Microscopic Examination of Play‐Worn Steel Music Strings

Friction and Wear Research, Volume 3, 2015 www.seipub.org/fwr doi: 10.14355/fwr.2015.03.001

Microscopic Examination of Play‐Worn Steel Music Strings Ferhat Bülbül*1 Department of Mechanical Engineering, Ataturk University, Erzurum, Turkey *1

ferhat.bulbul@atauni.edu.tr

Abstract The wear tests on the strings made from ASTM‐A228 music wire were performed by using bağlama, a stringed instrument.

These tests named as play‐tests were carried out by reciprocating‐sliding with finger on Do major and contrariwise scales for different durations at andante moderato speed of 100 beat per minute and by plucking with the plectrum under steady environmental conditions. The increase in the electrical resistance of the string proved that the steel string suffered a massive loss as a result of play‐wear. Wear tracks obtained via SEM showed that the level of surface damage increased and became more pronounced depending on the beat amount. The results of the present study show that tribologists and acoustists should focus on wear‐acoustic relationships of strings. Because almost all kinds of data obtained about the surface wear of music strings can also shed light on all stringed instruments.

Keywords Wear; Steel; String; SEM; Music

Introduction The origin of stringed instruments dates back many centuries ago. Most of the ancient cultures developed different stringed instruments. They have played an essential role in the history of music and in the development of contemporary music. Like guitar, violin and mandolin, bağlama is also a stringed musical instrument, similar to the Bouzouki, shared by various cultures in the Eastern Mediterranean. Up till now, in many cities of world and Europe, numerous bağlama recitals or concerts have been given, in the leadership of famous bağlama virtuosos; in these recitals Eastern music melodies have been brought together with Western music melodies, namely, especially with Spanish music, Jazz music and Classic music. Thanks to these significant works, bağlama has gained a universal dimension today.

Solid steel, rope or cable core steel, synthetic, and gut are the most commonly used string core materials for stringed musical instruments. Each type of core material has distinctly different tonal and playing characteristics.

The outer wrapping can be made from a wide variety of materials, including nylon, aluminum, chrome, steel, stainless steel, tinned steel, tungsten, nickel‐silver, silver, silver‐plate, and gold. Each material provides its own unique tonal and tactile characteristics, as well as varying degrees of resistance to wear and corrosion (primarily from contact with the playerʹs fingers). Steel strings are more economical, and they produce larger, brighter volumes of sound with a minimal break‐in period compared to others.

The strings of stringed instruments such as bağlama, guitar, violin, lute and mandolin are subject to external effects such as tension, pressure, wear, temperature, humidity, dust and light. Therefore, strings should be cleaned after performing, otherwise their timbre will get worse and the sound quality may deteriorate. Despite what we have mentioned above, the failure of strings is inevitable since the musician applies pressure with his hand and sliding causes wear on the strings, and also the sweat of hand and ambient air have a corrosive effect on the strings. In time, such activities spoil the timbre of the strings completely so that they became useless. Essentially, the strings are changed with new ones, generally depending on the play time [1].

Although a vast number of theoretical and experimental studies are available on music strings since BC, a great majority of these studies are concerned with the number, gauge, material and acoustic characteristics of strings [2‐ 13]. Pythagoras [6], the first known string theorist, during the sixth century BC, studied vibrating strings and musical sounds. He apparently discovered that dividing the length of a vibrating string into simple ratios produced consonant musical intervals. Using a vibration microscope proposed by Lissajous, Helmholtz observed

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the stick‐slip motion of a violin string during bowing, from which he deduced the sawtooth waveform of the string displacement, now commonly referred to as Helmoltz motion [2]. The 20th century made considerable gains in string construction. Kondo [14] disclosed a musical instrument string with a core wire and a helically wound covering wire where the winding pitch was greater than the diameter of the covering wire. The purpose was to eliminate contact between adjacent turns so that frictional losses at winding interfaces can be eliminated. The aging problem which is critical for steel strings was studied theoretically and experimentally by Allen [3]. Consequently, it seemed that the main cause was the increased damping due to foreign material that quickly became embedded between the windings. Pickering [4] explained that the elasticity (Young) modulus for steel was about 40 times greater than for nylon, and static string tensions were about 50% greater, so the longitudinal and transverse force amplitudes would be more nearly equal. The physical properties of some widely used violin strings were carefully measured by Pickering [4,5,15]. Keisuke [16] argued that the level of the surface hardness could be raised by such methods as phosphate coating, vapor plating, flame coating or ion plating etc., when the base material was an alloy.

