Investigation of the Fatigue Stress of Orthotropic Steel Decks Based on an Arch Bridge with the Application of the Arlequin Method

Orthotropic steel decks are widely used in the construction of steel bridges. Although there are many fatigue-evaluation methods stipulated by codes, unexpected fatigue cracks are still detected in some bridges. To justify whether the local finite element model commonly used in fatigue investigations on orthotropic decks can correctly instruct engineering practices, the Arlequin framework is applied in this paper to determine the full fatigue stress under traffic loads. The convergence on and validity of this application for orthotropic decks are checked. Results show that the Arlequin model for deck-fatigue analysis established in this paper tends to be an efficient method for complete fatigue stress acquisition, whereby the vulnerable sites of orthotropic steel decks under traffic loads are defined. Vehicles near the flexible components, such as hangers or cables, can have adverse effects on the fatigue durability of decks. Additionally, the total number of vehicles and their arrangement concentration also affect fatigue performance. Complex traffic conditions cannot be fully loaded in local models. Regardless of the gross bridge mechanics and deck deformation, the fatigue stress range is underestimated by about 30–40%. Such a difference in fatigue assessment seems to explain the premature cracks observed in orthotropic steel decks.

Features of Strain Hardening of Heterogeneous Aluminium Alloys to Enhance the Fatigue Durability

Heterogeneous aluminium alloys are in demand in the aviation industry, where the ability of the material to withstand fatigue loads is important. The topic of the article is the search for the most experimentally available methods of deformation effect on such materials in order to increase fatigue life. Unfortunately, previous studies were ambiguous due to the large number of factors influencing the fatigue of metal materials under the same type of mechanical load; so, we chose a dynamic load with pulse loading. It turned out that for heterogeneous 2024-T351 and D16CzATW alloys, shock–vibration loading (SVL) applied during static straining prolongs their further fatigue life at a certain magnitude of the deformation during the action of the pulse. For example, for the 2024-T351 alloy at the maximum stress of alternating load σmax = 400 MPa, the longest fatigue life should be expected at deformations εimp = 2–4%; and at the maximum stress of alternating (fatigue) loading of 440 MPa, it is at εimp = 3–5%. In comparison with the average values of fatigue life of the D16CzAT alloy in the initial state, fatigue life after processing increases at σmax = 340 MPa alloy by 11.6%, at a stress of σmax = 370 MPa, by 18.4%, at a stress of σmax = 400 MPa, by 21.2%. The positive effect of long-term exposure after treatment on fatigue life was also noted. The influence of the strengthening phases, such as the nanosize Θ-Al2Cu and S-CuAl2Mg particles, on the separate stages of pre-treatment of alloys and the effects of their quantities on total fatigue durability is investigated by statistical methods of transmission electron microscopy. The great attention is paid to the mechanism of formation of fatigue fracture embryos in the near-surface areas of the samples, for which analytical calculations and the experimental method of ultrasonic impact treatment (UIT) are used. It is shown that the use of UIT after SVL does not affect the fatigue life of the 2024-T351 alloy at a fatigue load frequency of 15 Hz, while the single UIT increases fatigue life of the alloy. It is concluded that the use of complex deformation loads accelerates the relaxation processes, which shorten fatigue life.

Predicting the Fatigue Life of a Ball Joint

The technical conditions and service life of steering elements of vehicles are an important factor directly affecting road safety. Therefore, high reliability of such kind’s components is required. In the paper, on the basis of the stand test, the fatigue durability of a ball joint of a steering tie rod is determined. It is elaborated together with a prediction for the further number of cycles, enabling to determine the technical state of the tested component containing its service life. The aim of the article is to select an appropriate mathematical model with respect to describing the relationship between the moment of force and the fatigue cycles performed for the ball joint of a steering rod of a vehicle with a GVW above 3.5 tonnes, and identifying the model’s parameters. As a result, the limit number of loading cycles after which the examined joint does not meet safety requirements is estimated.

Modification of the Stamp Topological Optimization Taking into Account Cyclic Fatigue based on the Finite Element Approach

The study is devoted to optimizing the volume of stamping tools used in pressure processing processes. The relevance of the research is due to the active development of additive technologies and the possibility of producing stamping tools from plastic of optimal shape, which has an important practical significance in the manufacture of thin-walled products in the aviation and automotive industries. The purpose of the study was to carry out a mathematical formulation of the problem of topological optimization of a forming die made of a polymer material with restrictions on fatigue durability and minimum volume. The task of topological optimization was to maximize the stiffness of the die under multicyclic loading. The vector description of topological optimization was based on the finite element approach. The optimization model was built on the basis of the solid isotropic material penalization method with the introduction of additional restrictions in the model of searching for pseudo-densities of the material, taking into account the duration of the force action on the stamp under multicyclic loading. In view of the nonlinearity of the resulting system of equations, the solution of the conditional optimization problem is proposed to be carried out by constructing the Lagrange objective function and using the Lagrange multiplier method. The result of the study is the proposed approach to the topological optimization of the stamp, taking into account the multicyclic loading and restrictions on the desired volume.

Role of Nominal Stress State On Cyclic Fatigue Durability of SAC305 Grain-scale Solder Joints

Solder joints in microelectronic assemblies experience a combination of extensional, shear and multiaxial loads due to printed circuit board (PCB) flexure during thermal cycling or during vibrational loading of constrained PCBs. Although, a significant amount of research has been conducted to study failures of solder joints under pure-shear loading, most of the current literature on cyclic tensile loading of solders is on long dog-boned monolithic solder coupons. Unfortunately, such specimens do not capture the critical interactions between key micro-scale morphological features (such as grain orientation, grain boundaries, IMCs and substrates) that are believed to play important roles in the fatigue of functional solder joints under life-cycle loading. Therefore, this paper uses a combination of experiments and finite element analysis to investigate the differences in mechanisms of cyclic fatigue damage in Sn-3.0Ag-0.5Cu (SAC305) few-grained microscale solder joints under shear, tensile and multiaxial loading modes at room temperature. The fatigue durability test results indicate that tensile loads are more detrimental compared to shear loads. Tensile vs. shear loading modes are found to cause distinctly different combinations of interfacial damage vs. internal damage in the bulk of the solder (transgranular and intergranular damage), which correlates with the differences observed in the resulting fatigue durability. The test results also confirm that fatigue durability is affected not only by the cyclic equivalent strain amplitudes, but also by the severity of the stress-triaxiality as hypothesized in models such as Chaboche model.