Pavel Solfronk

Failure of sternal wires depends on the number of turns and plastic deformation: combined experimental and computational approach

OBJECTIVES The number of turns at the end of a wire closure is not described or discussed in any cardiosurgical guidelines. The hands-on experience of the surgeon plays a significant role. The aim of this work was to clarify the relationship between the number of turns of the suture and the resulting strength of the sternal fixation. METHODS The study was performed in 2 independent steps. The first step was a finite element simulation, where the stress and strain distribution of the sternal fixation was observed. The second step included the experimental set-up and the statistical evaluation of the results. RESULTS Our study showed that the failure force rose linearly as the number of turns increased. The lowest average measured force was 370 N (3 turns); the highest was 430 N (7 turns). The failure modes were either untwisting of the wires or rupture of the closure, which is controlled by the number of turns. As the number of turns increases, superficial cracks can occur. CONCLUSIONS Based on our results, the 5-turn option is the best solution for the closure. The failure force is still double the value reported in the literature, so there is a high safety margin for failure. The failure mode is untwisting; hence, no unexpected fracture can occur, and there is still an elastic core in the cross-section of the wire.

Influence of Deformation on the Damage of Zn-Mg Based Protective Coating

These days are in the automotive industry going to be still more and more used new types of protective coatings on the Zn-Mg basis. The advantage of these coatings is their excellent protection against corrosion of basic material. On the other hand disadvantage is mainly their low formability which takes effect at own stamping process. Such paper deals with the research influence of the deformation on the damage process of this coating. Size of deformation at different stress states was measured with the help of photogrammetry (system ARAMIS). Coating damage process at these stress states was monitored by means of optical and electron microscopy. Results of protective coating Zn-Mg damage process are presented in the form of strain distribution maps and images from optical and electron microscope.

STRENGTH OF THE ADHESIVE JOINTS AT THE CAR-BODY PARTS FROM THE AHSS WITH AL-SI COATING

The paper deals with the monitoring the utility properties of the Al-Si coating which is applied by means of the hot dip coating on the ultra-high strength sheet 22MnB5 (martensite steel alloyed by boron). These sheets are used at the car-body design as the safety elements (bumpers, reinforcement posts). Individual parts are jointed also by the adhesive bonding methods. Evaluation of the material surface protection layers is carried out in dependence on the time of material heating in the furnace during thermal treatment and subsequent influence of this layer on the adhesive joint strength and failure pattern. To compare adhesive joint strength is used epoxy adhesive from two producers. Results provide information about behavior of the ultra-high strength sheets adhesive joints strength properties as a criterion for suitability to apply coatings AlSi in the series production of cars.

INFLUENCE OF TESTING METHODS ON THE FINAL VALUES OF THE MODULUS OF ELASTICITY E

In the area of elastic deformation there is linear dependence between the applied stress and final deformation, which is described by the Hooke ́s law. Thus stress and strain are proportional to each other and constant of proportionality is termed as modulus of elasticity (even. Young ́s modulus). So this material constant characterizes the elastic deformation behavior of the given material and its magnitude represents the very important material constant in all industrial branches and mainly determines the dimensions for the given parts. That is why it ́s truly very important to precisely measure its values for different materials. Because of this were in this article used two methods for measurement Young ́s modulus E (MPa) – static tensile test and three-point bend test. Main aim was to obtain statistical evaluation about influence of these testing methods on the final values of modulus of elasticity.

SPRING-BACK PREDICTION FOR STAMPINGS FROM THE THIN STAINLESS SHEETS

The metal forming technology is (mainly due to the automotive industry) one of the most dynamically developing branch of the engineering industry. Continuous effort to achieve the top technological level and car ́s safety factor at keeping the low price level means necessity to still implement into the own production process the newest mathematical models of these technological processes. Thus these days represents utilization of the numerical simulations an essential part for the car shape lay-out design, for determination the basic technological operations and also e.g. for stamping tools shape optimization. Alongside such implementation of the newest materials into production reveals necessity to develop new and more precise computational models of materials deformation behavior as well as models designed for spring-back prediction. Nowadays, in the branch of the metal forming technologies, there are several truly top software among which also belongs software PAM-STAMP 2G. In this article is evaluated influence of the computational model on the numerical simulation accuracy by PAM-STAMP 2G at the spring-back prediction. For the deformation analysis it was chosen stainless sheet material DIN 1.4301 and for the spring-back prediction were used two anisotropic computational models termed as Hill-48 and Vegter in combination with the kinematic hardening model termed as YOSHIDA UEMORI. Accuracy of the measured results from the individual computational models is evaluated by the compliance of the carried out experiment and results from the numerical simulations. For the own experiment was chosen test where material is drawn over the drawbead and drawing edge.

