Numerical and experimental investigation of flat-clinch joint strength

The striving for energy savings by lightweight construction requires the combination of different materials with advantageous properties. For joining sheet metal components, clinching offers a good alternative to thermal joining processes. In contrast to thermal joining processes, the microstructure in the joining zone remains largely unaffected. Conventional clinch joints, however, have a protrusion on the underside of the joint, which restricts their use in functional and visible surfaces. Flat-clinching minimizes this disadvantage by using a flat anvil instead of a die. Due to the flatness on the underside, it can be used in visible and functional surfaces. This paper deals with the increase of joint strength by using an auxiliary joining element (AJE) in the second forming stage. To achieve optimum improvement in the joint strength of an aluminum Al99.5 H14 sheet metal joint and to save costs, the AJE was varied numerically in terms of volume, material and basic shape. The geometric parameters (e.g., interlocking f and neck thickness tn) do not allow direct derivation of the joint strength. For this reason, the 2D clinch model was extended for the first time to include 3D load models (cross tension, shear tension). To validate the numerical results, optimized flat-clinch joints with AJE and the associated load tests were implemented experimentally. The numerical models were used to improve the process development.

Demountable Column - Girder Joint

Traditional precast reinforced concrete structures are characterised by joints of individual components executed with the use of cement grouts or mortars, or by welding reinforcement. The joints produced in this way cannot be demounted in the case of need without damaging the precast components. Demountable precast structures with a long life cycle enable repeated assembly and demounting thus contributing to the saving of the basic input resources and the environment. The main feature of demountable precast structures are patent-protected joints which allow the assembly of the precast components without the necessity of using “wet” processes. The article addresses the characteristics of a demountable girder - column joint. It presents the results of static load tests carried out within extensive experimental research. To conclude, the article specifies the benefits and the applications of demountable structures.

Joining of CFRT-steel hybrid parts via hole-forming and subsequent pin caulking

In times of increasing global warming, the awareness of the necessity for significant CO2 reduction is growing. Especially in the transport and aerospace sector, lightweight construction has potential to achieve emission reduction goals by reducing the overall vehicle weight. Thereby, adding lightweight fibre-reinforced composites to materials such as steel and aluminium is used to achieve weight savings. Furthermore, continuous-fibre-reinforced thermoplastics (CFRTs) begin to replace more traditional thermoset thermoplastics due to their easier bulk production and uncomplicated storage. Hybrid parts often consist of a CFRT and a higher strength metal component. Here, the joining process poses the main challenge, due to different chemical and physical properties of the components. In the current state of the art, riveted and bolted joints are commonly used, leading to increased weight due to auxiliary elements and requiring precise bolt holes often destroying load-bearing fibres. Joining with cold formed pin structures is an innovative and versatile joining process, which avoids the need for auxiliary elements. These pins are subsequently inserted in warm formed holes in the CFRT component and then caulked to create a form-fitting hybrid joint. To obtain a fundamental understanding of this joining process, hole-forming and pin-caulking, are investigated in this study. First, the hole-forming with IR-radiation is investigated with regard to suitable process parameters and resulting fibre morphology. The formed holes are consequently mechanically characterized. Second, the caulking-process is investigated by iteratively upsetting a pin and subsequently measuring the geometry. Based on these findings two different suitable caulking degrees are defined and samples for mechanical as well as microscopic investigations are manufactured. The created joints are first investigated via micro-sections and reflected light microscopy to identify possible damage in the CFRT component, which can result from the pin caulking process. Second, a mechanical characterisation under shear load as well as pin extraction loads normal to the sample surface is conducted and the normal load tests are compared with the bearing strength of CFRT samples.

Numerical Modelling of Various Aspects of Pipe Pile Static Load Test

Due to the development of dedicated software and the computing capabilities of modern computers, the application of numerical methods to analyse more complex geotechnical problems is becoming increasingly common. However, there are still some areas which, due to the lack of unambiguous solutions, require a more thorough examination, e.g., the numerical simulations of displacement pile behaviour in soil. Difficulties in obtaining the convergence of simulations with the results of static load tests are mainly caused by problems with proper modelling of the pile installation process. Based on the numerical models developed so far, a new process of static load test modelling has been proposed, which includes the influence of pile installation on the soil in its vicinity and modelling of contact between steel pile and the soil. Although the presented method is not new, this is relevant and important for practitioners that may want to improve the design of displacement piles. The results of the numerical calculations were verified by comparing them with the results of pipe pile field tests carried out in a natural scale on the test field in Southern Poland.

COVID-19 impact on testing, diagnosis and care of people with sexually transmitted infections in a low human development region, Minas Gerais, Brazil

This study aimed to analyze the impact of the COVID-19 pandemic on the care of people with Sexually Transmitted Infections (STIs) in a region of low human development, located in Minas Gerais, Brazil. Methods: The number of monthly procedures during pandemic period, January to December 2020, and comparison period, January to December 2019, in a SUS regional clinic, a reference for STIs, were analyzed. Visits were categorized into follow-up appointments, rapid tests, viral loads and first appointment due a recent diagnosis. Comparison between both periods was performed by frequency analysis, difference in the mean monthly attendances (DM) and prevalence ratios (PR), considering ratio between the proportion of attendances in the pandemic period/proportion of attendances in the comparative period. During the pandemic period, the average number of monthly consultations reduced for all consultations (DM = -105.25) and categories. Proportion of consultations reduced for rapid tests (PR = 0.46; 95% CI = 0.41-0.52) and first consultation due recent diagnosis (PR = 0.90; 95% CI = 0.65-1, 25), procedures that are usually scheduled by the user. There was an increase in the proportion of follow-up visits (PR = 1.18; 95% CI = 1.09-1.27) and viral load tests (PR = 1.41; 95% CI = 1.32-1, 88), monitoring procedures usually scheduled by the clinic. There was a trend to maintain risk exposure for STIs. Conclusion: These findings may guide better strategies to care for individuals with STIs.

Identification of residual force in static load tests on instrumented screw displacement piles

Occurrence of the so-called residual force of an unknown value significantly disturbs interpretation of static load tests performed on piles equipped with additional measuring instruments. Screw displacement piles are the piling technology in which the residual force phenomenon is very common. Its formation mechanism is closely related to the installation method of this type of piles, which initiates generation of negative pile skin friction without any additional external factors. Knowledge of the value and distribution of a residual force (trapped in a pile shaft before starting the load test) is a necessary condition for the proper interpretation of instrumented pile test results. In this article, a clear and easy-to-use method of residual force identification, based on the analysis of shaft deformations recorded during pile unloading is presented. The method was successfully verified on two pile examples and proved to be effective and practical.