PROCEEDINGS OF THE INSTITUTE OF VEHICLES 3(103)/2015

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1 PROCEEDINGS OF THE INSTITUTE OF VEHICLES 3(103)/2015 Miroslav Blatnický 1, Ján Dižo 2 DESIGN AND ANALYSIS OF HYDRAULIC ARM OF LIGHT VEHICLE 1. Introduction An important role of engineers is to analyse the existing and newly-designed working processes in order to find an optimal way of executing the given operation. The best working process is generally considered the one that minimises the cost of performance, which can be achieved by mechanisation. Mechanisation is an important means of increasing productivity, quality and production competitiveness. Successful introduction of mechanisation requires knowledge and understanding of physical dependencies of executed operations. Operations are executed by transfer of mechanical, electrical, pneumatic or hydraulic energy. The aim is that individual working processes be as short and simple as possible, easy to learn and at the same time require minimum man-power deployment. Mechanisation significantly relieves people of hard physical work for instance in dangerous or harmful environment. Such a means of mechanisation utilisable not only in transport is the designed hydraulic arm [2], which significantly simplifies manipulation with great operativeness. With the requirement of minimum production costs we reach the most gainful output/costs ratio. 2. Design of arm geometry Every transport and handling machine consists of three main parts: - steel structure, - driving mechanisms, and - other parts (e.g. cab, steps, etc.). The aim of this work is to design a hydraulic arm steel structure to be mounted on a particular light goods vehicle (Fig. 1). The whole mechanism consists of three parts of steel structure. The advantage of this solution is that the operator needs driving license only for vehicles with total mass up to 3500 kg. In previous functional calculations [2], force effects on the arm were detected (Fig. 2) during operation due to the load with mass of 300 kg. Consequently, analytical dimensional calculation was executed and all dimensions of the arm were designed [2]. Designed lengths of individual parts, resulting from construction of hydraulic cylinders in Figure 2, are as follows: c 1 = mm, c 2 = mm, c 3 = mm, e 1 = e 2 = e 3 = 75 mm, a 1 = a 2 = 210 mm, b 1 = 774 mm. Calculated inner force effects of the mechanism in Fig. 1 are: F z = 2943 N, F v1 = 45,126 N, R Ax = 45,126 N, 1 Eng. Miroslav Blatnický, PhD, Faculty of Mechanical Engineering, University of Žilina, Slovakia, miroslav.blatnicky@fstroj.uniza.sk 2 M.Sc Eng. Ján Dižo, PhD, Faculty of Mechanical Engineering, University of Žilina, Slovakia 5

2 R Ay = 2943 N, β = , F v2 = 30,710 N, R Bx = 5824 N, R By = 27,210 N, R Cy = 2943 N. Fig. 1. Platform for the designed arm Fig. 2. Free diagram of arm Fig. 3. Lifting pivot arm with pick-up bed 6

After defining the cross-section dimensions by analytical calculation, it is possible to build a 3D model of the hydraulic arm (Fig. 3) in CAD software Catia.

3 After defining the cross-section dimensions by analytical calculation, it is possible to build a 3D model of the hydraulic arm (Fig. 3) in CAD software Catia. The whole arm consists of three parts and to simplify the problem, numerical analysis of each part of the arm is made separately. In this paper, the analysis of the middle part of the arm is carried out using the FEM software ADINA. The 3D model of the middle part is shown in Figure 4. Fig. 4. 3D model of the middle part of the arm 3. Analytical calculation For the safety of the construction is chosen safety factor k = 1.5 (-). In production of steel construction a material STN was chosen, because of its suitable mechanical properties, guaranteed weldability and relatively low cost. Normalised hot drawn square seamless steel tubes were chosen. Provisionally, it is chosen profile TR4 HR 120x100x STN Allowed combined loading of the steel construction with consideration of the safety factor is σ red dov = 120 MPa. To determine a value of stress in the middle part of the arm, an analytical calculation by classic theory of elasticity and strength is carried out. The body considering as a beam with exact geometry and load, which value was solved in the previous step. Calculation of the bending moment as a dominant loading is carried out by method of virtual cut. The beam is cut as many times as it is divided by outer loading, inner loading and by geometry, i.e. three times (fig. 5). Fig. 5. Courses of moments and normal forces In critical section, besides bending stress also tensile stress from normal force F N = N acts. The total stress then is (1): (1) 7

