Stress analysis, a fundamental aspect of engineering and design, is critically dependent on experimental methods, with photoelasticity being a key technique. Despite its effectiveness, ...photoelasticity is often limited by subjective human interpretation, leading to variable stress measurement results. To address this, we have concentrated on the practical applications of this method, employing a circular disc analyzed under various compressive loads. Our research introduces a novel algorithm specifically developed for processing photoelastic images. This algorithm enhances the clarity of thinned fringes, enabling more precise measurement of the principal stress differences. Our findings indicate that the digitally processed photoelastic images align closely with analytical solutions, suggesting a more reliable and consistent approach to stress analysis. This advancement mitigates the subjectivity inherent in traditional photoelastic methods, thus improving the accuracy of stress measurement. The implications of this study are significant for the broader field of engineering. The developed methodology can be applied to diverse scales of instruments and facilities, offering a versatile tool for identifying stress patterns. Overall, our work also improves the accuracy of such a tool and technique, making it more useful for failure analysis scenarios understanding.
This paper aims to identify appropriate input motions for use with an effective-stress analysis procedure for liquefaction assessment of sites affected by the 2010 Mw7.1 Darfield and 2011 Mw6.2 ...Christchurch, New Zealand earthquakes. Within-event recorded surface ground motions at selected ‘reference’ strong motion station (SMS) sites are used to derive representative base-input motions for the effective-stress analyses at the target sites. Each selected seed motion is deconvolved to obtain the respective ‘engineering bedrock’ motion, and then scaled in amplitude to account for differences in the source-to-site distance between the reference station (deconvolution site) and the target site. The performance of each derived input motion and associated simulation of ground response are evaluated by comparing recorded surface motions to those predicted by 1D effective-stress analyses at 13 SMS sites throughout Christchurch. Results from the effective-stress analyses demonstrate the ability of the adopted analysis procedure to capture key aspects of ground response in liquefying deposits, but they also highlight the sensitivity of the predicted surface motion to the input excitation at the base. The study shows that careful selection of seed motions for deconvolution, from reference SMS sites which are compatible with the target site in key source-to-site path characteristics (i.e. distance, azimuth, and basin geometry), and appropriate scaling of the deconvolved motions are essential for a good prediction of the surface ground motion at the target site. Findings from this study will be used to inform the definition of input motions for effective-stress analyses of 55 well-documented case-history sites in Christchurch.
•Effective stress analyses of strong motion station sites throughout Christchurch are scrutinized.•Input motions are derived based on within-event records from selected ‘reference’ recording stations.•Reliable estimation of input motion requires careful record selection and appropriate modification of the selected record.•Key aspects of ground response in liquefying deposits are well captured by the analyses.•Observed bias is mainly due to the absence of representative seed records for some areas.
The high-temperature reliability of active metal brazed copper (AMC) on Si^sub 3^N^sub 4^ ceramic substrates used for fabricating SiC high-temperature power modules was investigated under harsh ...environments. The AMC substrate underwent isothermal storage at 300°C for up to 3000 h and a thermal cycling test at -40°C to 300°C for up to 3000 cycles. During isothermal storage at 300°C, the AMC substrate exhibited high reliability, characterized by very little deformation of the copper (Cu) layer, low crack growth, and low oxidation rate of the Cu layer. Under thermal cycling conditions at -40°C to 300°C, no detachment of the Cu layer was observed even after the maximum 3000 cycles of the experiment. However, serious deformation of the Cu layer occurred and progressed as the number of thermal cycles increased, thus significantly roughening the surface of the Cu metallized layer. The cyclic thermal stress led to a significant increase in the crack growth and oxidation of the Cu layer. The maximum depth of the copper oxides reached up to 5/6 of the Cu thickness. The deformation of the Cu layer was the main cause of the decrease of the bond strength under thermal cycling conditions. The shear strength of the SiC chips bonded on the AMC substrate with a Au-12 wt.%Ge solder decreased from the original 83 MPa to 14 MPa after 3000 cycles. Therefore, the cyclic thermal stress destroyed the Cu oxides and enhanced the oxidation of the Cu layer.PUBLICATION ABSTRACT
Adhesive bonding is increasingly being considered by engineers for load-bearing joints to complement, or supplement, traditional mechanical fasteners for a large variety of structural materials, ...including fibre-reinforced polymers, timber, and steel. However, practitioners are still largely applying analysis and design methods, including codes and standards, that rely heavily on fudge factors. This is not due to the relative novelty of the joining technique, and the complexity of the associated mechanics. This paper guides the reader through some of the most important aspects of adhesively bonded joints, and the reasons why classical mechanics can only be applied in conjunction with fudge factors. Subsequently, the principles of fracture mechanics (FM) are presented; it is shown that, despite its conceptual strengths, FM is rather difficult to implement, as it introduces mechanical concepts practitioners are not familiar with. Then probabilistic methods (PM) are introduced; it is shown that PM can be considered as an extension of classical mechanics, as they can be easily implemented as a post-processing routine of the latter. Additionally, it is shown that PM, unlike FM, neither require specific test procedures for characterisation, nor complicated numerical analyses. Lastly, the paper offers a step-by-step guide for the implementation of PM for the dimensioning of adhesively bonded joints. The second part of this paper illustrates the latter analysis and design of adhesively bonded joints on a series of examples involving FRP, timber, and steel.
