Permissible Stress Research Articles

Determining patterns of the vertical load on a covered wagon roof with a frame in the form of a triangular arch

The object of this paper is the processes of perception and redistribution of loads in the roof of a railroad covered wagon with a frame in the form of a triangular arch. To reduce the tare of the covered wagon, it is proposed to improve the structure of its roof. A feature of this improvement is that the roof frame is made in the form of a triangular arch with a reinforcing belt. This contributes to the reduction of the total mass of the roof compared to a typical structure. The selection of execution profiles of the beams forming the arch is carried out according to the maximum values of the moments that act in their cross-section. Taking into account the chosen profile of the arches, the calculation of the strength of the roof when it receives vertical loads was carried out. It was established that the strength of the roof under the considered load schemes is within the permissible stress values. Since the improvement of the roof structure contributes to the reduction of its weight by 1.8 % compared to the prototype, the movement of the covered wagon was evaluated under conditions of moving while empty. To this end, a mathematical modeling of the load of the covered wagon in the vertical plane during its movement along the joint unevenness was carried out. On the basis of the performed calculation, it was established that the movement of the wagon is assessed as "good". Special feature of the results is that the reduction of the tare of the supporting structure of the wagon was achieved by improving its roof, as the least loaded unit. The field of practical application of the results is railroad transport, including other areas of mechanical engineering. The conditions for the practical use of the results are a symmetrical roof load scheme in operation. The results of this research could contribute to advancements related to the design of modern structures of freight wagons with improved technical and economic indicators

Ensuring durability and reliability of contact rings of current collection devices when working in elastic-plastic state

The reliability of ring current-collecting devices during a given service life plays a decisive role in the opera- tion of power supply systems of various equipment and largely depends on the strength and reliability of all its components, in particular, contact rings. One of the most important characteristics of ring current collectors is the contact resistance, which is reduced by using non-ferrous and precious materials with low resistance, while increasing the downforce between the rings of the current collector. With an increase in the compression force F of the contact ring, the resistance of the contacts decreases to a certain minimum value and practically does not decrease with further growth of the force. The dependence of the contact resistance on the compression force has the form of a power function, the coefficients of which are determined experimentally. However, the operability of the contact rings in such severe conditions can be ensured in the case of low speeds and a small number of loading cycles by using the low-cycle fatigue area on the Weller curve. Having determined the coefficients of the equation of the inclined section on the Weller curve in the area of low-cycle fatigue, it is possible to determine the number of permissible loading cycles at a given stress level or solve the inverse problem of determining the permissible stress level if the number of loading cycles is known. To substantiate the correctness of the selected compressive force and the corresponding stresses, methods for calculating the fatigue margin coefficient, as well as a method for calculating the reliability of the ring material, are proposed. Reliability is estimated by the Gauss curve and is numerically expressed in the form of the probability of failure-free operation and the probability of failure, for which the corre- sponding theoretical dependencies are obtained. According to the proposed methods, calculations of the rings of the current-collection device used in EX- PRESS-type spacecraft were performed, which showed the operability of the methods and allowed to ensure the required service life of the contact rings and their reliability. A very simple analytical formulation of the methods allows us to solve both verification and design calculations of rings, depending on the task at hand.

Stability of Micro-Milling Tool Considering Tool Breakage

Micro-milling, widely employed across various fields, faces significant challenges due to the small diameter and limited stiffness of its tools, making the process highly susceptible to cutting chatter and premature tool breakage. Ensuring stable and safe cutting processes necessitates the prediction of chatter by considering the tool breakage. Crucially, the modal parameters of the spindle–holder–tool system are important prerequisites for such stability prediction. In this paper, the FRFs of the micro-milling tool are calculated by direct frequency response functions (FRFs) of the micro-milling cutter and cross-FRFs between a point on the shank and one on the tool tip. Additionally, by utilizing a cutting force model specific to micro-milling, the bending stress experienced by the tool is computed, and the tool breakage curve is subsequently determined based on the material’s permissible maximum allowable stress. The FRFs of the micro-milling tool, alongside the tool breakage curve, are then integrated to generate the final stability lobe diagrams (SLDs). The effectiveness and reliability of the proposed methodology are confirmed through a comprehensive series of numerical and experimental validations.

