Annals of the „Constantin Brâncu și” University of Târgu-Jiu,Engineering Series, Issue 4/2014 226 USING BRINELL HARDWARE METHOD FOR EVALUATION OF RESIDUAL LIFETIME OF MINING EQUIPMENT -I Drd. Vâlceanu Florin, Popeci Heavy Equipment, Târgu-Jiu subs., ROMANIA Prof. Cătălin Iancu, Constantin Brâncuşi University of Târgu-Jiu, ROMANIA ABSTRACT: In this paperwork is proposed, by using HB hardness of bearing elements, a method of evaluation of residual lifetime of mining equipment. Thus, by correlating the ε – N method, based on plastic deformation, which represents the cause of initiation of Fatigue cracks, and specific methods of Fracture mechanics, which give the information regarding the evolution of initiated cracks and the propagations during work cycles, it can be estimated the residual lifetime, without affecting the safety of equipment. KEY WORDS: HB hardness, residual lifetime, mining equipment. 1. INTRODUCTION Metal fatigue is a process that leads to a premature rupture or damage to the parts subjected to repeated stresses. Fatigue is the predominant mode of loss of structural integrity, important both in frequency and as a decisive factor in determining the working stresses of the parts subjected to fluctuating loads. Understanding the physical mechanisms of fatigue damage, especially the behavior of short cracks, allows the study of factors influencing the fatigue limit and fatigue life: corrosive environment, fretting, surface treatments, material grain, medium stresses level, multiaxial tensions, fluctuating loads, metal’s hardness and their combined action. The purpose of this paper is to present a non- destructive method used in determining the number of working cycles of mining equipment, but also for other equipment. Such method is based on determination of hardness in areas of high mechanical stress intensity of all required support structures, correlating yield strength and Brinell hardness of the material, the method being developed and proposed by Roessle-Fatemi and Muralidharan-Manson. On the other hand in the breaking zone of a specimen, measuring hardness is observed that it is much larger than in other area of the specimen subjected to tensile, as seen in figure 1. Figure 1. Specimens subject to traction There are currently three different methodologies for calculating fatigue, which correspond to three "theories" distinct approaches.
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Annals of the „Constantin Brâncuși” University of Târgu-Jiu,Engineering Series, Issue 4/2014
226
USING BRINELL HARDWARE METHOD FOR EVALUATION OF RESIDUAL LIFETIME OF MINING EQUIPMENT -I
Drd. Vâlceanu Florin, Popeci Heavy Equipment, Târgu-Jiu subs., ROMANIA Prof. Cătălin Iancu, Constantin Brâncuşi University of Târgu-Jiu, ROMANIA
ABSTRACT: In this paperwork is proposed, by using HB hardness of bearing elements, a method of evaluation of residual lifetime of mining equipment. Thus, by correlating the ε – N method, based on plastic deformation, which represents the cause of initiation of Fatigue cracks, and specific methods of Fracture mechanics, which give the information regarding the evolution of initiated cracks and the propagations during work cycles, it can be estimated the residual lifetime, without affecting the safety of equipment. KEY WORDS: HB hardness, residual lifetime, mining equipment.
1. INTRODUCTION Metal fatigue is a process that leads to a premature rupture or damage to the parts subjected to repeated stresses. Fatigue is the predominant mode of loss of structural integrity, important both in frequency and as a decisive factor in determining the working stresses of the parts subjected to fluctuating loads. Understanding the physical mechanisms of fatigue damage, especially the behavior of short cracks, allows the study of factors influencing the fatigue limit and fatigue life: corrosive environment, fretting, surface treatments, material grain, medium stresses level, multiaxial tensions, fluctuating loads, metal’s hardness and their combined action.
The purpose of this paper is to present a non-destructive method used in determining the number of working cycles of mining equipment, but also for other equipment. Such method is based on determination of hardness in areas of high mechanical stress intensity of all required support structures, correlating yield strength and Brinell hardness of the material, the method being developed and proposed by Roessle-Fatemi and Muralidharan-Manson. On the other hand in the breaking zone of a specimen, measuring hardness is observed that it is much larger than in other area of the specimen subjected to tensile, as seen in figure 1.
Figure 1. Specimens subject to traction
There are currently three different methodologies for calculating fatigue, which
correspond to three "theories" distinct approaches.
