 and 180 degree tests are commonly used where a flexible material with an adhesive or other bonding method is adhered to a more rigid substrate. You would use the 90 over the 180 degree peel test if your flexible substrate can't be bent cleanly back to 180 degrees. The T-Peel is used when both materials are either similar or both flexible.
The T-peel test requires that both of the bonded substrates are flexible. This means that they need to be able to be bent up to a 90 degree angle without breaking. Both substrates do not need to be the same material.
Below is a video of the T-Peel test. If you want to see videos of the other peel tests, use these links: 90 degree peel, 180 degree peel, Loop Tack, Package Peel Strength ASTM F88, T-Peel Tissue Adhesives ASTM F2256.
This is a quick summary of the ASTM D1876 specification to decide if this test is right for you, and to point out what equipment you need to perform the test.
Equipment Required:
- Universal Testing Machine
- 1 kN capacity single column UTM is usually enough for this test.
- Servo controlled to keep a constant rate of speed.
- Tensile Grips (2)
- Each peel substrate needs to be held securely
- Software to calculate peak load and average load between extension points
Test Procedure
- Load each end of the sample into opposing tensile grips
- Separate grips at a constant rate of speed (see spec) throughout the length of the specimen (about 9 inches)
- Report peak load and average load per unit width of bond
For reference to ASTM F2256 blog post on T-Peel adhesive bond testing.
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Posted by Andrew DeWolfe on Tue, Jul 13, 2010 @ 12:48 PM
Shear joints impose uniform stresses across the bond area which results in the highest possible joint strength. ASTM D1002 is commonly performed to measure the shear strength of adhesives that are used to bond metals. This test is similar to ASTM D3163 which is for adhesives that bond rigid plastic substrates, and also ASTM D3164 which is for plastic adhesives that are used to bond both plastic and metal substrates. All three of these
specifications use a single lap joint (lap shear) specimen to determine the shear strength of adhesives. If you are going to perform this test, you should read the entire specification from ASTM. This is a quick summary to decide if this test is right for you, and to point out what equipment you need to perform the test. Some of the content in this blog was taken from ADMET's shear testing article in Quality Magazine.
Test Procedure:
- Measure the amount of shear area in square inches or square centimeters.
- Load each end of the specimen in the tensile grips.
- Apply a force at a controlled rate to the specimen until it breaks and record the maximum force and type of joint failure.
- ASTM D1002 specifies a load control rate of 1,200 to 1,400 psi/minute. A cross head control rate of 0.05 inch/minute approximates the loading rate and also is an acceptable mode of control.
Test Report:
- Maximum force
- Maximum shear stress
- Divide the maximum force by the shear area and report
in units of kilogram/square centimeter or psi.
- Type of failure (separation from adhesive to substrate, separation through the adhesive, or both)
Equipment required:
- Universal testing machine (tensile testing machine) with these minimum specifications:
- Servo-controlled to keep a constant rate of speed during the test.
- Breaking load should be between 15 and 85% of machine capacity. This rule may be antiquated as there should be no trouble going to the full scale capacity of a machine. Many strong adhesives require a 10,000 pound (50kN) capacity testing machine (ADMET eXpert 2613). Most common is a 2,000 pound (10kN) testing machine (ADMET eXpert 2611).
- Software or suitable electronics are required to operate the machine, report peak load, and provide a force / displacement chart.
- Grips: Vise grips with serrated inserts are commonly used for lap shear tests. The serrated grip inserts are designed to dig into the material and prevent it from slipping. If slippage occurs with a vice grip, self-tightening grips of pneumatic or wedge design may be used. The grip inserts should be aligned so that the centerline of the grip assembly is aligned with the adhesive bond. Proper alignment is achieved with vice grips by adjusting the grip inserts from side to side so that the center line of the upper and lower grips pass through the adhesive.
Other common adhesive shear specifications:
ASTM D905 - Strength Properties of Adhesive Bonds in Shear by Compression Loading
ASTM D906 - Strength Properties of Adhesives in Plywood Type Construction in Shear
ASTM D1002 - Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens
ASTM D2293 - Creep Properties of Adhesives in Shear by Compression Loading
ASTM D2294 - Standard Guide for Use of Adhesive-Bonded Single Lap-Joint Specimen Test Results
ASTM D2295 - Strength Properties of Adhesives in Shear by Tension Loading at Elevated Temperatures
ASTM D2339 - Strength Properties of Adhesives in Two-Ply Wood Construction in Shear
ASTM D2557 - Tensile-Shear Strength of Adhesives in the Subzero Temperature Range from -267.8 to -55 C
ASTM D2919 - Determining Durability of Adhesive Joints Stressed in Shear by Tension Loading
ASTM D3163 - Determining Strength of Adhesively Bonded Rigid Plastic Lap-Shear Joints in Shear
ASTM D3164 - Strength Properties of Adhesively Bonded Plastic Lap-Shear Sandwich Joints in Shear
ASTM D3165 - Strength Properties of Adhesives in Shear Single-Lap-Joint Laminated Assemblies
ASTM D3166 - Fatigue Properties of Adhesives in Shear by Tension Loading (Metal/Metal)
ASTM D3528 - Strength Properties of Double Lap Shear Adhesive Joints by Tension Loading
ASTM D3931 - Determining Strength of Gap-Filling Adhesive Bonds in Shear by Compression
ASTM D4027 - Measuring Shear Properties of Structural Adhesives by the Modified-Rail Test
ASTM D4498 - Heat-Fail Temperature in Shear of Hot Melt Adhesives
ASTM D4501 - Shear Strength of Adhesive Bonds Between Rigid Substrates by the Block-Shear Method
ASTM D4562 - Shear Strength of Adhesives Using Pin-and-Collar Specimen
ASTM D5656 - Thick-Adhered Metal Lap-Shear Joints for the Stress-Strain Behavior
ASTM D5868 - Lap Shear Adhesion for Fiber Reinforced Plastic (FRP) Bonding
ASTM D6463 - Time to Failure of Pressure Sensitive Articles under Sustained Shear Loading
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Posted by Andrew DeWolfe on Fri, Jun 04, 2010 @ 08:06 AM
One method to measure the tack force / strength of an adhesive is to perform the "Loop Tack" test method described in specification ASTM D6195. The adhesives tested with this test are typically pressure sensitive adhesives (PSA) applied to films, labels, tapes, and stickers where the initial tack force is an important characteristic of the product. The specification describes two ways to perform the test. One method (Method B) uses a single purpose machine. Although the simplicity of one dedicated machine is nice, the loop tack method is uncommonly the sole test of any manufacturer. The other method (Method A) uses a universal testing machine otherwise known as a tensile testing machine. Using this method provides you with accurate test results, the same ease of use as the single purpose machine, and also allows you to use the universal testing machine for many other common adhesive and material tests such as 90 degree peel adhesion tests, 180 degree peel adhesion tests, and standard tensile strength testing. If you only need to perform the loop tack test you should consider a single purpose machine and follow Method B. If you have a tensile testing machine, or need to perform other adhesive and material tests, you should follow Method A.
This is a short video of the test followed by a simple summary to help determine if this test is right for your application. Please read the entire ASTM specification if you decide to perform the test.
Procedure:
1. Make a loop with your tape with the adhesive on the outside of the loop.
2. Place the loop in the top grip of the universal testing machine.
3. Bring the loop into contact with a 1" cube fastened to the bottom of the universal testing machine.
4. Remove the tape from the 1" cube fixture.
5. Report the peak and/or the average force during removal.
Test performed on an ADMET eXpert 7601 universal testing machine.
Test report generated from ADMET's MTESTQuattro testing software.
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