JAYASWAL PRATESH AND CHAKRABORTY ABHISHEKDepartment of Mechanical Engineering, Madhav Institute of Technology & Science, Gwalior-474005, India

ABSTRACT

Spring is a mechanical device which is primarily used toabsorb shocks. It is also employed to provide a flexiblelink in certain mechanisms, like in the brake pedalmechanism of a two wheeler. The authors have selectedthe coil spring of a two wheeler, connected with the brakepedal for the study, as it operates under severe workingconditions. The material used to manufacture coil springis called spring steel (IS: 4454) which primarily consistsof iron. The iron percentage of a spring gets deterioratedby considerable amount during its prolonged use. Therate of deterioration depends upon the area of applicationof the spring and service conditions. Spectrophotometricanalysis technique has been used to determine thepercentage composition of iron in various spring samples.The experimental results show that the iron compositiongets decreased gradually, as the spring age increases.

Keywords: Brake pedal, Coil spring, Spring steel,Spectrophotometer

1. INTRODUCTION

Failure analysis of a mechanical component is doneas part of its condition monitoring to predict failure.The results of failure analysis provide necessaryinformation regarding the root causes of failure;precautions need to be taken to prevent failure; theaverage life of a component; effect on performancewith ageing; physical and/or mechanical changesin the component etc. Failure analysis of a coilspring can be done by testing the strength ofsamples using spring testing machine or by usingchemical analysis techniques. The samples underconsideration are the brake pedal springs of BajajDiscover motor bikes. These coil springs are madeup of spring steel of grade IS: 4454. The metalliciron of a spring gets oxidized due to its exposure toatmosphere, which eventually results in its rusting.This material deterioration results in decrease in thestrength of spring in terms of its toughness andresilience properties, and thus, leds to spring failure.This is so because as the percentage of metallic irondecreases, the above mentioned properties also getreduced. The authors have followed absorptionspectroscopy technique to determine the

composition of iron in the samples of different age.The objective of this research work is to demonstrateat what rate the percentage of iron in a springdecreases during age. The results would help todetermine the average life of a brake pedal springand thus it’s time of replacement, before it fails.

2. PREVIOUS RESEARCH

Many techniques have been followed byresearchers to conduct failure analysis of differenttypes of coil springs, employed in variousmechanisms. R. Rivera et al. [1] studied the causesof the premature rupture of a spring from anelevator door control mechanism using SEM. S. S.M. Tavares et al. [2] investigated the failure of twoPSV springs working in same conditions in off-shore oil platforms by following chemical analysisusing plasma spectroscopy, examination of thefractures with stereo-microscope, microstructuralanalysis of the material of the springs and byhardness measurements in samples collected nearthe cracks location. Himadri Roy et al. [3] examinedthe premature failure of a coil spring used in a fuelpump bracket assembly using SEM. Y. Prawoto etal. [4] discussed several case studies of suspensionspring failures using FEA of stress distributionsaround typical failure initiation site. The failurespresented range from the very basic includinginsufficient load carrying capacity, raw materialdefects such as excessive inclusion levels, andmanufacturing defects such as delayed quenchcracking, to failures due to complex stress usageand chemically induced failure. S.K. Das et al. [5]carried out investigation on the premature failureof suspension coil spring of a passenger car, whichfailed within few months after being put intoservice. The experimental techniques used for theinvestigation were microstructural analysis andfractography by scanning electron microscopy(SEM), inclusion rating by optical microscopy,hardness testing, residual stress measurement by

44 Jayaswal Pratesh and Chakraborty Abhishek

X-Ray diffraction (XRD) and instrumental chemicalanalysis. Matt Landrigan [6] recovered fracturedsurfaces and made observations under SEM andElectrical Dispersive Spectrometry (EDS). Vickersmicrohardness test was also performed to confirmthat the spring was well within operatingconditions. L. Del Llano-Vizcaya et al. [7] appliedmultiaxial fatigue criteria to the analysis of helicalcompression springs using the critical planeapproaches, Fatemi–Socie and Wang–Brown, andthe Coffin–Manson method based on sheardeformation. B. Ravi Kumar et al. [8] analysed thefailure of a helical compression spring employedin coke oven batteries using chemical analysis,surface corrosion product analysis, Fracture surfaceanalysis, Metallography and hardness and residualstress analysis. K. V. Sudhakar [9] conducted failureanalysis of an automobile valve spring. Thefractured surfaces as well as the surface of the springmaterial close to the fractured surface wereexamined in a scanning electron microscope atsuitable magnifications. Optical microscopy wasalso performed to evaluate the basic microstructureof the as-received material. B. Ravi Kumar et al [10]analysed the premature fatigue failure of acompression spring during service by employingoptical and scanning electron microscopy, hardnessand tensile testing and X-ray diffraction techniques.