Rolling contact fatigue analysis of the soft zone for the main bearing in a tunnel boring machine

A hierarchical finite element modeling method is proposed to study the problem of fatigue spalling easily due to low hardness in the soft zone for the main bearing of a tunnel boring machine. Quasi-static analyses of the main bearing are performed based on the global symmetric model and verified by relative displacement tests of the rings. The invariant contact pressure is replaced by the rolling contact of the rollers in the local sub-model. The contact load is used as an input to solve the stress field, and then the effects of soft zone and hardened depth on the contact characteristics and fatigue lifetime of the sub-model are investigated. The results show there are stress peaks at the junction of the hardened and soft zones. The effect of hardened depth on the stress distribution and fatigue lifetime is relatively small. However, the optimum hardened depth is influenced by the contact load and the permissible stress of the material. The minimum lifetime of the raceway during rolling occurs in the soft zone. This paper achieves a fast and effective rolling contact fatigue analysis of the main bearing, which provides a theoretical basis for optimizing the main bearing design.

Effect of Geometry and Size of Fiber Reinforced Plastic Deck Profile on Behavior of Bridges

Due to the important role that bridges play in rescue operations after an earthquake, it is necessary that these structures have a higher level of protection against seismic attacks. Earthquake identifies the weak points of the structure and causes the most damage there. Bridges are very vulnerable to these attacks due to their low degree of uncertainty. All bridges built before 1971 were designed with the elastic design method (permissible stress). In this method, the effects of plasticity, section cracking, and plastic deformation are not taken into account. The change of seismic locations based on the principles of elastic design is much less. It is because the structure experiences in a real earthquake, one of the consequences of which is the falling of the decks due to the loss of the support surface. The decision to strengthen the bridge was made when there were many bending and shear cracks on the king beams. The bridge was created. The use of FRP profiles can significantly prevent the damage caused by corrosion and is a good alternative to the traditional methods of strengthening the structure. In this study, a design for the deck of a steel bridge with I beams is presented. The shape of reinforcement using FRP fibers with vinyl ester resins has also been investigated, the effect of the geometry of FRP profiles has been investigated. The presented specifications are optimized to obtain a lasting shape and section, especially for the pultrusion process. FRP materials are light, resistant to corrosion and have high tensile strength. These materials come in different forms and range from multi-layer factory sheets to dry sheets that can be twisted on various structural forms before adding resin, is available. The durability and high tensile strength of FRP materials are among the advantages of these materials. The durability and long-term performance of FRP requires more research, which is ongoing and continues.

Design and analysis of redundant electro-hydraulic-driven manipulator for tokamak vacuum vessel

Remote handling (RH), as one of the key technologies for fusion reactors in the future, has been the focus of research by researchers. This paper presents the design and analysis of a redundant manipulator with 10° of freedom (DOF) intended for use in vacuum vessel of the Tokamak. With a span of 3.15 m and a payload of 10 kg, the manipulator is powered by a combination of hydraulics and motors. The manipulator is mainly composed of the macro-operating arm, the micro-operating arm, and an end-effector, each serving its specific functions. This paper introduces and discusses the roles and capabilities of these components in the manipulation process. The finite element analysis (FEA) of the manipulator's structure reveals that the maximum stress of the structure is significantly lower than the permissible stress of the material Aluminium alloy 2A14. By utilizing the modified Denavit-Hartenberg (DH) method, the kinematic model was created, the forward kinematic matrix was established, and the workspace was analysed accordingly. The inverse kinematics solution was elaborated by the combination of geometric and numerical solutions. Given velocity and acceleration of the joints and the mass of the links, the force and torque of each joint were computed by the inward iterations method based on the Newton-Euler equation, and the rationality of the results was verified by ADAMS simulation. The results indicate that the manipulator, with sufficient strength and appropriate kinematic and dynamic properties, can fulfill the design objective and functional requirements.

