Bond failure metal preparation

Cement/metal (CM) failures usually indicate a problem with metal preparation or application of adhesive. They are characterised by the appearance of bare metal in the bonded area of the part. Common causes of CM failure include poor metal preparation, i.e., the presence of contamination on the metal before application of adhesive, insufficient dry film thickness of primer, failure to properly agitate the adhesive to achieve a uniform dispersion prior to application, environmental attack (salt, water) on the primer/metal interface, dry spray of primer on to the metal (which does not allow the primer to... 

Many bonding failures can be traced back to faulty metal preparation, poor application of bonding agents or careless handling techniques on the factory floor. 

Consideration is given to the different steps involved in rubber-to-metal bonding, including surface preparation of metal substrates, the application of primers and adhesives, and moulding, vulcanisation, curing and posttreatment processes. Factors which can lead to weak adhesion and bond failure are discussed, and approaches to the identification and correction of such problems are outlined. 

XPS images recorded from the interfacial failure surfaces of an adhesively bonded aluminum joint, prepared using an organosilane primer, with an instrument of the type shown inO Fig. 9.14. The optical mirror images are complementary views of the fracture surfaces and are mirrored along the dotted line. Visually the failure appears to be interfacial with the fracture path moving from one interface to the other at the boundary between metal and adhesive interfacial failure surfaces... 

The length of the bond between CFRP laminate and the steel joint rings plus steel cylinder is a minimum of 3 in and long enough so that the maximum axial force in the CFRP in the longitudinal direction from aU loading conditions will not cause shear-bond failure or tension failure. The surface of steel substrate over the bond length is prepared to at least near-white-metal condition and is primed to promote adhesion. 

Although distinct "metal" and "adhesive" sides were apparent upon visual examination of the debonded surfaces treated with 100 ppm NTMP, SEM analysis showed the presence of an adhesive layer on the "metal" side. XPS analysis indicated low A1 and 0 and identical high C levels on both debonded sides, confirming a failure within the adhesive layer (cohesive failure), i.e., the best possible performance in a given adherend-adheslve system. This result is similar to that obtained using a 2024 A1 alloy prepared by the phosphoric acid-anodization (PAA) process (16) and indicates the importance of monolayer NTMP coverage for good bond durability (Fig. 4). 

Surface Preparation of the Substrate. This is extremely important for all methods of paint and coatings application. The failure of a paint system is often due not to the paint itself, but because of a failure in surface preparation. For example, an anticorrosive paint applied to a rusty surface will not be effective if the rust falls off taking the new paint with it. For wood and plastic surfaces, old paint or a weathered surface layer may have to be removed. For older metal objects, the removal of corrosion is often required. Sandblasting is one method to remove both the old paint and any corrosion. For new metal objects, a phosphate or chromate layer is often chemically bonded to the metal to provide a surface to which a coating can easily adhere. 

Existence of cyclobutadiene as the simplest cyclic hydrocarbon with conjugated double bonds was predicted by Hiickel in the 1930s. Until recently, however, all attempts to prepare this compound ended in failure. In 1956 Longuet-Higgins deduced 166) that coordination of cyclobutadiene with a transition metal should stabilize its unstable triplet state. 

The failure stress for an equitriaxial extension approximately equals the failure stress for a uniaxial extension, as we see in Table I. (The equitriaxial extension is performed using a thin disk of propellant bonded between two specially prepared plates of metal.)... 

Another tensile test, ASTM D2095-72, involves the testing of bar and rod butt joint specimens. ASTM 2094-69 describes the preparation of these specimens (see Figure 3). This test and the samples can be used with substrates comprised of metals, plastics, or reinforced plastics. Loads are applied through fixtures connected to the samples by dowel pins. The standard test rate is 2400 to 2800 lb per square inch of bond area. The maximum load at failure is used to calculate the tensile strength, the same as for the pi-tensile specimens. 

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