4 By solving the equation (1), we get a value of total stress σ c = 73.8 MPa. Force from the hydro motor F V1 then loads the critical section through holder by shear stress parallel with the length of the construction and force from the hydro motor F V2 loads the critical section through the holder also by shear stress, but perpendicular to the length of the construction. Value of the resultant shear stress is found out from the equation (2): (2) The resultant shear stress in the critical section then is τ s = 9 MPa. Effective stress in the critical section is calculated according to HMH hypothesis (3): Value of the effective stress in a weld reaches by analytical method of calculation σ RED = 75,5 MPa. However, value of the resultant stress will grow because of nonconsidering of. 4. Building the model by shell elements The FEM software ADINA was used to calculate stress distribution in the structure. The ADINA software allows simulating various problems of mechanics including statics, dynamics, contact, etc. [1]. (3) Fig. 6. Mesh and boundary conditions of the construction Firstly, it is necessary to create geometry. The arm under consideration (Fig. 6) is made of normalised square seamless steel tube and therefore it is convenient to model it using shell elements. 8

When the model is created, boundary conditions can be entered into the software. Loading of the arm is realised by a couple of forces at the end of the arm in its most efficient position.

The second joint is pin connection between the arm and the eye of the hydraulic cylinder that commands the movement of this part (Fig. 7)

5 When the model is created, boundary conditions can be entered into the software. Loading of the arm is realised by a couple of forces at the end of the arm in its most efficient position. Gripping of the construction is by two rotational joints. One rotational joint features pin connection between the third and second part of the arm. The second joint is pin connection between the arm and the eye of the hydraulic cylinder that commands the movement of this part (Fig. 7). Fig. 7. Given boundary conditions Entering the boundary conditions is followed by the model meshing. To create the mesh, we used four-node linear tetrahedral elements with mesh density 5 mm. Figure 8 shows the arm after meshing. Fig. 8. Detail of the mesh used Figure 8 shows detail of the mesh in the pin hole site. The maximum stress according to the analytical calculation is 75,5 MPa. This value was determined without considering the own weight of the arm. It means that the maximum stress in the arm can increase in numerical analysis when the arm own weight is taken into consideration. The 9

Figure 9 shows displacement of the arm due to the load during at the machine operation. The software states maximum displacement by 0.5893 mm.

6 chosen profile TR4 HR 120x100x6 made of steel has admissible effective stress 120 MPa within the safety factor (Blatnický et al. 2014). Meshing the model is followed by numerical calculation and then we can show the results of required quantities in a post processor. Figure 9 shows displacement of the arm due to the load during at the machine operation. The software states maximum displacement by mm. The maximum admissible deflection is up to 1/600 of the entire length. If the total length of the arm is mm, then the admissible deflection is 1.92 mm, which is more than the determined value of mm. This means that displacements in the structure are within admissible values. Fig. 9. Simulated displacement of the arm part The next important determined values are distribution of stress in the structure, determination of critical point in the structure and the maximum stress in the critical point of the structure [3]. If the maximum stress value is under the specified admissible stress of 120 MPa, then it is well dimensioned and no further optimisation of the structure is needed. Fig. 10. Distribution of effective von Misses stress 10

Figure 10 shows distribution of effective von Mises stress in the middle part of the arm. Correctness of the analytical solution was verified by numerical analysis.

It is clear that the value is below the design value of 120 MPa, and therefore the conclusion is that the structure with such geometry endures the load.