To evaluate the effect of thermomechanical dynamic loading on the retention of telescopic mandibular overdentures with different metallic and nonmetallic material combinations.
Four groups were ...tested: (1) ZP (zirconia abutments/PEEK framework); (2) PP (PEEK abutments/PEEK framework); (3) TP (titanium abutments/PEEK framework); and (4) TG (titanium abutments/gold copings/cobalt-chromium framework). Each specimen contained four implants positioned over a polyvinylchloride-cylindrical base. After 10,000 removal/insertion cycles, the specimens were subjected to thermomechanical dynamic load in a chewing simulator for 1,200,000 loading cycles, corresponding to 5-year clinical fatigue. A screw was used to receive the chewing load, and 0.5 mm was permitted between the screw and the metal top fixed into the base to simulate the resilience of the posterior residual ridge tissues. Vertical chewing loads of 60 N were applied at a speed of 30 mm/second. Thermocycling was applied with a temperature ranging between 5°C and 55°C. The retentive force was measured using a universal testing machine 10 times before and after the thermomechanical dynamic loading test with a speed of 8 mm/second.
The mean retentive force increased significantly from 13.2 (± 4.6) N to 16.4 (± 6.1) N in group ZP (P = .002), while in group TP, it decreased significantly from 4.9 (± 2.1) N to 3.3 (± 1.7) N (P = .046). There was no statistically significant change in the retentive force for groups PP and TG.
The investigated metallic and nonmetallic combinations of double-crown-retained mandibular overdentures maintained acceptable levels of retention after thermomechanical dynamic loading. Further laboratory and clinical studies are needed before their routine clinical use can be recommended.
Laser surface treatment was used as a surface preparation method for adherend prior to adhesive bonding, which significantly improved the fracture mode from mixed to cohesive and consequently ...increased the lap-shear tensile strength by 27.5% and 28.2% for aluminum alloys AA7075 and AA6022 adhesive-bonded joints, respectively. Nevertheless, the laser-treated AA7075 joint exhibited a 13.9% higher strength compared to laser-treated AA6022 joint although both joints showed cohesive fracture modes, which was attributed to smaller adherend deflection of laser-treated AA7075 joint than that of laser-treated AA6022 joint. Digital image correlation technique was applied to monitoring the deflections of laser-treated AA7075 and AA6022 joints during lap-shear tensile testing, and the stress analysis of adhesive-bonded lap-shear joints was conducted by finite element simulation. It was found that the deflection angle of the laser-treated AA6022 joint reached to 6.1° at the peak tensile load and was ∼69% larger than that of laser-treated AA7075 joint (i.e. 3.6°), which resulted in a mixed stress state with higher peel stress (i.e. ∼8 MPa) on edges of adhesive bonding region and consequently led to a premature fracture due to the low peel resistance of adhesive-bonded joints. Furthermore, the effect of decreased adherend deflection on lap-shear tensile strength was investigated, and a linear increase of lap-shear tensile strength was found with the decrease of deflection angle for adhesive-bonded joints showing cohesive fracture modes.
The present manuscript gives the description of findings which took importance during the design and analysis of the structure of heavy duty hauler machine ordered by Gol-e-Gohar iron ore complex in ...Iran. Stress and deformation analysis was indeed the heart of the project and the key of its success. The challenging problem of evaluation of value and behaviour of active loads was taken under consideration precisely and all participated external forces were included in analysis. Since the present case is a moving structure, the loading evaluation should be included in all critical experienced conditions through the operation. The inertial forces due to acceleration and road bump have the governing role and have been evaluated and considered in analysis. After precise and complete evaluation of external loads and applying the correct boundary conditions, the simulations for stress analysis have been performed in ANSYS. The main findings of the present study were the optimized decision for the geometry of several important load carrying elements and appropriate reinforcement of the risky positions which was the result of the correct knowledge of the mechanics of problem. Finally, the structure was manufactured with the total weight of about 38 ton and load carrying capacity of 120 ton including the dynamic effects. After succeeding in the initial loading, the operational loading in real conditions in mine ramp has been carried out gradually and the machine is currently working in desired predicted form.
