How to Perform a 3 Point Bend Test on a Universal Testing Machine

Bend testing (also flex or flexural testing) is commonly performed to measure the flexural strength and modulus of all types of materials and products.  This test is performed on a universal testing machine (tensile testing machine or tensile tester) with a 3 point or 4 point bend fixture.  Most common for product testing is the 3 point test.

 

 

The key analysis when performing bend testing are:

1. Flexural Modulus - This measures the slope of a stress / strain curve and is an indication of a material's stiffness
2. Flexural Strength - This measures the maximum force that a material with withstand before it breaks or yields.  Yield is where you have pushed a material past its recoverable deformation and it will no longer go back to the shape it once was.
3. Yield Point - The yield point is the point where the material essentially "gives up" or the point where if you were to continue to bend the product, the force will not continue to increase and will then start to decrease or break.

The video below shows a bend test.  The actual part is a pen, but the same test can be run on nearly any product or material.  As you can see from the video, there is a point during the test where the bent area of the red pen turns white.  This happens to occur around the same time as the yield point.  

Test Report from ADMET's MTESTQuattro Testing Software:

How to Perform an ASTM D638 Plastic Tensile Strength Test

ASTM D638 ( D 638 ) is one of the most common plastic strength specifications and covers the tensile properties of unreinforced and reinforced plastics.  This test method uses standard "dumbell" or "dogbone" shaped specimens under 14mm of thickness.  A universal testing machine (tensile testing machine) is needed to perform this test.  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.

First off, do not perform this test if you have films or elastomers.  If you have film under 1mm in thickness use ASTM D882.  If you have an elastomer use ASTM D412.

Test Procedure:

1. Cut or injection mold your material into one of the five "dumbbell" shapes.  The exact shape you use is dependent upon your material's rigidity and thickness.
2. Load the specimen into tensile grips.
3. Attach the extensometer to the sample
4. Begin the test by separating the tensile grips at a constant rate of speed.  Speed depends on specimen shape and can range from 0.05 - 20 inches per minute.  The target time from start of test to break should be from 30 seconds to 5 minutes.
5. End the test after sample break (rupture)

Analysis obtained: 

1. Tensile Strength
2. Percent Elongation at Yield
3. Percent Elongation at Break
4. Nominal Strain at Break (Grip Separation)
5. Modulus of Elasticity
6. Secant Modulus
7. Poisson's Ratio (Requires Transverse Extensometer)

Equipment required:

1. Universal testing machine (tensile testing machine)
   
   1. Needs to be servo controlled to keep a constant rate of speed.
   2. Capacity needs to be enough for your materials.  Usually a low force 2,000 pound dual column machine is enough for most common materials.  A high capacity 10,000 pound (or more) model is required for larger samples and/or stronger materials such as reinforced plastics or composites.
2. Extensometer
   1. Required when measuring modulus, yield, and modulus. Why?  For two reasons: 1) The linear region of plastics is very small and happens suddenly so grip separation is just not accurate enough.  2) Dumbbell specimens do not have uniform widths so there will be errors when both the wide and narrow sections of the dumbbell shaped specimen elongate at different rates. 
3. Data Acquisition
   1. Software or suitable electronics are required to operate the machine and to take the measurements. Basic systems will provide the raw data, and stress-strain charts. Using these sources of data, you can determine and calculate all of the analysis listed above. However, fully PC based systems have the capability to calculate all of these automatically. For example, our MTESTQuattro testing software has built in support for ASTM D638 and all of these calculations are provided immediately after performing the test.
4. Tensile Grips
   
   1. Any grip with serrated faces is usually adequate for this test.  You can use wedge, pneumatic, vise, or other self tightening grips such as eccentric roller or scissor grips.

Outdoor Gear Buckle and Webbing Breaking Strength Tensile Test

The outdoor apparel and gear industry is a very frequent user of universal testing machines (UTM's). Universal testing machines can be programmed to perform a variety of tension (pull apart), compression (crush), and flexure (bend) tests. Strength and stretch are important design criteria for outdoor and athletic products. It may not be extremely important that a soda bottle withstand a large compressive load but it certainly is important if a rock climbing harness doesn't break.

This is a test of a side release buckle used to connect a lashing strap. As you can see in the video, this buckle would be fine for lashing a sleeping pad on a backpack, but you certainly would not want to use it for climbing.

The machine in the video is a standard ADMET dual column eXpert 2600 series universal testing machine. It has 16" of space between the columns which satisfies most users. However, some need wider machines to test larger products such as this 26" diameter mountain bike tire:

The following are a few examples of outdoor products that require testing and can be easily tested on a universal testing machine:

1. Tested in Tension (pull apart)
1. Climbing rope and caribiners
2. Dog Leashes and Harnesses
3. Zipper Pulls
4. Seam strength of clothes, parkas, tents, backpacks, etc.
5. Lashing Straps
2. Tested in Compression (crush)
1. Bike Frames and wheels
2. Shoe soles
3. Tested in flexure (bend)
1. Skis and Snowboards
2. Tent poles

Hook and loop fastener strength test on a universal testing machine

Hook and loop (often times referred to by the trade name Velcro) fasteners are commonly tested through both a Peel Strength "T" Method (ASTM D5170) and Shear Strength Dynamic Method (ASTM D5169).  Hook and loop fasteners are also used in applications where separation occurs purely in the tension direction.  This video shows a test where an adhesive backed hook and loop fastener is adhered to a pair of compression platens mounted to a universal testing machine (tensile testing machine).  The test has been designed so that in one test the hook and loop is loaded to 1 pound of force and then retracted to measure the bonding strength.  It then continues to load to 10 pounds of force, then retract, then load to 20 pounds, then retract, and so on until 80 pounds of force.  After the test is completed, the strength can be measured by analyzing the test report with load on the "Y" axis and time on the "X" axis.

