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Mixed-Mode Bond Fracture Solution

 

VISCA_bond
Adhesives are crucial to modern manufacturing, yet simulating mission-critical structural bonds remains a significant headache. Bondline fracture is complicated by such phenomena as mode-mix, viscoelasticity, and temperature. Psylotech introduces VISCA_bond, an easy to implement, state-of-the-art, adhesive bond simulation solution.

Mixed Mode Fracture Frame
High fidelity cohesive zone modeling must incorporate mode mix. For VISCA_bond, a special dual actuator version of Psylotech’s miniature universal load frame applies any mode mix to a double cantilever beam specimen. (see reverse) Force is measured at each crosshead. Deflection and rotation are measured with DIC (digital image correlation) from speckle patterned “flags” extending from beam ends. Testing protocols and data analysis software are included in adhesive bond simulation solution.

Direct Traction Separation Law Extraction
The Mixed Mode Fracture Frame (MMFF) enables direct extraction of Mode I and Mode II traction separation laws. This key advantage over alternative cohesive zone approaches means the relationship between tractions and displacements is not constrained to any presumed shape. Instead, the nonlinear fracture process zone specific to a given bonding system is directly measured and implemented in FEA.

Workflow
The solution quickly plugs into your existing product design process. First, the adhesive bond system is tested per a standard protocol on the MMFF. Second, a software post processor automatically extracts Mode I & II traction separation laws from experimental data. Third, Abaqus users simply define cohesive zone elements as VISCA_bond elements. The Abaqus workflow is otherwise unchanged.

Rate, Creep & Temperature Dependence
Assuming the polymer adhesive dominates time dependence, Psylotech’s VISCA™ combined with VISCA_bond can model bondline viscoelasticity. VISCA™ is Psylotech’s polymer simulation solution consisting of 1/a contract testing service & 2/an Abaqus material definition add-on module. The software module is a thermodynamics driven, reduced time constitutive model, capable of effectively simulating any strain or temperature history. VISCA™ also includes a viscoelastic bulk modulus, which is important when bond thickness is small relative to the transverse dimensions.

VISCA™ workflow

About Psylotech
Psylotech provides instrumentation to inspire simulation. We produce the µTS, a miniature universal load frame designed for the meso scale. Through high precision and symmetric loading, the µTS imparts negligible out of plane motion, keeping images in focus for effective under microscope DIC. It is compatible with optical, confocal and confocal Raman microscopes as well as SEM and AFM.

 

The µTS is a versatile motion control platform, as realized in the VISCA_bond mixed mode fracture rig. A polymer-specific test system is used for the polymer simulation solution.

Expert Collaboration
The VISCA_bond Mixed Mode Fracture Frame is the evolution of experimental mechanics work done by Prof. Ken Liechti and coworkers over the years. Software to extract traction separation laws as well as the Abaqus user elements also came directly from his group. VISCA_bond is the culmination of his experience plus Psylotech’s premier instrument packaged into an easy to use software tool.

 

Professor Liechti has been studying fracture for over 40 years. He is a Fellow of the ASME, AAM, SEM and AS and an Associate Fellow of AIAA. Select awards include the 2015 Adhesion Society/3M Award for Excellence in Adhesion Science and the 2017 Murray Lecture at the Society for Experimental Mechanics.