Kinetostatic analysis, manufacturing, and experimental application of a press machine based on Stephenson II mechanism

Press machine tools are often used in important industrial establishments, such as automobiles, aerospace, and aviation; these machine tools must be produced with high precision. Therefore, studies related to improving press tools and enhancing their precision are being conducted. In this study, a press machine tool based on the Stephenson II mechanism is proposed. Compared to that of conventional crank presses, this mechanism increases the slider balance using a ternary link and unique connecting rods. Thus, the slider precision can be improved with a small addition to the mechanism, and load transmission can be ensured in a balanced manner. To test the contribution of the mechanism, dynamic analysis is performed using the kinetostatic method, and the dynamic data of the mechanism are obtained. Subsequently, a press machine prototype is designed and manufactured. The experimental results are verified against the theoretical results, confirming that the proposed press machine tool based on the Stephenson II mechanism has better characteristics than those of the conventional press machine owing to the favorable distribution of forces on the slide and lower reaction to the slide guides.

Biomechanics of a calcar loading and a shortened tapered femoral stem: Comparative in-vitro testing of primary stability and strain distribution

Purpose The most common femoral short stems available on the market can, in principle, be divided with regard to their anchoring concepts into a calcar loading and a shortened tapered design. The purpose of this study was to compare the primary stability and stress-shielding of two short stems, which correspond to these two different anchoring concepts. Methods Using seven paired fresh frozen human cadaver femurs, primary axial and rotational stabilities under dynamic load (100–1600 N) were evaluated by miniature displacement transducers after 100,000 load cycles. Changes in cortical strains were measured before and after implantation of both stem types to detect implant-specific load transmission and possible stress-shielding effects. Results Reversible and irreversible micromotions under dynamic load displayed no significant differences between the two implants. Implantation of either stem types resulted in a reduction of cortical strains in the proximal femur, which was less pronounced for the calcar loading implant. Conclusions Both short stems displayed comparable micromotions far below the critical threshold above which osseointegration may disturbed. Neither short stem could avoid proximal stress-shielding. This effect was less pronounced for the calcar loading short stem, which corresponds to a more physiological load transmission.

Sacrificial Cladding with Brittle Materials for Blast Protection

In the following work, sacrificial claddings filled with different brittle materials were investigated, from concrete foam to granular media. They were subjected to blast loading using an explosive driven shock tube, while a sensor measures the load transmission and a high speed camera records the compression of the core. From a macroscopic point of view, concrete foam and granular media can act efficiently as a crushable core but differs greatly in terms of energy dissipation mechanisms. To compare them, granular media was at first treated as a cellular material, and different key parameters (plateau stress, densification strain) were computed using the energy absorption efficiency methodology. The presented tests results, coupled with observation in literature, allow a better understanding on the crushing process of a granular media. In particular, granular media tend to work as a core even for low intensity load, contrary to more classical crushable core.

Ultrasonography in physiotherapy and rehabilitation

There is an interrelation with ultrasound / physiotherapist and the duty of the physiotherapist to know how to perform ultrasound examinations alone, not for diagnostic purposes, to follow the evolution of the therapeutic cycle of physiotherapy. For this reason, ultrasound image analysis (US) is a promising non-invasive approach that uses load-dependent changes in the intensity of the echo to characterize the rigidity of muscle and tendon tissue. The purpose of this contribution is to improve the use of ultrasound images (US) and the role of the physiotherapist, who are able to detect localized changes, in particular in stiffness of the tendon due to partial and full-thickness tendon tears. Image intensity information is less sensitive for identifying load transmission variations resulting from partial thickness cuts initiated on the joint side. Ultrasound images can be useful for quantitatively assessing the variations dependent on the tendon load and muscle stiffness in physiotherapy and that the interruption of the behavior of the acousto-elastic ultrasound images can be indicative of substantial damage to the muscle or tendon.

Mapping of Nanomechanical Properties of Enamel Surfaces Due to Orthodontic Treatment by AFM Method

Background: Atomic force microscopy imaging was used to study the structural topography of enamel crystals in healthy and affected enamel. The correlation of topographic images with nanomechanical properties allows for the assessment of morphology and properties at the micro- and nano-meter level in three dimensions simultaneously. Methods: A total of 60 premolars were treated like teeth during orthodontic bonding and debonding procedures. Every stage was observed in AFM. Surface roughness, image surface area difference, mean Young’s modulus, and mean adhesion force (the force of attraction between the scanning blade and the surface averaged over the image) were determined for the following areas: the central part of the surface, responsible for load transmission; the top of the surface, subject to the most abrasive wear; the lower part of the surface, responsible for the transport of fluids. Results: The highest roughness occurred on the etched surface—average 63 nm, followed by the intact enamel—8.3 nm, cleaned enamel—7.0 nm, and the resin-coated surface—5.4 nm. Conclusion: Etching increases enamel roughness and reduces hardness. Resin reduces roughness of the etched surface and increases hardness. The intact enamel has the highest hardness. The enamel smoothness is greater after polishing than in the intact enamel.

Load Path Transmission in Joining Elements

The mechanical properties of joined structures are determined considerably by the chosen joining technology. With the aim of providing a method that enables a faster and more profound decision-making in the spatial distribution of joining points during product development, a new method for the load path analysis of joining points is presented. For an exemplary car body, the load type in the joining elements, i.e. pure tensile, shear and combined tensile-shear loads, is determined using finite element analysis (FEA). Based on the evaluated loads, the resulting load paths in selected joining points are analyzed using a 2D FE-model of a clinching point. State of the art methods for load path analysis are dependent on the selected coordinate system or the existing stress state. Thus, a general statement about the load transmission path is not possible at this time. Here, a novel method for the analysis of load paths is used, which is independent of the alignment of the analyzed geometry. The basic assumption of the new load path analysis method was confirmed by using a simple specimen with a square hole in different orientations. The results presented here show a possibility to display the load transmission path invariantly. In further steps, the method will be extended for 3D analysis and the investigation of more complex assemblies. The primary goal of this methodical approach is an even load distribution over the joining elements and the component. This will provide a basis for future design approaches aimed at reducing the number of joining elements in joined structures.