7 Figure 10 shows distribution of effective von Mises stress in the middle part of the arm. Correctness of the analytical solution was verified by numerical analysis. The maximum simulated stress value is 84,66 MPa. It is clear that the value is below the design value of 120 MPa, and therefore the conclusion is that the structure with such geometry endures the load. The critical section is shown in Figure 11. As the resultanting stress is lower than admissible stress, we can conclude that the designed structure will be safe. Safety is the most important requirement posed on any structure [4]. Fig. 11. Detail of the critical section in the arm Fig D model of the arm construction 11

8 5. Summary As the aim of the paper was calculation of the middle part of the hydraulic arm steel structure, it can be said that the aim was achieved. The designed arm part in operation endures working with the load for which it was dimensioned. To guarantee the structure safety requires execution of numerical analysis of other parts of the arm as well (Fig. 12). Numerical analysis and optimisation of all parts of the arm is followed by the next step in solving this issue - building a model of the structure in MBS software. The aim of this analysis is to simulate dynamic effects of the load in the mechanism operation. Acknowledgement This contribution is the result of the project implementation: Modern methods of teaching of control and diagnostic systems of engine vehicles, ITMS code , supported by the Operational Programme Education. References [1] Bathe, K.J Finite element procedures. Prenice-Hall, Inc. New Jersey ISBN [2] Blatnický, M. &Dižo, J The designed functional calculation of the hydraulic arm of a track maintenance machine to lift of piece loads. (Online). In: Railway transport and logistics. Scientific and technical on-line journal. (In Slovak), 2/2014, Žilina ISSN , Pp [3] Harušinec, J., Gerlici, J., Lack, T Stress conditions in the contact of rail wheel tread and rail head. (In Slovak). In: Dynamics of rigid and deformable bodies 2008: Proceedings, VI. International conference:ústí nad Labem, October 17 th 19 th. ISBN , Pp [4] Harušinec, J., Gerlici, J., Lack, T A rail/wheel contact analysis with the help of the Finite element method. (In Slovak). In: PRORAIL 2007: XVII. International conference Current Problems in Rail Vehicles, Žilina 2007, September 19 th 21st, Slovak Republic, Proceedings, Scientific and technical Society at the University of Žilina. ISBN , Pp Abstract The paper deals with numerical analysis of the middle part of the designed hydraulic arm. The arm is used for manipulation of load pieces up to 300 kg. Its load capacity depends on the transport vehicle to be placed on - vehicle type Pick-up. Great operability of this mechanism predetermines its wide application in construction, transport, business, etc. Locations and values of the maximum stress in the first part of the structure are calculated using the ADINA software. These results determine the relevant data necessary for correct design and functioning of the machine. After carrying out all the analyses and calculations we will be able to determine the safe use of the machine and put it into operation. Safety is the most important requirement in any structure operation. 12

9 Key words: Hydraulic arm, FEM simulation, calculation PROJEKTOWANIE I ANALIZA HYDRAULICZNEGO RAMIENIA DLA LEKKICH SAMOCHODÓW Streszczenie Referat przedstawia analizę numeryczną środkowej części projektowanego ramienia hydraulicznego. Ramię służy do podnoszenia ciężarów o wadze do 300 kg. Maksymalna nośność zależy od pojazdu transportowego, w którym zabudowano ramię, w tym przypadku jest to pojazd typu pick-up. Świetna funkcjonalność tego mechanizmu determinuje jego szerokie zastosowanie w budownictwie, transporcie, biznesie itp Miejsca i wartości maksymalnych naprężeń w pierwszej części konstrukcji są obliczane za pomocą programu ADINA. Wyniki te określają odpowiednie dane niezbędne do prawidłowej konstrukcji i działania maszyny. Po przeprowadzeniu wszystkich analiz i obliczeń będziemy w stanie określić, parametry bezpiecznego korzystania z urządzenia i je przetestować w pracy. Bezpieczeństwo jest najważniejszym wymogiem w projektowaniu takiej konstrukcji. Słowa kluczowe: ramię hydrauliczne, symulacje MES, obliczenia 13

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