Predicting soil parameters in Maroua 1st, Cameroon, using correlations of geophysical and geotechnical data

This study aims to predict specific soil parameters based on quantitative and qualitative correlations between electrical and geotechnical data. A total of 21 geotechnical boreholes followed by sampling, 21 light dynamic penetrometer tests, and 76 vertical electrical sounding surveys were carried out in Maroua 1st. The electrical resistivity data of the soil layers were obtained through 1D and 2D inversions of the ERT surveys. The geotechnical data were obtained from field tests and laboratory experiments. The statistical analysis of the entire dataset indicates that most of the samples are clay formations, as demonstrated by the means of variables and low variance coefficients, enabling qualitative identification. The distribution analysis of the parameters confirms the complexity of the physical characteristics of soils and the measurement procedures for each parameter. The Spearman's rank correlation matrix indicates that these observations can be used to propose predictive models for free swelling, allowable stress, natural water content, and electrical resistivity. Correlations between free swelling (εg) and other variables are not significant, as the degree of significance is lower than the fixed limit, except for models εg - W (R2 = 0.94), εg - ρ (Ώ.m) (R2 = 0.803), and εg - σ adm (R2 = 0.757). Grouping variables in multiple linear regression enables the development of a mathematical model. The predicted values of εg from this model demonstrate good agreement with the measured values for a validity domain of 0–16 %. The soil's natural water content has a strong correlation (R2 = 0.80 and rs = – 0.87) with electrical resistivity, meaning that an increase in water content results in a decrease in electrical resistivity. The permissible stress σadm has a strong correlation (R2 = 0.89 and rs = 0.85) with electrical resistivity. This indicates that changes in soil electrical resistivity are associated with soil stiffness.

Biomechanical characteristics of Sanders type II and III calcaneal fractures fixed by open reduction and internal fixation and percutaneous minimally invasive fixation

BackgroundThis work investigated the differences in the biomechanical properties of open reduction and internal fixation (ORIF) and percutaneous minimally invasive fixation (PMIF) for the fixation of calcaneal fractures (Sanders type II and III calcaneal fractures as examples) through finite element analysis.MethodsBased on CT images of the human foot and ankle, according to the principle of three-point fixation, namely the sustentaculum tali, the anterior process and the calcaneal tuberosity were fixed. Three-dimensional finite element models of Sanders type II and III calcaneal fractures fixed by ORIF and PMIF were established. The proximal surfaces of the tibia, fibula and soft tissue were constrained, and ground reaction force and Achilles tendon force loads were added to simulate balanced standing.ResultsThe maximum stress was 80.54, 211.59 and 113.88 MPa for the calcaneus, screws and plates in the ORIF group and 70.02 and 209.46 MPa for the calcaneus and screws in the PMIF group, respectively; the maximum displacement was 0.26, 0.21 and 0.12 mm for the calcaneus, screws and plates in the ORIF group and 0.20 and 0.14 mm for the calcaneus and screws in the PMIF group, respectively. The values obtained from the simulation were within the permissible stress and elastic deformation range of the materials used in the model, and there was no significant stress concentration. The maximum stress and displacement of the calcaneus and implants were slightly lower in the PMIF group than in the ORIF group when fixing Sanders type II and III calcaneal fractures.ConclusionsThis study may provide a reference for optimising the design of implants, the development of individualised preoperative plans and the choice of clinical surgical approach.

Practical Fatigue Strength Diagrams for Compression Springs Based on the FKM-Guideline “Analytic Strength Assessment for Springs“

Today’s helical compression springs are designed according to DIN EN 13906-1. The fatigue diagrams contained there are outdated and essential influences on fatigue strength are not taken into account. In order to resolve these circumstances, endurable stresses were calculated with the FKM guideline “Analytic Strength Assessment for Springs and Spring Elements”, which was published in 2020. The application of the included safety concept results in characteristic curves for permissible stresses that are conservative with regard to real test data. Therefore, the new fatigue strength diagrams can be used directly for standard applications. This article gives an overview of the method and accompanying experiments. The presented results enable spring designers to design competitive springs in a shorter time and with less testing effort according to the current state of research.