 

This test was performed on an ADMET eXpert 7601 universal testing machine equipped with the most advanced materials testing software, MTESTQuattro.  For more information on this or any other ADMET testing system please visit www.ADMET.com

 

 

 

 

 

 

 

 

 

 

 

How to Perform an ASTM C469 Concrete Compression Test

How to Perform an ASTM D412 Rubber Elastomer Tensile Strength Test

ASTM D412 ( D 412 ) covers the tensile properties of thermoset rubbers and thermoplastic elastomers. The specification describes two test methods, A and B. Method A is common and can be performed on a universal testing machine (tensile testing machine). 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.

This video shows the basic steps necessary to perform the ASTM D412 test:

 

Test Procedure:

1. Cut or injection mold your material into a "dumbbell" shaped specimen. 

2. Load the specimen into tensile grips.
3. Attach the optional extensometer to the sample
4. Begin the test by separating the tensile grips at a speed of 20 inches per minute
5. End the test after sample break (rupture)

Analysis obtained:
1. Stress at user-specified extension or elongation
2. Tensile Yield Stress
3. Tensile Yield Strain
4. Tensile Strength at Rupture
5. Elongation at Rupture

Equipment required:

1. Universal testing machine (tensile testing machine) with these minimum specifications:
A. Servo-controlled to keep a constant rate of speed during the test (+/- 2 inches/min)
B. At least 30 inches of crosshead travel or more for high elongation materials
C. Most small and common 1kN (225 pound) load capacity machines will work for the loads of the materials tested to this specification

All of our eXpert 2600 series dual column machines meet these requirements, and it is also common to use our single column eXpert 7601 XLT with 53 inches of crosshead travel.

2. An extensometer is optional but recommended. We recommend one for two reasons. First, dumbbell specimens do not have uniform widths which cause errors when both the wide and narrow sections of the dumbbell shaped specimen elongate at different rates. Secondly, elongation is usually an important design characteristic of rubbers and elastomers so an extensometer can be used to improve accuracy of the measurement.

3. Software or suitable electronics are required to operate the machine and to take the measurements. Basic systems will provide the raw data, and stress-strain charts. Using these sources of data, you can determine and calculate all of the analysis listed above. However, fully PC based systems have the capability to calculate all of these automatically. For example, our MTESTQuattro testing software has built in support for ASTM D412 and all of these calculations are provided immediately after performing the test.

4. Tensile grips hold your specimen during the test as it is being pulled apart. Quite often, hard specimens are difficult to hold properly as premature breakage and slippage can be common. However, rubbers and elastomers usually lend themselves to being easily held in a variety of grip designs such as manual vise grips, pneumatic grips, wedge grips, or eccentric roller designs. The most common and easy to use grips are manual vise or pneumatic grips with rubber coated or serrated insert faces.

Click here for a quote for our 1kN, 2.5kN, or 5kN eXpert 7600 machine equipped to perform the ASTM D412 test.  Or click here if you need a larger dual column machine.

 This is a new version of this earlier post. 

 

90 Degree Adhesive Peel Strength Test on a Universal Testing Machine

This video shows a 90 degree adhesive peel strength test on an ADMET eXpert 7601 universal testing machine (tensile testing machine).  We fit the eXpert 7601 with our 90 degree peel strength fixture and one vise grip on the top crosshead to hold the free end of the tape.  The fixture has numerous tapped holes that allow you to clamp a multitude of various parts and substrates to the test bed.  This test measures the maximum load and also the average load of adhesive tape bonded to a Polystyrene foam substrate.  The average was taken after 1" of displacement and continued through 6" of displacement.  Usually, the highest force is observed at the beginning of a peel test and then it levels out throughout the remainder of the test.  Starting the average force calculation after 1" removed the "starting force" from the average calculation.

 

   

 

Rubber Seal Compression Testing to Obtain Load vs. Deflection Curve

Torsion Fatigue Tester for Medical Device Testing

ADMET offers electromechanical and servo-hydraulic fatigue testing systems for tension, compression, torsion and biaxial testing applications.  All systems are engineered to meet your needs (The eXpert 81T 30Nm Torsion Fatigue Tester shown in the video is for medical device testing.).

ADMET equips each fatigue tester with a high-speed closed-loop multi-channel controller called MTESTQuattro(R) Dynamic. MTESTQuattro(R) will produce sine, square and triangular waveforms based on force, displacement, torque or angle amplitude control. Users can manually adjust control gains and end point values on the fly or activate amplitude control so that the controller automatically adjusts the end point values to ensure waveform amplitudes stay within tolerance. Biaxial systems employ two axis of control which can be programmed to operate independently or in unison.

Suture tensile strength test