WHY USE ARCH MATERIAL SERVICES

Arch Material Services has developed a machining process to eliminate the potentially detrimental effects of typical fabrication processes. Lap Shear adherends are most often produced using die cut, water jet, laser or shearing methods resulting in adherends with compressed edges, jagged edges, residual stress, loss of temper and may be physically twisted or bent.

Typical adherend fabrication processes create heat or (compressive) loads along the edges that can alter the mechanical properties created by the heat-treat (temper) process. The altered property (reduced strength on edges) is significant thus creating inherent stress within the metal. The chart below illustrates strength levels between two common tempers for 2024 aluminum.

Since bond edges have the highest stress concentration under load, and if the adherend edges are compromised they may create a gateway to initiate bending of adherends, commonly seen as rotation under load. Illustrated here:

Rotation under load as shown above creates a multi-mode failure, increasing peel while decreasing shear. Since the test is focused on shear properties, rotation can yield non-representative test results. Properly machined adherends retain their mechanical properties paving the way for reduced rotation under load. Giving you the best opportunity for proper test results of your adhesive while also reducing variability.

Our process preserves the original temper and properties throughout the machined adherend. At the same time allows for precision machining for exceptional dimensional control.

Why

Making superior and eco friendly products are possible with focused effort and rethinking the end to end process. And we can do all this and create much higher value for our customers. Please give Arch Materials Services products a try.

ARCH DIFFERENCE

U.S. SOURCED ALLOYS

CERTIFIED TO ASTM B209

EXTREMELY FLAT TO WITHIN 0.0005" PER INCH

MACHINED TO EXACTING TOLERANCE

PRECISE SMOOTH EDGES

PROCESSED WHILE PRESERVING METAL TEMPER

STRESS FREE PANEL

WHY SLOTTED

It is helpful to understand the entire process to appreciate the advantage of slotted plates for lap shear testing.

Prevent detrimental specimen damage - Slotted panels, after curing can go directly into testing. Flat bonded panels must be cut into specimens.

The sawing/machining process can cause detrimental micro cracking of bond from vibration, generate excessive heat or introduce water if wet cut.

Better bond line thickness control - Accurate adhesive shear results are partly dependent on the bond line thickness. Slotted specimen panel bonding allows for relief of excess adhesive on 4 sides of each specimen.

Flat bonded panels tend to crown in the middle of continuous bond areas, resulting in slightly uneven bond line thickness.

Speed to test - Once panels are bonded, slotted panels can be tested immediately after any environmental conditioning. Flat bonded panels will require cutting and machining prior to conditioning and test.

Better process efficiency - Slotted panels can be fabricated quickly and efficiently compared to flat bonded panels. With slotted panels, specimens may be simply broken apart to test. Flat bonded panels will require considerable manual handling as well as equipment to cut and machine into specimens. The high labor per part of flat bonded specimens not only adds cost but more opportunity for error and variability.

Minimize environment impact with slotted panels - Slotted panels create the specimen geometry before bonding and all scrap generated up to that point can easily be recycled. Alternatively, machining specimens after bonding, the scrap materials (mix of metal and adhesive) would be difficult to recycle and likely end up as landfill.

THE INFLUENCE OF RESIDUAL STRESS

IN ADHESIVE SHEAR TESTING

Intuitively a small amount of residual stress in adherends like aluminum is significant compared to adhesive properties. In reality it is difficult to assess what if any impact substrate residual stress has on adhesive shear, peel or crack growth properties.

Often in practice after a lap shear test is completed, the adherends appear to be out-of-plane to each other, giving concern that the metals are relieved of stress that was inherent in the bonded specimen.

To prevent residual stress, Arch Material Services uses a balanced machining process on aluminum adherends. Careful consideration is given to the machining process and execution to prevent stress risers, thermal damage or emparting stress into adherends.

Minimizing variables in lap shear testing starts with eliminating the residual stress of adherends and test specimens. Slotted lap shear and other adherend panels by Arch Material Services provide your best opportunity to capture your true shear, peel or tensile adhesive properties.