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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 4. Geometric system - right subassembly

Table 2. Hardness values - right subassembly

Node Hardness values [HB] Average

N01 110 119 106 106 111 110.4 N02 143 141 151 107 135 135.4 N03 144 143 157 144 172 152 N04 120 114 101 106 110 110.2 N05 128 119 124 125 124 124 N06 102 101 99 98 106 101.2 N07 154 144 150 166 154 153.6 N08 155 158 161 153 163 158 N11 130 124 128 121 137 128

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N12 146 150 181 162 153 158.4 N13 121 116 114 111 114 115.2 N14 109 109 108 106 110 108.4 N15 136 129 135 136 140 135.2 N16 150 160 170 143 158 156.2 N17 171 156 158 152 155 158.4 N18 149 168 136 143 152 149.6 N46 173 146 147 158 147 154.2 N46-s 181 163 171 174 199 177.6

Based on table 2 was drawn the chart of average hardness distribution on nodes of

right subassembly. For establishing the distribution mode of hardness on bottom side compared with top side are drawn the charts in figure 5 and 6.

Figure 5. Hardness distribution – top side (right subassembly)

Figure 6. Hardness distribution – bottom side (right subassembly) For establishing the distribution mode of hardness on bottom side compared with top

side for the left subassembly, is drawn table 3 and then are drawn the charts in figure 8, 9.

Figure 7. Geometric system - left subassembly

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Table 3. Hardness values - left subassemblyNode Hardness values [HB] Average

N01´ 103 100 95 103 123 104.8 N02´ 141 108 124 116 133 124.4 N03´ 89 101 111 89 97 97.4 N04´ 137 98 105 106 100 109.2 N05´ 117 130 102 119 143 122.2 N06´ 146 130 145 150 154 145 N07´ 141 142 131 120 130 132.8 N11´ 110 101 103 106 103 104.6 N12´ 97 101 82 109 99 97.6 N13´ 158 148 127 131 135 139.8 N14´ 95 97 96 103 95 97.2 N15´ 136 145 142 132 146 140.2

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.