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a. Method σ - N Method based on stress analysis is used to calculate the unlimited durability. Primary experimental data are in the form of sustainability charts, with coordinates "maximum stress - number of cycles to failure" (Wöhler curve). Failure is defined by the total separation of the two parts of the tested specimen. Method σ - N is for parts without cracks, specimen-like shapes (rotating bending test) and having comparable size, usually made of steel or ferrous metals. b. Method ε − N Datele experimentale primare se prezintă sub formă de diagrame la durabilitate mică, în coordonate “deformaţie specifică ciclică - număr de cicluri până la cedare” (curba Coffin-Manson), determinate prin încercări de amplitudine constantă, pe epruvete solicitate axial. Method based on the analysis of specific strains is used to calculate the limited
durability. It is applicable to parts without initial cracks, subjected under elastic-plastic loads, usually made of forged steel or materials without defects. Primary experimental data are in the form of charts at low sustainability, with coordinates "specific cyclic deformation - number of cycles to failure" (Coffin-Manson curve) caused by constant amplitude tests on specimens axial stressed. c. Fault tolerance method Crack propagation analysis method is applicable on parts with initial cracks (usually welded or riveted structures). In this case, the stress singularity at the crack tip sizes require the use of Fracture mechanics. The advantages of using computational fracture mechanics relationships is that they can show the evolution of cracks and size that can be reached after a certain number of cycles.
2. NONDESTRUCTIVE MEASUREMENTS In figure 2. is shown where measurements
were made, on upright and diagonal elements, measurements made in two distinct areas top and bottom, for each element.
Figure 2. Places of measurements
Measurements were carried out in each node of the mounting area and diagonals on both
walls, left – right on the elements considered, namely pillars and diagonals.
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Before making measurements, the surface (place) where the measurement took place was machined. In figure 3. can be seen technological
operations performed in order to determine the hardness of the elements considered, the points where the hardness was measured and the processing on the work surface.
Figure 3. Machined zone of the element
After preparing the bearing elements as shown, it was done the hardness measurement on diagonals and pillars, as shown in Figure
3. In Table 1 are shown photos of hardness measurement areas on the supports.
Table 1. Pictures of zones for taking hardness measurements
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3. ANALYSIS OF HARDNESS DISTRIBUTION
In figure 4 is presented the geometric system of right subassembly, and in table 2 are
registered the hardness values measured in nodes of diagonals and pillars.
Figure 8. Hardness distribution – top side (left subassembly)
Figure 9. Hardness distribution – top side (left subassembly)
4. CONCLUSIONS The hardness measuring method is a method easily applied in estimating the life of a machine or equipment, by the relative simplicity of the sampling;
This method gives information on local events that occurred in that area, thus the points where there has been a large increase in hardness was a local hardening which signify an important local deformation. It may be noticed in the chart of Hardness distribution – top side
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(left subassembly) the N02` node, where otherwise is noted the deformation of the upper beam and vertical pillar. To determine the approximate lifespan the hardness measuring method must be correlated with fracture mechanics methods. REFERENCES [1]. ASTM E466-07. Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials, Annual Book of Standard, ASTM International, www.astm.org., West Conshohocken, PA, USA, 2007. [2]. ASTM E468-04. Standard Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials, Annual Book of Standard, ASTM International, www.astm.org., West Conshohocken, PA, USA, 2004.
[3]. ASTM E739-91. Standard Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data, Annual Book of Standard, ASTM International, www.astm.org., West Conshohocken, PA, USA, 2004. [4]. Atkinson, H., & Anderson, C., Estimation of the Maximum Inclusion in Clean Steels and the Relationship with Mechanical Properties. Dept. of Mechanical Engineering, University of Sheffield, Sheffield, South Yorkshire, England, 2003. [5]. Chad M. Poeppelman, Axial and Torsion Fatigue of High Hardness Steels, University of Toledo, Ohio, USA, 2011. [6]. Roessle, M. L., Fatemi, F., Strain-controlled fatigue properties of steels and some simple approximations, Int. J. Fatigue 22, 495–511, 2000. [7]. Ralph I. Stephens, Ali Fatemi, Robert R. Stephens, Henry O. Fuchs, Metal Fatigue in Engineering, ISBN 978-0-471-51059-8, Wiley, 2000.