ASTM D950 Test Method for Impact Strength of Adhesive Bonds

Get Certified ASTM D950 Testing for Reliable Adhesive Impact Performance

In applications that require high strength, adhesive bond strength is directly related to structural performance and safety. ASTM D950 certification ensures adhesives perform as required in automotive, aerospace, and building applications. A good laboratory test can give repeatable and reliable information for selecting adhesives, quality control, and material evaluation. This testing aids in product development and assists manufacturers in testing the performance of their adhesives in shock-loaded structures.

The scope of ASTM D950 includes:

• Material type: ASTM D950 applies to metal-to-metal and wood-to-wood bonding, such as brass, copper, aluminum, steel, phosphor bronze, magnesium, nickel silver, and hard maple wood. 
• Purpose: ASTM D950 measures the ability of various adhesives to withstand suddenly applied loads and compares the impact strength of adhesive bonds. 
• Property measured: The test measures impact strength in joules per square meter (J/m²) or foot-pound force per square inch (ft·lbf/in²). 
• Method: The impact velocity is 3.4 m/s (11 ft/s), and the method is a pendulum-type impact machine (ASTM D950) that impacts the specimen at the bond line.
• Result: The testing laboratory obtains impact strength values from the specimens it tests. 
• Test Limitations: The test method is comparative and is not intended to provide design allowable stresses for structural joints.
• Environmental conditions: The test program is based on conditioning at 50 ± 2% RH and 23 ± 1.1 °C (73.4 ± 2 °F).
• Applications: Adhesive selection for bonded assemblies in the construction, automotive, and aerospace industries for shock loading, drop, and high-rate loading applications. 

What are the Uses of ASTM D950 Testing?

ASTM D950 testing helps laboratories provide valid impact strength data for adhesive quality evaluation. These results are important for adhesive selection, quality control, and product development by manufacturers and engineers. This standard-

• The comparison of the impact resistance of various adhesive systems.
• Testing adhesion in fast loading situations
• Materials and methods for structural bonding in automotive applications
• Electronics assembly drop shock resistance support test work
• Evaluating adhesives for aerospace structures that experience impact loads
• Characterizing construction adhesives for high vibration environments. 

Which materials can be tested under ASTM D950?

ASTM D950 is for bonding between metal and metal or wood and wood. Brass, copper, aluminum, steel, phosphor bronze, magnesium, nickel silver, and other metals referenced in ASTM specifications are considered metal specimens. Wood-to-wood specimens use hard maple wood. The test method can assess epoxies, polyurethanes, acrylics, and cyanoacrylate-based adhesives under impact loading conditions. 

Why is ASTM D950 Important?

ASTM D950 is a standard for measuring the impact strength of adhesive bonds. Adhesives can fail under sudden impact loads and not under slowly applied loads of the same or greater force. This is why impact testing is critical for applications that are subject to shock loads, drops, vibrations, or high-rate loading events. The test method helps manufacturers choose the right adhesive for high-stress applications and maintain structural integrity in the automotive, aerospace, and construction industries. 

ASTM D950 Testing Process and Data Collection

The testing process starts by bonding the adherend blocks with the test adhesive. Technicians condition the specimens at 50 ± 2 % relative humidity and 23 ± 1.1 °C (73.4 ± 2 °F). The specimen is mounted in a steel jig attached to the base of the impact machine, and the retaining screw is tightened. The height of the impact head is set and then allowed to fall to strike the specimen at the bond line. The testing machine quantifies the amount of energy absorbed when failure occurs. To measure impact strength, the analyst determines the amount of energy absorbed over the bonded area and documents the results to compare materials.

Common Challenges and Troubleshooting in ASTM D950

Accurate ASTM D950 results depend on proper specimen preparation and correct equipment calibration. Strength test results are only as accurate as the adhesive manufacturer-supplied bonding process conditions. Typical problems include bondline thickness variation, curing problems, and specimen misalignment. Technicians need to follow the manufacturer’s guidelines for surface preparation, adhesive preparation, application, assembly, and curing. The reliability of the data obtained in the laboratory is dependent on the proper conditioning of the specimens, routine calibration of the impact machine in accordance with Test Method E23, and trained technicians performing the test in a consistent manner. 

• The energy absorbed by the specimen for any given bonded area is reported as the impact strength in joules per square meter (J/m²) or foot-pound force per square inch (ft·lbf/in²) in the laboratory.
• Analysts record the energy the specimen absorbs on failure from a single blow of the failure-testing machine hammer.
• Failure mode classification: Failure mode is identified as adhesive, cohesive, or adherend failure.
• To ensure statistical reliability, the laboratory reports the mean, minimum, and standard deviation of impact strength values.
• The impact strength test results are compared to the applicable requirements, and the conformity of the tested adhesive to the specification is indicated.
• Manufacturers guarantee that their adhesives comply with the impact strength requirements specified in ASTM D950. Accredited laboratories conduct compliance testing to ensure adhesives meet the specific requirements.

Link to ASTM D950