TEMPERATURE INFLUENCE ON THE CHANGE OF THE SANDWICH MATERIAL ADHESIVE PROPERTIES

The automotive manufacturing represents one of the most developing segments of the engineering industry. The persisting tendency of designers to achieve the best technological level, car ́s safety level and also ecological running at keeping the low price level means necessity to still implement into own production new types of materials. Among these materials also belong so-called sandwich materials which combine steel sheets with the plastic core. These materials are used in the car design due to their lower weight and excellent acoustic properties. As a disadvantage of such materials there is lower temperature stability and worse technological processability. This paper deals with the evaluation temperature influence on the change of the sandwich material mechanical properties. For tests there were selected the characteristic mechanical tests for different loading types in light of the adhesive properties testing – the lap shear test and the T-peel test. The range of the testing temperature was from -40°C up to 80°C and was chosen with respect to the commonly used criterions for temperature resistivity of parts designed for the car-body design.

Adhesive Bonding Technology at Car - Body Structure – Application of New Coating with Layer Zn/Mg

The paper deals with the application possibilities of new coatings types on the basis of Zn/Mg and their utilization at car-body production Comparison is done by evaluation bonded joints strength acc. to ISO 11339 for commonly used zinc-coated sheet at production car-body stampings (HDG Z100) with layer of new type on the basis of zinc/magnesium (ZM). Such utilization of new materials also means necessity to carry out test of the individual bonded car-body parts utility properties, mainly at peel loading, in dependence on adhesive type simultaneously with regard to the lubricant which is used in the technological process drawing of stampings and temperature under which is joint loaded. To guarantee required joints quality is one of the crucial criterions for applications new types of coatings in mass production.

X-Ray Diffraction Analysis of Zn-Mg Coating in Dependence on Deformation

The Zn-Mg coatings are considered as the next generation of steel covering to be used in automotive industry since they improve the corrosion resistance of the base material. The article is focused on the X-ray diffraction analysis of Zn-Mg coating in dependence on strain. The specimens made from a material, which has Zn-Mg coating, were gradually deformed until they became totally fractured. Subsequently, the specimens´ surface layer was analysed using X-ray diffraction. X-ray diffraction methods are used for evaluation of the qualitative changes in the real structure of the polycrystalline material. The modification of the real structure is considered as a degree of plastic deformation, change of crystallite size and their orientation depending on deformation.

Change of Tribological Properties of Zn-Mg Coating in Dependence on Deformation

Protective coatings on the basis of Zn-Mg are still more a more used in present engineering industry. However their wider using (e.g. in the automotive industry) is still limited by unsufficient and pure knowledge about their behavior in dependence on deformation. Thus this paper is focused on testing tribological properties and their change in dependence on size of deformation. That is why there was used tribological strip drawing test where samples were firstly deformed on different values (15% and 30%). Subsequently were these strips drawn between hardened and non-hardened jaws and there were evaluated different forces necessary to draw a strip and friction coefficient was calculated. Main results (mainly course of friction coefficient on pressure and deformation) were shown as graphs and tables.

Adhesive Bonding Joints of Coating with Zn/Mg Layer on Sheets for Car-Body Panels at Temperature Loading

The paper deals with the monitoring of utility properties of new coating type on the basis of Zn/Mg (ZM). For the comparison there was used commonly used coating in the series production of car-body panels on the basis of zinc (Z100). Measured results markedly contribute to improve production systems of car-body adhesion bonding on the basic of performed evaluation of applied coatings types utility properties quality with regard to influence of temperature and corrosion environment. Testing was carry out by T-peel test acc. to ISO 11339 when such type of loading represents crucial bonding fracture type. Thus results reveal information about behavior of adhesive joints strength properties together with the type of fracture as a criterion for suitable application of new coatings types on the basis of Zn/Mg and their implementation into series production of automobiles.