3. DATA COLLECTION & EXPERIMENTATION

For this present experimental work, all the springsamples are collected from the different variants ofBajaj Discover motor cycle. The sample details arelisted in Table 1.

Table 1Sample Details

Sample Sample PhotographNo. Details

I New (Unused)

II Model: Discover(100cc)Age: 11,782kmReg. No: MP07/MJ/ 0634

III Model: Discover(100cc)Age: 11,967kmReg. No: MP07/MJ/ 8255

IV Model: Discover(100cc)Age: 13,345kmReg. No: MP07/MJ/ 2693

V Model: Discover(125cc)Age: 18,957kmReg. No: MP07/KK/ 9950

VI Model: Discover(135cc)Age: 20,991kmReg. No: MP07/MJ/ 8255

VII Model: Discover(112cc)Age: 48,000kmReg. No: MP07/MB/ 2177

VIII Model: Discover(112cc)Age: 58,996kmReg. No: MP32/MA/ 1989

IX Model: Discover(125cc)Age: 79,929kmReg. No: MP07/KL/ 3002

3.1.Sample Processing

All the sample springs were first converted intoequivalent wires using a plier and a hammer. There

“Failure Analysis of Brake Pedal Coil Spring of a two Wheeler using Absorption Spectroscopy... 45

after equal portions of each spring wire was cutdown and grinded into powder form. In thismanner, as shown in figure 1, nine powderedsamples of 1g weight were prepared forspectroscopic analysis.

Since, all substances do not obey the linear Beer-Lambert law over all concentration ranges,therefore, a calibration curve has been constructedagainst the standard solutions, to provide therelationship between concentration and absorbanceunder the conditions used for the analysis. Threestandard iron solutions have been prepared withconcentrations of 211.00 mg/L, 296.00 mg/L and423.00 mg/L for calibration purpose, using pureiron (Fe +2) and distilled water.

Figure 1 (a): Wire form ofSample

(b) Powder Form of Sample

3.2. Spectroscopic Analysis

The purpose of this calorimetric analysis is todetermine the iron content of an unknown sample.Iron +II is reacted with o-phenanthroline to form acolored complex ion. The intensity of the coloredspecies is measured using a Shimadzu-UV Probespectrophotometer. A calibration curve (absorbanceversus concentration) is constructed for iron +II andthe concentration of the unknown iron sample isdetermined.

This analysis is based on the principle of changein the intensity of the color of a solution withvariations in concentration. Colorimetric methodsrepresent the simplest form of absorption analysis.An increase in sensitivity and accuracy results whena spectrophotometer is used to measure the colorintensity. Basically, it measures the fraction of anincident beam of light which is transmitted by asample at a particular wavelength. For any givencompound, the amount of light absorbed (A)depends upon the solution concentration (c) (moleslitre-1), the path length (L), and the wavelength (ë).Absorbance is related to the concentrationaccording to the Beer-Lambert law:

A = �cL

where � is the extinction coefficient (M-1cm-1). Inthis experiment, ��= 500 nm L = 1 cm. First all thepowdered samples, each of 1 g weight, weredissolved in equal volumes of aqua-regia to form aliquid medium for chemical analysis. Then, all theFe3+ ions are reduced to Fe2+, in order to bequantitative, by the use of an excess ofhydroxylamine hydrochloride as follows-

4 Fe3+ + 2 NH2OH•HCl � 4 Fe2+ + N2O + 4H+ + H2O

Ferric Iron Hydroxylamine Hydrochloride Ferrous Iron Nitrous Oxide Proton Water

Figure 2 (a) SampleWeighing

(b) Sample SolutionPreparation

(c) Spectrophotometer

The calibration curve generated by thespectrophotometer is shown in figure 3, whichindicates the corresponding absorbance of eachsolution.