РАСЧЁТ НА ПРОЧНОСТЬ И ПРОВЕРКА ЖЁСТКОСТИ СТАТИЧЕСКИ ОПРЕДЕЛИМОЙ БАЛКИ ДВУТАВРОВОГО СЕЧЕНИЯ

This paper presents a strength calculation for a statically determinate I-beam. Diagrams of internal force factors (transverse forces and bending moments) are constructed and the number of the I-beam is selected according to the given external load and the values of the material strength characteristics. The given material characteristics are permissible normal stress, elastic modulus and permissible shear stress. The strength of a beam with a selected cross-section for shear stresses was tested. To construct the I-beam elastic line, the deflections of cross-sections with a unit interval along the length are calculated. The beam deflections were calculated using the universal elastic line equation. The obtained value of the maximum beam deflection made it possible to draw a conclusion about the beam sufficient hardness and operability under given external loads.

Calculation of the risk of destruction of the pavement by permissible stresses in monolithic layers

Calculation of the risk of destruction of the pavement by permissible stresses in monolithic layers

Finite Element Method Analysis of Potential Shaft Breakage in Truck Wheel Drive Due to Initial Crack

The need for truck transportation in the city of Langsa is increasing. This is because the residents of Langsa use trucks as a means of transporting palm oil from plantations. Engine component failures are often experienced in every mechanical construction, and these failures are marked by the breaking of these engine components. Cracks become one of the potential sources of failure in the machine structure. There is a need to detect cracks in the shaft at an early stage to prevent damage. Therefore, it should be investigated using appropriate techniques at the early stage of crack formation. The purpose of this research is to find the potential source of shaft fracture relative to the initial crack location on the shaft. This research method is carried out by determining the same initial crack dimensions at two different locations. The initial crack locations are determined through a case study of frequent fractures in the fillet spline and fillet flange locations. The calculation results show that the permissible stress of the shaft is 80.7 MPa. The finite element method simulation results show that the maximum shear stress value on the shaft without an initial crack is 65.234 MPa, on the shaft with an initial crack in the fillet spline location is 69.654 MPa, and on the shaft with an initial crack in the fillet flange location is 78.79 MPa. The finite element method simulation results also show that the von Mises shear stress value on the shaft without an initial crack is 113.29 MPa, on the shaft with an initial crack in the fillet spline location is 120.66 MPa, and on the shaft with an initial crack in the fillet flange location is 137.23 MPa. The finite element method simulation results further show that the von Mises shear strain value on the shaft without an initial crack is 0.000567, on the shaft with an initial crack in the fillet spline location is 0.000630, and on the shaft with an initial crack in the fillet flange location is 0.000693. In conclusion, the potential source of failure experienced by the shaft between the two locations of frequent failure is the shaft with an initial crack in the fillet flange location.

Construction Design of the Floater Considering the Free-Falling Impact of the Floatplane on Calm Water

The floatplane-type aircraft is very suitable to be developed as a means of transportation connecting the scattered islands in Indonesia, as it has floats under the fuselage to make landings and operate on the water surface. In bad weather, a floatplane can lose lift, resulting in a free fall from an abnormal height and a violent collision between the floatplane structure and the water surface. Meanwhile, regulations require that the strength of the structure be able to withstand the impact load due to an emergency landing. This paper proposes a floater construction design for the N219 floatplane with three scantling variations of 5083 H321 aluminium material that considers the total payload and take-off weight. The magnitude of the impact load on the bottom of the float with the water surface in the case of free fall at 0.5 m and 1 m height is predicted by the Wegner equation model at each cross section along the float. The magnitude of stress in each floater construction design is evaluated by the principle of the finite element method using commercial software. The simulation results show that all models have a maximum stress less than permissible stress and also maximum deformation is unsignificant.

Investigation of the influence of an intermediate adapter on the dynamic load of a supporting structure of a platform wagon

