Initiation of failure

J. Gough and A.H. Muhr, Initiation of failure of rubber close to bondlines, in Proceedings of International Rubber Conference, Maastricht, The Netherlands, June 2005, lOM Communications Ltd., London, 2005, pp. 165-174. 

The impHcation of this result is that pure triblock systems wiU perform best in PSA appHcations where initiation of failure is the Hmiting factor, such as long-term resistance to shear. However, for applications where a specific peel force is required, it is not clear that the pure SIS formulations will perform better since the maximum fibril extension is systematically reduced for the triblock based adhesives relative to the adhesives containing diblocks. 

The masses involved in a slide or slump behave in a variety of ways after the initiation of failure. The soil mass behavior may range from slow creep movements, to rapid debris flows, and dilute turbidity currents. Middleton and Hampton (1976) have discussed the evolution of different t) es of flows, and have suggested a classification based on concentration and time and/or space. These various types of flow slides are given in the following list arranged from low to high concentration of particles ... 

Another failure mode for a material under mechanical load is the plastic strain. The stress concentration at the tip of a crack increases the probability that dislocations will nucleate and move at the head of the crack tip. However, unlike in brittle fracture, plasticity dissipates a lot of energy, thus reducing the stress concentration by blunting the crack. This type of ductile behavior, typical in metals, leads to robust structural materials the initiation of failure does not necessarily extend catastrophically through the entire specimen, and a lot of energy is dissipated during the process of the material strain. 

Eakins, W. J. (1966), Initiation of Failure Mechanisms in Glass-Resin Composites, NASA Report CR-518, August 1966. 

Identify those tasks that are most critical from a risk point of view, either through initiation of failures (initiating events) or failures of important barrier functions. 

Chan and Vedhagiri (2001) studied the response of various configurations of single-lap joints, namely bonded, bolted, and bonded-bolted joints by three-dimensional FE method and the results were validated experimentally. The authors found that for the bonded-bolted joints, the bolts help to reduce the stresses at the edge of the overlap, especially after the initiation of failure. The same type of study was carried out by Lin and Jen (1999). 

Figure 4.3 shows creep failure curves for PVC. The upper curve is for ductile failure due to necking, normally identified as the start of creep rupture. The dashed line indicates the initiation of crazing. In order to prevent the initiation of failure the strain must be kept below 0.010. 

If a rock is sufficiently stressed, the yield point will eventually be reached. If a brittle failure is initiated a plane of failure will develop which we describe as a fault. Figure 5.6 shows the terminology used to describe normal, reverse and wrench faults. 

The failure rate changes over the lifetime of a population of devices. An example of a failure-rate vs product-life curve is shown in Figure 9 where only three basic causes of failure are present. The quaUty-, stress-, and wearout-related failure rates sum to produce the overall failure rate over product life. The initial decreasing failure rate is termed infant mortaUty and is due to the early failure of substandard products. Latent material defects, poor assembly methods, and poor quaUty control can contribute to an initial high failure rate. A short period of in-plant product testing, termed bum-in, is used by manufacturers to eliminate these early failures from the consumer market. 

A failure that occurs while an independent device is awaiting repair represents but one failure during the time frame of the initiation of the emergency and is therefore credible. The lack of availability of the unrepaired device is a preexisting condition. 

SCC has been defined as failure by cracking under the combined action of corrosion and stress (Fig. 9.1). The stress and corrosion components interact S3mergistically to produce cracks, which initiate on the surface exposed to the corrodent and propagate in response to the stress state. They may run in any direction but are always perpendicular to the principal stress. Longitudinal or transverse crack orientations in tubes are common (Figs. 9.2 and 9.3). Occasionally, both longitudinal and transverse cracks are present on the same tube (Fig. 9.4). Less frequently, SCC is a secondary result of another primary corrosion mode. In such cases, the cracking, rather than the primary corrosion, may be the actual cause of failure (Fig. 9.5). 

Heavy equipment had passed over the site of failure initiation shortly before the rupture was discovered. It is probable that stresses associated with the heavy equipment initiated a fracture in the severely corroded pipe bottom. Once the fracture initiated, it propagated down the length of the line in response to stresses imposed by internal pressure. 

Eail-Safe Design features which provide for the maintenance of safe operating conditions in the event of a malfunction of control devices or an interruption of an energy source (e.g., direction of failure of a control valve on loss of signal). A system is fail-safe if failure of a component, signal, or utility that would create a hazard initiates an action that maintains the system in a safe condition. 

The effeet of failure eost or quality loss on the profitability of a produet development projeet is shown in Figure 1.1. High levels of failure eost would produee a loss on sales and would probably mean that the projeet fails to reeover its initial level of investment. 

Measures to minimize safety problems must be initiated at the start of the life cycle of any product, but too often determinations of criticality are left to production or quality control personnel who may have an incomplete knowledge of which items are safety critical (Hammer, 1980). Any potential non-conformity that occurs with a severity sufficient to cause a product or service not to satisfy intended normal or reasonably foreseeable usage requirements is termed a defect (Kutz, 1986). The optimum defect level will vary according to the application, where the more severe the consequences of failure the higher the quality of conformance needs to be. 

Comparing this value with the initial design s high potential eost of failure, it is evident that a major design fault in the eover has been eliminated although the assembly proeess must remain within speeial eontrol. Subsequently, the redesign solution was ehosen for further design development. 

In the event of failures due to lubrication problems, the failures should be thoroughly analyzed to determine if they were indeed caused by lubricant failure or incorrect maintenance procedures. Once the problem has been isolated, corrective action can be initiated to prevent subsequent similar failures—whether it requires changing lubricants or procedures. 

Despite these early successes in the commercialization of acrylic polymers, no acrylic PSAs were manufactured on a larger scale until many years later. One of the primary reasons for the initial commercial failure of the acrylic PSAs was their lack of cohesive strength. Unlike the higher Tg, plastic-like polymers obtained from monomers like methylmethacrylate, polymers synthesized from alkyl acrylates typically formed sticky, cold-flowing materials with little if any utility. 

The combinations of failures and non-failed conditions define the state of the pJani at the right branches. The damage associated with these plant damage states are calculated using thermal-hydraulic analyses to determine temperature profiles that are related to critical chemical reactions, explosions and high pressure. These end-states serve as initiators fot breaking confinement that leads to release in the plant and aquatic and atmospheric release outside ol the plant,... 

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