Search Results for Clevis

The fracture of a clevis which formed part of the derricking gear of a large crane showed well developed conchoidal markings. These were associated with a principal origin on the outer surface at about the mid-width of the section. A number of secondary origins were apparent along this same edge. Failure was initiated at the extrados which suggested that a discrepancy in the size of the pin may have contributed to failure. Microscopic examination of a section through the main origin did not reveal any material defects or the presence of weld repairs which could have led to the premature failure. Furthermore, there were no indications that corrosion had contributed to the fatigue cracking.

A hi-rail device is a vehicle designed to travel both on roads and on rails. In this case, a truck was modified to accept the wheels for rail locomotion. The rear wheel/axle set was attached to the truck frame. Both the front and rear wheel/axle sets were raised by means of a hydraulic cylinder driven off the PTO of the truck. The wheel/axle set was rigidly fixed into an up or down position by the use of locking pins. It was assumed by the manufacturer that there would be no load on the cylinder once the wheel/axle set was in its locked position. However, as the cylinder pivoted about its mounting trunnion and extended during its motion, it interfered with a frame member. This caused both a bending load and a rotational movement. These effects caused a combination of fretting, galling, and fatigue to the internal thread structure of the clevis. As a result of these deleterious effects, failure of the thread structure of the clevis occurred. The failure occurred where the cylinder rod screws into the clevis. The rod was manufactured from 1045 steel.

Two 38 mm (1.5 in.) diam threaded stud bolts that were part of a steel mold die assembly from a plastics molding operation were examined to determine their serviceability. Chemical analysis showed the material to be a plain carbon steel that approximated 1045. Visual examination revealed evidence of severe hammer blows to the clevis and boss areas and a gap between the die and the underside of the boss. Magnetic particle inspection showed cracks at the thread roots that, when examined metallographically, were found to contain MnS stringers. The cracking of the threads was attributed to a poor stud bolt design, which allowed a high stress concentration to occur at the base of the threads upon application of a lateral load. It was recommended that bolts of a new design that incorporated a stress-relieving groove be used. Threading of the bolt to eliminate the gap between the lower face of the boss and the die and an improved method of inserting or removing the bolt to avoid hammering (use of a wrench on a square or hexagonal boss) were also recommended.

Two clevis-head self-retaining bolts used in the throttle-control linkage of a naval aircraft failed on the aircraft assembly line. Specifications required the bolts to be heat treated to a hardness of 39 to 45 HRC, followed by cleaning, cadmium electroplating, and baking to minimize hydrogen embrittlement. The bolts broke at the junction of the head and shank. The nuts were, theoretically, installed fingertight. The failure was attributed to hydrogen embrittlement that had not been satisfactorily alleviated by subsequent baking. The presence of burrs on the threads prevented assembly to finger-tightness, and the consequent wrench torquing caused the actual fractures. The very small radius of the fillet between the bolt head and the shank undoubtedly accentuated the embrittling effect of the hydrogen. To prevent reoccurrence, the cleaning and cadmium-plating procedures were stipulated to be low-hydrogen in nature, and an adequate post plating baking treatment at 205 deg C (400 deg F), in conformity with ASTM B 242, was specified. A minimum radius for the head-to-shank fillet was specified at 0.25 mm (0.010 in.). All threads were required to be free of burrs. A 10-day sustained-load test was specified for a sample quantity of bolts from each lot.

A sand-cast steel eye connector used to link together two 54,430 kg capacity floating-bridge pontoons failed prematurely in service. The pontoons were coupled by upper and lower eye and clevis connectors that were pinned together. The eye connector was found to be cast from low-alloy steel conforming to ASTM A 148, grade 150-125. The crack was found to have originated along the lower surface initially penetrating a region of shrinkage porosity. It was observed that cracking then propagated in tension through sound metal and terminated in a shear lip at the top of the eye. The fracture of the eye connector was concluded to have occurred by tensile overload because of shrinkage porosity. Sound metal was ensured by radiographic examination of subsequent castings.

Cracks were discovered in the cast 17-4 PH stainless steel outboard leading edge flap support of an aircraft wing during overhaul inspection. Failure analysis focused on an apparently intergranular area of fracture surface. It was determined that the original mode of crack growth was cleavage, probably caused by cast-in hydrogen. The intergranular appearance resulted from heat treatment of the already cracked part, which caused the formation of grain-boundary “growth figures” on the exposed crack surfaces. It was recommended that the castings be more closely inspected for defects before further processing and that foundry practices be reviewed to correct deficiencies leading to excessive hydrogen absorption during melting and casting.

This article describes the underlying fundamentals, applications, the relevance and necessity of performing proper stress analysis in conducting a failure analysis. It presents an introduction to the stress analysis of bodies containing crack-like imperfections and the topic of fracture mechanics. The fracture mechanics approach is an important part of stress analysis at the tips of sharp cracks or discontinuities. The article reviews fracture mechanics concepts, including linear elastic fracture mechanics, elastic-plastic fracture mechanics, and subcritical fracture mechanics. It also provides information on the applications of fracture mechanics in failure analysis.

This article describes concepts and tools that can be used by the failure analyst to understand and address deformation, cracking, or fracture after a stress-related failure has occurred. Issues related to the determination and use of stress are detailed. Stress is defined, and a procedure to deal with stress by determining maximum values through stress transformation is described. The article provides the stress analysis equations of typical component geometries and discusses some of the implications of the stress analysis relative to failure in components. It focuses on linear elastic fracture mechanics analysis, with some mention of elastic-plastic fracture mechanics analysis. The article describes the probabilistic aspects of fatigue and fracture. Information on crack-growth simulation of the material is also provided.

This article discusses different types of mechanical fasteners, including threaded fasteners, rivets, blind fasteners, pin fasteners, special-purpose fasteners, and fasteners used with composite materials. It describes the origins and causes of fastener failures and with illustrative examples. Fatigue fracture in threaded fasteners and fretting in bolted machine parts are also discussed. The article provides a description of the different types of corrosion, such as atmospheric corrosion and liquid-immersion corrosion, in threaded fasteners. It also provides information on stress-corrosion cracking, hydrogen embrittlement, and liquid-metal embrittlement of bolts and nuts. The article explains the most commonly used protective metal coatings for ferrous metal fasteners. Zinc, cadmium, and aluminum are commonly used for such coatings. The article also illustrates the performance of the fasteners at elevated temperatures and concludes with a discussion on fastener failures in composites.

This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.

This article focuses on the general root causes of failure attributed to the casting process, casting material, and design with examples. The casting processes discussed include gravity die casting, pressure die casting, semisolid casting, squeeze casting, and centrifugal casting. Cast iron, gray cast iron, malleable irons, ductile iron, low-alloy steel castings, austenitic steels, corrosion-resistant castings, and cast aluminum alloys are the materials discussed. The article describes the general types of discontinuities or imperfections for traditional casting with sand molds. It presents the international classification of common casting defects in a tabular form.