Figure 3: Calibration Curve

Thereafter, analysis for iron was done byreacting iron +II with o-phenanthroline to formsample solutions of an orange-red complex ion.

46 Jayaswal Pratesh and Chakraborty Abhishek

Finally, all the sample solutions have been putin separate quartz cuvettes and placed inside thespectrophotometer, one by one, to get the respectiveiron compositions. The spectrophotometerperforms as per Beer-Lambert law.

4. RESULT & DISCUSSION

The outcome of UV visible absorption spectroscopytechnique on the nine samples are shown in table2, which shows the percentage composition of Fe+2 in all the samples.

Table 2Composition of Fe +II

Sample Age of Sample Composition ofNo. Springs (km) Solution Fe+2 (%)

Concentration(mg/l)

I New 400 100

II 11,782 391.163 97.791

III 11,967 391.024 97.756

IV 13,345 389.991 97.498

V 18,957 386.278 96.569

VI 20,991 384.256 96.064

VII 48,000 366.236 91.559

VIII 58,996 355.753 88.938

IX 79,929 340.053 85.013

From the above results, it can be concluded thatas the age of a spring increases, its percentage ofiron content decreases. This would make the springunsuitable for further use due to lesser strength. Itis further suggested that the brake pedal coil springof a two wheeler should be replaced before attainingthe age of 48,000 km. Beyond this, the iron contentwould get reduced by more than 10%, and thus,would make the spring unfit for further use.

5. CONCLUSION

In this present work, spectrophotometric analyseswere done to identify the spring condition duringlife span. The results show that the technique used

in this work is suitable and capable to identify thepresent condition of spring by measuring thepercentage composition of iron in it. It is furtherconcluded that a spring should be discarded onceits iron composition is reduced by more than 10%because after that, the strength of the spring getsreduced beyond tolerance limit.

AcknowledgmentThe authors express their deepest gratitude to MadhavInstitute of Technology & Science, Gwalior for providing fullfledged support to accomplish this research work.

References[1] R. Rivera, A. Chiminelli, C. Gómez, J. L. Núñez, Fatigue

Failure Analysis of a Spring for Elevator Doors, EngineeringFailure Analysis, 17, 731–738, 2010.

[2] S. S. M. Tavares, J. M. Pardal, L. Menezes, C. A. B.Menezes, C. D’Ávila , Failure analysis of PSV springs of 17-4PH Stainless Steel, Engineering Failure Analysis, 16,1757–1764, 2009.

[3] Himadri Roy, Debashis Ghosh, Tapas Sahoo & AwadeshShukla, Failure Analysis of a Spring for a Fuel PumpBracket Assembly, Indian Journal of Engineering & MaterialsSciences, 16, 33-36, 2009.

[4] Y. Prawoto, M. Ikeda, S. K. Manville, A. Nishikawa,Design and Failure Modes of Automotive SuspensionSprings, Engineering Failure Analysis, 15, 1155–1174, 2008.

[5] S. K. Das, N. K. Mukhopadhyay, B. Ravi Kumar, D. K.Bhattacharya, Failure Analysis of a Passenger Car CoilSpring, Engineering Failure Analysis, 14, 158–163, 2007.

[6] Matt Landrigan, Failure Analysis of a Garage Door Spring,AME 60646: Failure of Materials, 2006.

[7] L. Del Llano-Vizcaya, C. Rubio-Gonza´lez, G.Mesmacque, T. Cervantes-erna´ndez, Multiaxial Fatigueand Failure Analysis of Helical Compression Springs,Engineering Failure Analysis, 13, 1303–1313, 2006.

[8] B. Ravi Kumar, Swapan K. Das, D. K. Bhattacharya,Fatigue Failure of Helical Compression Spring in Cokeoven Batteries, Engineering Failure Analysis, 10, 291–296,2003.

[9] K. V. Sudhakar, Failure Analysis of an Automobile ValveSpring, Engineering Failure Analysis, 8, 513-520, 2001.

[10] B. Ravi Kumar, D. K. Bhattacharya, Swapan K. Das,Sandip Ghosh Chowdhury, Premature Fatigue Failureof a Spring Due to Quench Cracks, Engineering FailureAnalysis, 7, 377-384, 2000.