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Abstract The demand for effective de-bondable adhesive technology enabling substrate separation under small loads has grown in recent years. Thermally Expandable Particles (TEP) can be embedded in structural adhesives to promote mechanical separation of the adherends. However, the activation of TEP additives in joints with non-metallic adherends is challenging and can result in substrate thermal damage and poor de-bonding performance, due to the low thermal conductivity and dielectric loss factor typical of plastics and polymer-matrix composites. In this study, the effect of bondline stainless steel inserts on fully composite (Carbon Fiber Reinforced Polymer, or CFRP) bonded Single Lap Joints (SLJ) mechanical and de-bonding performance is evaluated. A centrifugal mixer is used to disperse the TEP in the adhesive. TEP additives are activated using induction heating of the bondline insert, which also helps control crack initiation and propagation. SLJ de-bonding tests are run under a constant 20 lb (89 N) load, and substrate temperature is recorded with thermocouples and an infrared thermometer. Joint strength is evaluated with quasi-static lap shear tests on a servo-hydraulic tensile test apparatus. Preliminary de-bonding testing is performed on a broad initial set of 316 stainless steel insert designs. Out of those, the four best-performing insert geometries are chosen for the complete study. Two TEP enrichment levels (10% and 20% wt.) are investigated. The mechanical and de-bonding performance of SLJs with steel inserts is compared to TEP-only baseline fully-composite and multi-material (AA 6061 Aluminum Alloy + CFRP) joints. The results show that bondline inserts enable fast de-bonding of fully-composite SLJs. Insert geometry and thickness affect joint de-bonding time and reliability, and can be optimized to allow for a partial recovery of lap shear strength. 100% de-bonding reliability is achieved with “block”-type inserts, with de-bonding performance similar to TEP-enriched metallic joints. Visual inspection of the fracture surfaces shows the relationship between TEP activation and crack propagation path. Discussion and conclusions are provided.
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Low‐weight fractions of graphene and hydroxyapatite enhance mechanics in photocured methacrylate adhesives
Abstract In many applications, it is desirable for photocured adhesives to have high‐mechanical strength in the cured state, but relatively low viscosity when liquid. This was achieved by adding less than 0.5 wt% hydroxyapatite and graphene to methyl methacrylate with diurethane dimethacrylate (UDMA‐MMA). Nanoindentation shows hardness increasing by 30–40% and indentation modulus by >30% compared to UDMA‐MMA on its own. Rheometry shows only a small increase in uncured viscosity for the liquid state. The additives affect the optical properties, mobility of free radicals, photocuring, and degree of conversion, the effects of which are seen in Fourier transform infrared and micro‐Raman spectra. Thermographic images taken during curing show that the additives impact the photocuring process. In addition, changes in intermolecular bonding are seen in the vibrational spectra when the additives are present. The enhanced mechanical properties are attributed to the observed changes in photocuring and bonding.
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- Award ID(s):
- 1659099
- PAR ID:
- 10388641
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Applied Polymer Science
- Volume:
- 138
- Issue:
- 20
- ISSN:
- 0021-8995
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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