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•Residual stress distribution in locally quenched and tempered 50CrMo4 steel using synchrotron transmission techniques•Relationship between residual stresses, retained austenite ...content and hardness for two specific local heat treatment states•Macrosegregations reduce the magnitude of residual stresses and retained austenite content in the quenched 50CrMo4 steel•Geometry and quenching rate have a greater influence on the residual stresses than the chemical composition of 50CrMo4 steel
This work investigates the in-depth residual stress distribution and retained austenite content in plates that were wire eroded from one locally quenched and one locally quenched-tempered 50CrMo4 cylinders by the means of high-energy X-Ray synchrotron transmission techniques. The main challenge was to interpret the results from all diffraction angles to obtain meaningful validation data for future computer simulations of induction hardening and tempering. The results were discussed in relation to hardness distribution. With the help of the applied measurement technique, even the effects of macro-segregation near the longitudinal sample axis can be detected. In inductively heated and quenched cylindrical specimens of 50CrMo4 specimens, macro-segregations near the longitudinal sample axis lead to a reduced retained austenite content, which shifts the axial stresses towards tensile stresses. Comparing the results with those from the literature, it can be seen that variations in the chemical composition of the sample within the specification range of the steel grade have less influence on the residual stress distribution in the induction hardened samples than the sample geometry and/or the quenching rate.
Abstract Statement of problem IPS e.max CAD and IPS e.max Press (Ivoclar Vivadent AG) are lithium disilicate glass ceramics marketed as interchangeable materials indicated for the same clinical uses. ...However, different crystal sizes of lithium disilicate are formed during the processing of each of these materials, a factor that could lead to significantly different mechanical properties. As mechanical failure is always associated with a crack-initiation/crack-propagation process, fracture toughness (KIC ) values could be useful in comparing different ceramics and possibly predicting clinical performance. Purpose The purpose of this in vitro study was to determine and compare the KIC of IPS e.max CAD and IPS e.max Press. Material and methods The notchless triangular prism (NTP) specimen KIC test was used to determine and compare the KIC of IPS e.max Press and IPS e.max CAD. Twenty 6×6×6×12-mm NTP specimens of each material were prepared. IPS e.max CAD blocks were cut, ground, and then crystallized, while IPS e.max Press specimens were prepared by pressing IPS e.max Press ingots into molds obtained from 6×6×6×12-mm wax prisms, using the lost wax technique. Each specimen was mounted into a specimen holder, and custom grips were used to attach the specimen holder assembly to a computerized universal testing machine (model 4301; Instron Canada, Inc). The assembly was loaded in tension at a crosshead speed of 0.1 mm/min, and the KIC value was calculated based on the recorded maximum load at fracture. Fractured surfaces were characterized using scanning electron microscopy (SEM). Results were statistically analyzed using Weibull statistics and the Student t test (α=.05). Results Significantly ( P <.05) higher KIC value was determined for IPS e.max Press than for IPS e.max CAD and, based on the Weibull modulus (m), IPS e.max Press was also more reliable. Fractured surfaces, characterized by SEM, showed a marked difference between the 2 materials, suggesting a more complete crystallization in IPS e.max Press, which was most likely responsible for the higher KIC determined. Conclusion Within the limitations of this in vitro study, the results suggest that IPS e.max Press is superior to IPS e.max CAD with regard to the KIC and characteristic Weibull parameters.
Nanocrystalline materials offer very high strength but are typically limited in their strain to failure, and efforts to improve deformability in these materials are usually found to be at the expense ...of strength. Using a combination of quantitative in situ compression in a transmission electron microscope and finite-element analysis, we show that the mechanical properties of nanoparticles can be directly measured and interpreted on an individual basis. We find that nanocrystalline CdS synthesized into a spherical shell geometry is capable of withstanding extreme stresses (approaching the ideal shear strength of CdS). This unusual strength enables the spherical shells to exhibit considerable deformation to failure (up to 20% of the sphere's diameter). By taking into account the structural hierarchy intrinsic to novel nanocrystalline materials such as this, we show it is possible to achieve and characterize the ultrahigh stresses and strains that exist within a single nanoparticle during deformation.
