An analyst needs to determine the time when 10% of the turbine blades in a sample are expected to fail (i.e., B10 life). To determine performance, the blades are tested for crack propagation. The units are cyclically stressed and inspected every 100,000 cycles for crack length. Failure is defined as a crack length of 30mm or greater.
Five turbine blades were tested for crack propagation. The test units were cyclically stressed and inspected every 100,000 cycles for crack length. Failure is defined as a crack of length 30 mm or greater.
Fatigue failures are failures caused in components under the action of fluctuating loads. They are estimated to be responsible for 90% of all metallic failures since loads on the components usually are not constant but instead vary with time. Fatigue failures occur when components are subjected to a large number of cycles of the applied stress. With fatigue, components fail under stress values much below the ultimate strength of the material and often even below the yield strength. What makes fatigue failures even more dangerous is the fact that they occur suddenly, without warning. The failure begins with a minute crack that is so small that it may not be detected by non-destructive methods such as X-ray inspection. The crack may get initiated by internal cracks in the component or irregularities in manufacturing. Once a crack has formed, it propagates rapidly under the effect of stress concentration until the stressed area decreases so much that it leads to a sudden failure.
40 electronic components were tested to failure due to crack growth in solder joints as a result of repeated temperature cycling at three different elevated stress conditions. The associated data set is entered into an ALTA PRO standard folio, as shown below.
In this article, we introduced the Norris-Landzberg physics of failure model for crack growth in solder joints resulting from repeated temperature cycling in electronic devices. The relationship between the Norris-Landzberg model and the general log-linear model was presented, and ALTA PRO was used to estimate the Norris-Landzberg parameters for a given data set. A similar process can be used to analyze accelerated test data in ALTA for many physics of failure models with multiple stresses.
An analyst needs to determine the time when 10% of the turbine blades in a sample are expected to fail (i.e., B10 life). To determine performance, the blades are tested for crack propagation. The units are cyclically stressed and inspected every 100,000 cycles for crack length. Failure is defined as a crack length of 30mm or greater. The following table shows the results.
Our nominal stress distribution represents the stress of the part under no additional or external user-input loading. In the case of the B50 loading, the average user causes an acceleration of 0.679 g above nominal. In order to perform the fatigue analysis in DesignLife, we need to define the fatigue cycle. In this case, we will define it as going from nominal to the nominal plus the additional acceleration the user imparts onto the hinge. Therefore, our cycle is defined as going from 1 g to 1.679 g. DesignLife uses this information to calculate the change in stress due to the change in acceleration on every single node in the model. It then calculates the damage associated with that change in stress by looking at the fatigue curve and then calculates how many of those cycles the part can withstand before a crack is predicted to initiate for every single node in the model. The result is a contour plot of damage or, inversely, life. That is, how many times can we repeat that 1g to 1.679 g cycle until a crack will initiate. The life contour plot for the B50 case is shown below:
The Weibull++ degradation analysis folio allows you to extrapolate the expected failure times of a product based on measurements that reflect how some performance measure (e.g., increase in crack propagation, decrease in tread depth, increase in vibration, etc.) has degraded for sample units over a period of time. The software offers a choice of the Linear, Exponential, Power, Logarithmic, Gompertz or Lloyd-Lipow models to analyze the degradation data, and generates Degradation vs. Time plots on either a linear or logarithmic scale.
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Different surface treatments such as APA and grinding are essential routine steps for better resin bonding to zirconia. However, these surface treatments can deteriorate the mechanical properties of Y-TZP and Y-PSZ and possibly induce surface flaws and microcracks that can propagate under occlusal loads leading to a catastrophic failure [12, 21]. Occlusal loads are far below the flexural strength of zirconia. However, with pre-existing surface defects, intermittent occlusal forces may lead to the propagation of those cracks and eventually lead to a fracture [22, 23]. Fracture toughness measures the material resistance to crack propagation; hence it could be affected by the magnitude of surface flaws or cracks that are induced by different mechanical surface treatments . The effect of APA and grinding on the mechanical properties of HT zirconia has been less studied compared to LT zirconia . Therefore this study aimed to evaluate the effect of low APA and surface grinding on biaxial flexural strength, fatigue resistance, and fracture toughness of HT versus LT zirconia frameworks. The null hypothesis tested was that different surface treatments will not affect the biaxial flexural strength and fracture toughness of either HT or LT zirconia.
Surface grinding and APA were applied in the current study as mechanical surface treatments to zirconia as they are routinely performed in the clinical situation to improve the resin bonding to tooth structure or to the veneering porcelain . Further, grinding is commonly done during fit corrections of zirconia frameworks [12, 21, 34]. However, APA was employed, in a low-pressure mode, to decrease the possible critical surface flaws that act as stress concentration sites and potential crack origins under loads [35,36,37,38].
High translucency zirconia revealed a higher fatigue resistance, compared to LT zirconia, as it was associated with a lower percentage of reduction in residual strength due to its internal structure, larger grain size, and refined grain boundaries. Some studies found that the percentage of transformation toughening that hinders crack propagation in LT tetragonal zirconia was much higher than HT cubic zirconia [43,44,45,46,47,48], so it was expected for LT zirconia to be more resistant to fatigue compared to HT zirconia. Such a finding cannot be attributed to phase transformation alone. Still, it is directly related to the internal structure of the materials and the mechanism that larger grains might interrupt the propagation of crack tips [54,55,56,57,58].
The current study showed that the fracture toughness of HT zirconia was higher than that of LT zirconia which can be attributed to the larger grain size of the first  as there is a strong direct relationship between fracture toughness and grain size. High translucency zirconia was associated with relatively smaller critical crack sizes compared to LT zirconia. Rougher crack surfaces indicated that cracks traveled at grain boundary regions instead of splitting the grains, especially in its first stages. Larger grains mean longer crack paths, which could explain the higher fracture toughness observed for HT zirconia. Another study stated that the fracture toughness of zirconia is closely related to the transformation toughening ability as the transformation process itself helped in dissipating the energy associated with crack propagation . Nevertheless, an optimised internal structure is of prime importance as transformation toughening is a process limited to the presence of stresses, and regions, outside the stress field, will not benefit from this process.
Fatigue failures can occur in electronic devices due to temperature cycling and thermal shock. Permanent damage accumulates each time the device experiences a normal power-up and power-down cycle. These switch cycles can induce cyclical stress that tends to weaken materials and may cause several different types of failures, such as dielectric/thin-film cracking, lifted bonds, solder fatigue, etc. A model known as the (modified) Coffin-Manson model has been used successfully to model crack growth in solder due to repeated temperature cycling as the device is switched on and off. This model takes the form : 2b1af7f3a8