Summary: This article is focused on a presentation of the results of the theoretical justification of the use of an intermediate adapter placed between the main supporting structure of a platform wagon and the cargo. Such a decision will contribute to reducing the vertical load of both the supporting structure of a platform wagon and ensuring the safety of the cargo transported on it. The mathematical modelling of the vertical load of a platform wagon supporting structure when moving along the joint unevenness of the track was carried out to substantiate the use of the designed intermediate adapter. In this regard, a corresponding mathematical model was created. There is taken into account an oscillating system consisting of four bodies: the platform wagon supporting structure, two bogies (the 18–100 model) and the cargo. At the same time, the cargo is considered up to the full carrying capacity of the platform wagon. The track is considered elastic-viscous. The mathematical model was solved in the MathCad software. The initial conditions (displacement and velocities) are set to be close to zero. The results of the solution established that the accelerations acting on the platform wagon supporting structure are reduced by 8.4 % compared to those acting on the typical structure without the designed intermediate adapter. The acceleration acting on the cargo placed on the platform wagon frame is 11.9 % lower in comparison with the standard load perception scheme.
 The strength analysis of the adapter was calculated considering the determined values of the accelerations. At the same time, the finite element method was used for the strength analysis of the adapter in the SolidWorks Simulation software. It was determined that the calculated maximum stresses in the adapter structure are 4.1 % lower than permissible stress values. Therefore, the strength condition of the adapter is met. The performed research will contribute to a creation of developments in the design of modern designs of railway vehicles

Parametric Study of Additional Temperature Stresses in Continuously Welded Rails on Steel Truss Railway Bridges

Additional temperature stresses in continuously welded rails (CWRs) are caused by track/bridge interaction (TBI) due to thermal actions. Exceeding permissible stresses in CWRs on the bridge can lead to track buckling or rail cracking, compromising the safety of railway traffic. The main aim of the conducted study is to determine the effects of the key parameters such as rail cross-sectional area, track longitudinal resistance, bridge expansion length, and longitudinal stiffness of the fixed bridge support on the reduction of additional temperature stresses in CWRs on steel truss railway bridges. To quantify the effects of these parameters, two steel railway bridges with CWRs and the maximum expansion lengths according to UIC Code 774-3 were analyzed: (1) simply supported truss bridge with expansion length of 60 m and (2) continuous truss bridge with expansion lengths of 2 × 60 m. According to the obtained results, the track longitudinal resistance had the most significant impact on additional temperature stresses in CWRs, leading to their reduction of up to 72%. The bridge expansion length and the rail cross-sectional area led to reductions of up to 25% and up to 18%, respectively. Considering the deformation criteria of TBI, the longitudinal stiffness of the fixed bridge support had a minor effect on the reduction of additional temperature stresses in CWRs.

The Effects of Seawater Treatment on Selected Coniferous Wood Types.

The mechanical strength of wood from Scots pine (Pinus sylvestris), European larch (Larix decidua), and Norway spruce (Picea abies) was studied using static compression tests. The material was exposed under constant soaking in water with salinity of 7‱. The liquid mix was prepared according to a value roughly equivalent to the average salinity along the entire length of the Baltic Sea. The mechanical strength and quality of the raw material were determined using a sea salt saturation test, which determined the adhesion of the raw material to the extrusion process (permissible stress). An investigation was conducted to determine the physicochemical parameters of the material that was tested. It was investigated how much mineral compounds were absorbed over four cycles lasting a total of six weeks during the test. According to the statistical analysis, the chemical composition of wood and the presence of salts and mineral compounds correlated with its mechanical strength. An important part of the study focused on examining the factors affecting the construction of coniferous wood structures. The preparation of the raw material correctly can provide information on how the material can be protected during exposure to specific environmental conditions for longer.

Depth effect of tropical heavy hardwood of kekatong species towards EC5 using Weibull’s theory

The design practice has shifted from permissible stress design to limit state design using Eurocode 5 (EC5), which introduces design strength optimization. However, the adoption of EC5 in Malaysia cannot be done directly due to the absence of design strength data for Malaysian timber species. This paper presents a study that evaluates the bending strength properties, moisture content, and density of kekatong (Cynometra malaccensis) timber specimens using the Weibull theory to produce 1/k values for the local timber species. The depth impact adjustment factors for kekatong timber had a value of 0.23, which is not far from the well-established 1/k value of 0.2 for softwood and temperate hardwood with characteristic densities below 700 kg/m3 in EC5. The study shows that the bending strength of local timber is affected by its volume, and the variation of bending strength at several probabilities is in close agreement with theoretical predictions. Overall, the study provides important insights for the design of timber structures using Malaysian timber species, which can be used to improve the safety and sustainability of timber structures.

Modelling and Analysis of Expansion Joints' Effect on Dynamic Performance of Railway Rigid Overhead System.

