This work describes the thread rolling as a real object and its physical and mathematical modelling. An incremental modelling and numerical solution of the contact problem between movable elastic or rigid tool and elastic/visco-plastic bodies developed in [ is adopted to the numerical simulation of thread rolling process for the case of rigid tool (threading head) and elastic/visco-plastic body (pipe or bar). An update Lagrangian formulation was used to describe nonlinear phenomena on a typical incremental step. For solution of discrete equations of motions and deformations of the object the explicit integration method was applied. The algorithm and application of 3D numerical analysis in ANSYS program were elaborated. This algorithm let for determination of influence of friction coefficient, initial yield stress and plastic hardening modulus. This factors influence will be carried out with 5 levels rotary experiment plan, which let for elaboration of regression equation to describe this relationship. Exemplary results of 3D numerical analysis of displacement and strain in thread for different conditions of rolling process are presented.

The increase of requirements concerning the accuracy of numerical analysis of technological processes with nonlinear contact such as drawing, cutting, embossing, burnishing rolling, thread rolling and machine cutting involves the extension of accuracy in determining workability parameters: initial yield stress σY0, plastic hardening modulus ET and true failure strain φf. Currently, those parameters are often determined in uniaxial tensile testing. Determination of the strain and stress states after the exceedance of ultimate tensile strength of the material, in the moment of stability loss (creation of the neck) constitutes the basic issue. Appearance of characteristic necking disturbs uniform, uniaxial state of stress. In the smallest intersection of the specimen there additionally appear radial stress and circumferential stress - three-dimensional state of stress is obtained. Currently used methods: Birdgman, Davidenkov-Spiridonova or Siebel do not allow calculating the values of those stress precisely enough. The paper concerns the new hybrid method of evaluating stress and strain states in the cylindrical specimen during of tension with the use of Finite Element Method (FEM).

In this study the process of burnishing rolling is considered as a geometrical and physical boundary and initial value problem, with unknown boundary conditions in the contact area. 3D dynamic explicit method for burnishing rolling process with taking into account surface after turning (as previous treatment) under ANSYS/LS-DYNA environment was established. The analysis covered surfaces characterized by vertical angles of the asperities in range: 60°÷150°. The simulation results (i.e. surface deformation, states of strain and stresses, depth of stress deposition) were evaluated. The influence of vertical angle of the asperities after turning process on the states of stress and strain and the depth of its deposition are presented.

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StreszczenieWstęp: Stres jest związany m.in. z wykonywaniem pracy w zawodach wysokiego ryzyka. Można go określić jako zespół reakcji wynikających z niedopasowania warunków i wymagań pracy do możliwości pracownika. Osoby różnie oceniające te obszary pracy mogą w różnym stopniu doświadczać stresu. Materiał i metody: Próba badawcza liczyła 128 funkcjonariuszy Straży Granicznej. Subiektywnej oceny obszarów pracy dokonano z zastosowaniem Kwestionariusza Obszary Życia Zawodowego (The Areas of Worklife Survey), a do badania nasilenia stresu użyto Skali Odczuwanego Stresu (Perceived Stress Scale -PSS-10). Wyniki: Wyłoniono 3 skupienia badanych istotnie różniących się w zakresie oceny wszystkich obszarów życia zawodowego. Przynależ-ność badanych do wyróżnionych skupień wyjaśnia 8% zmienności w zakresie nasilenia stresu. Z analizy regresji wynika, że oceny 3 obszarów życia zawodowego (poczucia kontroli, nagrody i obciążenie pracą) są istotnymi predyktorami nasilenia stresu odczuwanego przez funkcjonariuszy. Model okazał się istotny statystycznie -zmienne włączone do modelu wyjaśniają 19% zmienności zmiennej zależnej. Wnioski: Funkcjonariusze Straży Granicznej odmiennie oceniający obszary życia zawodowego różnią się w zakresie nasilenia odczuwanego stresu. Jest ono istotnie związane z możliwością podejmowania samodzielnych decyzji i zadowoleniem z nagród otrzymywanych za pracę. Znaczące jest też poczucie obciążenia pracą. Odczuwanie stresu przez funkcjonariuszy wiąże się głównie z oceną następujących obszarów pracy zawodowej: poczuciem kontroli, nagrodami i obciąże-niem pracą. Med. Pr. 2018;69(2):199-210 Słowa kluczowe: stres, miejsce pracy, zawody wysokiego ryzyka, stresory, obszary życia zawodowego, Straż Graniczna Abstract Background: Stress is associated with the performance of high-risk occupations. It can be defined as a set of reactions that results from mismatched working conditions and requirements to capabilities of an employee. People who differently assess these areas of work may experience varying degrees of stress. Material and Methods: The total of 128 Border Guard officers took part in the test. A subjective assessment of areas of work was made by using the Areas of Worklife Survey. The Perceived Stress Scale (PSS-10) was used to examine the severity of stress. Results: Three groups of examined people, differing significantly in the assessment of all areas of working life, were identified. Affiliation of the examined people to these groups explains 8% of the variability in the severity of stress. The results of the regression analysis allowed to consider the assessments of 3 areas of working life (control, rewards and workload) as important predicators of the severity of stress experienced by officers. The model turned out to be statistically significant, the variables included in the model explain 19% of the variability of the dependent variable. Conclusions:The officers who assess the areas of working life differently, differ in terms of severity of the experienced stress. The severity of stress is sig...

The shearing process such as the blanking of sheet metals has been used often to prepare workpieces for subsequent forming operations. The use of FEM simulation is increasing for investigation and optimizing the blanking process. In the current literature a blanking FEM simulations for the limited capability and large computational cost of the three dimensional (3D) analysis has been largely limited to two dimensional (2D) plane axis-symmetry problems. However, a significant progress in modelling which takes into account the influence of real material (e.g. microstructure of the material), physical and technological conditions can be obtained by using 3D numerical analysis methods in this area. The objective of this paper is to present 3D finite element analysis of the ductile fracture, strain distribution and stress in blanking process with the assumption geometrical and physical nonlinearities. The physical, mathematical and computer model of the process are elaborated. Dynamic effects, mechanical coupling, constitutive damage law and contact friction are taken into account. The application in ANSYS/LS-DYNA program is elaborated. The effect of the main process parameter a blanking clearance on the deformation of 1018 steel and quality of the blanks sheared edge is analyzed. The results of computer simulations can be used to forecasting quality of the final parts optimization.

Paper presents the modelling of the contact problem in the technological processes. Technological processes were considered as a geometrical and physical boundary and initial value problem, with unknown boundary conditions in the contact zone. An incremental model of the contact problem between movable rigid or elastic body (tool) and elastic/visco-plastic body (object) in updated Lagrange formulation, for spatial states (3D) was considered. The incremental functional of the total energy and variational, non-linear equation of motion and deformation of object on the typical step time were derived. This equation has been discretized by finite element method, and the system of discrete equations of motion of objects was received. For solution of these equations the explicit or implicit methods was used. The applications were developed in the ANSYS/LS-Dyna system, which makes possible a complex time analysis of the states of displacements, strains and stresses, in the workpieces in technological processes. Application of this method was showed for examples the modelling and the analysis of tensile test [1 and technological processes of metal forming [1-.