| Epoxy | Usually two-part; working and cure times range from minutes to hours depending on formulation and temperature. Some grades require heat to reach their specified properties. | Often high strength and stiffness, with good gap-filling options. Toughened formulations can improve impact resistance. | Metals, ceramics, glass, and prepared composite surfaces. | Rigid grades may be vulnerable to peel, impact, or differential thermal movement. Surface preparation and mix ratio are important. | Lap shear (ASTM D1002 or ISO 4587); peel where relevant (ASTM D903); environmental aging followed by strength testing. |
| Polyurethane (PU) | Available as one-part moisture-curing or two-part systems. Handling and full-cure times vary; thick sections may cure more slowly. | Generally more flexible and impact tolerant than rigid epoxies; can accommodate some movement. Strength varies widely by grade. | Wood, metals, many plastics, and composites, subject to substrate and formulation compatibility. | Moisture, temperature, and substrate chemistry can affect cure and adhesion. Some grades need primers or controlled bond-line thickness. | Lap shear; peel or cleavage testing for flexible joints; water or humidity aging followed by bond testing. |
| Methyl methacrylate (MMA) acrylic | Commonly two-part and relatively fast-curing. Open time, fixture time, and heat generation depend on formulation and joint size. | Often combines high bond strength with better impact tolerance than brittle, unmodified systems; some grades bond with limited surface preparation. | Metals, composites, and selected plastics, including some difficult-to-bond thermoplastics when the formulation is suitable. | Odor, exotherm, gap limits, and compatibility with plastics should be assessed. Confirm the adhesive will not stress-crack the substrate. | Lap shear on the actual substrate pair; peel or impact testing for the joint design; check for substrate damage and cure heat. |
| Silicone | Often one-part, moisture-curing RTV; skin formation may occur before full cure. Cure can take longer in thick or enclosed joints. | Highly flexible and suited to sealing or joints exposed to movement and weather. Usually selected for flexibility rather than maximum structural load. | Glass, ceramics, and some metals or plastics, depending on grade and surface treatment. | Adhesion can be substrate-specific; some formulations need primer. Verify compatibility with paints, coatings, and nearby materials. | Peel or adhesion checks on prepared coupons; movement cycling; heat, humidity, or weather exposure appropriate to service conditions. |
| Cyanoacrylate | Usually one-part and fast-setting when thin films contact suitable surfaces. Fixture can occur quickly, while full property development takes longer. | Effective for small, close-fitting joints; many grades form relatively rigid bonds. Specialized grades may improve flexibility or performance on particular substrates. | Some metals, elastomers, and plastics; actual compatibility depends strongly on the material and adhesive grade. | Typically poor for large gaps and prolonged peel or impact loading. Surface moisture, acidic surfaces, and some plastics can affect cure or adhesion. | Lap shear on the actual materials; bond-line and gap trials; aging tests at the expected temperature and humidity. |
| Project-specific test plan | Test the proposed application process, including mixing, dispensing, open time, clamping, and cure conditions. | Evaluate the complete joint, not just a material’s advertised strength. Record failure mode as well as peak load. | Use production-representative substrates, coatings, surface preparation, and bond-line thickness. | Test the real service environment: temperature, moisture, chemicals, vibration, load direction, and expected joint movement. | Use ASTM D1002 or ISO 4587 for metal lap-shear comparisons; ASTM D903 for peel testing of suitable flexible joints. Select the method and specimen geometry to match the application. |