This study focuses on developing a comprehensive model of a rigid overhead system, which includes essential components such as the suspension structure, positioning clamp, and expansion joint. The modelling approach utilizes finite element theory and beam elements to accurately represent the displacement, stiffness, and mass characteristics of the system. The models also incorporate the suspension structure and positioning line clamp, which play crucial roles in suspending and positioning the busbar. Various suspension structures and positioning line clamps are evaluated based on their dynamic characteristics. The expansion joint, responsible for connecting different anchor sections of the rigid overhead system, undergoes a detailed analysis. Different assembly scenarios, including ideal and deflected assembly conditions, are considered. To simulate the dynamic behaviour of the expansion joint, additional beams are introduced into the system model. The primary finding of the analysis is that the maximum stresses observed in the constructed expansion joint model, under different temperature conditions and normal/deflected assembly conditions, remain within the permissible stress limits of the material. This indicates a high level of safety. However, certain areas exhibit stress concentration, particularly at the sliding block B and sliding rod A positions. This stress concentration is primarily attributed to the unique assembly form of the expansion joint. To improve stress distribution and enhance service reliability, the analysis suggests optimizing the installation deflection angle and geometric design of the expansion joint. Furthermore, the concentrated mass at the expansion joint significantly impacts the current collection quality of the pantograph-overhead system. Mitigating this negative impact can be achieved by reducing the mass of the expansion joint.

Study of mechanical properties of cylinder under transient multi-physical field coupling conditions

The use of lightweight metal cylinders is of great significance to artillery weapon systems in terms of significant mass reduction, service life extension, power consumption reduction and operational effectiveness. Based on the load conditions provided by the classical internal ballistic theory, a high precision finite element model is solved by the explicit integration algorithm with central difference. The results show that the maximum stress of the thin-walled cylinder increases linearly with the increase of the initial clearance, while the maximum extraction force increases first and then decreases, while the influence of temperature on the extraction force cannot be ignored. Therefore, the design of the initial gap between the thin-walled cylinder and the thick-walled cylinder should be designed to ensure that the maximum stress of the thin-walled cylinder does not exceed the maximum permissible stress and to meet the minimum extraction force, while choosing the correct extraction timing can effectively reduce the extraction force.

Structural Design of the Substructure of a 10 MW Floating Offshore Wind Turbine System Using Dominant Load Parameters

Fully coupled integrated load analyses (ILAs) to evaluate not only the load response but also the structural integrity are required to design a floating offshore wind turbine, since there has been no firmly established approach for obtaining the structural responses of a FOWT substructure in the time domain. This study aimed to explore if a direct strength analysis (DSA) technique that has been widely used for ships and offshore structures can adequately evaluate the FOWT substructure. In this study, acceleration and nacelle thrust were used for the dominant load parameters for DSA. The turbine thrust corresponding to the 50-year return period was taken from the literature. The acceleration response amplitude operator (RAO) was obtained through frequency response hydrodynamic analysis. The short-term sea states defined by the wave scatter diagram (WSD) of the expected installation area was represented by the JONSWAP wave spectrum. To account for the multi-directionality of the short-crested waves, the 0th order moments of the wave spectrum were corrected. The probabilities of each short-term sea state and each wave incidence angle were applied to derive the long-term acceleration for each return period. DSA cases were generated by combining the long-term acceleration and nacelle thrust to maximize the forces in the surge, sway, and heave directions. Linear spring elements were placed under the three outer columns of the substructure to provide soft constraints for hive, roll, and pitch motions. Nonlinear spring elements with initial tension were placed on the three fairlead chain stoppers (FCSs) to simulate the station-keeping ability of the mooring lines; they provided initial tension in the slacked position and an increased tension in the taut position. The structural strength evaluation of the coarse mesh finite element model with an element size same as the stiffener spacing showed that high stresses exceeding the permissible stresses occurred in the unstable members of the substructure. The high stress areas were re-evaluated using a fine mesh finite element model with an element size of 50 mm × 50 mm. The scope of structural reinforcement was identified from the fine mesh analyses. It was found that the DSA can be properly utilized for the substructure strength assessment of a FOWT.