In addition, he explained that the repeated vibration of the string increased the friction coefficient between the core wire and the winding wire, and the friction between these two wires lost a part of the vibration energy generated in striking or plucking the string, so that the sound volume decreased, and also the noise generated by the friction would cause a distorted or unclear musical tone, when a metal having a high ductility is used for the winding wire or the core wire [8]. Goodway [7] reviewed, from the historical point of view, the technology of music metals.

Birkett and Poletti [9] surveyed the historical process of the production and industrially usage of iron and steel as music string. By Jansson [10], the fundamental string theory was summarized, i.e., the relations between acoustical properties such as resonance frequencies and vibration sensitivity, and mechanical properties such as the mass (weight), length, and tension of the string were given. The influence of the string diameter on the string inharmonicity was demonstrated. Finally the mass increase by winding of a string without making it stiffer had been shown. Besides, the mechanical and acoustical properties had been presented for violin and guitar strings.

Further the principles for the vibrations of the strings had been sketched for differences in plucking and bowing of the string. Kitto [11] introduced a detailed description of the specific design issues involving the materials science of stringed instruments. Kitto expressed that the material properties and material science were important for musical instruments and music strings produced sounds because of their elastics constants, densities and composite structures. Schumacher et al. [12] stated that friction force during slipping showed complex behavior, not well correlated with variations in sliding speed, so that other state variables such as temperature near the interface had to play a crucial role. They suggested a new constitutive model for rosin (used as a friction material) friction, based on the repeated formation and healing of unstable shear bands. Kucukyildirim et al. [13] investigated that the abrasion and corrosion behaviors of electric guitar strings’ depended on playing periods.

They have stated that the weights of conventional and the nano polymer‐coated strings were reduced as a result of abrasion wear as playing time increased. However, the sound quality of especially conventional strings was much worse than that of the nano polymer‐coated while the corrosion resistances of nano polymer‐coated strings were better than that of conventional electric guitar strings after playing. As a result, it has been reported that better abrasion and corrosion resistance obtained stemmed from protective nano coating. An investigation of a number of service failures of the hard steel strings of plucked musical instruments was reported by Olver et al. [17]. All the failed strings were found to contain transverse fatigue cracks, mostly located near the end of the vibrating length (e.g. at the ‘‘bridge’’ of the instrument) and extending to about one third of the section thickness. An analysis of the service stresses showed that the strings are subjected to high mean tensile stresses resulting principally from elastoplastic bending opposite the failure location. It is shown that a small cyclic axial tension arises from repeated plucking during playing and this can lead to fatigue initiation and propagation over a large proportion of the wire cross section. Neither surface nor bulk defects, wear and contact stresses were found to be factors of importance in the cases examined, contrary to some speculation. Olver et al. [17] examined a number of service failures of guitar, electric bass and mandolin, steel (music wire) strings by SEM. They suggested that fatigue was the main cause of failure and the failures were associated with plastic bending at the bridge or nut of the instruments.

As seen in above‐mentioned studies, none of them addresses the fundamental problem of wear on a string.

Accordingly, the scientific literature about the effect of play‐wear and other negative factors on the sound quality of strings, and especially about their present modifications (i.e. deposition techniques), the characterization and the optimization of related parameters etc. have been unfortunately limited. Due to the commercial competition

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among string producers, general technical knowledge about them in market reflects an advertisement character or does not include much detail. For example, the group strings sold in a pocket usually do not contain any technical information apart from string gauge and material. Most string players have to change their strings in a time, for about two weeks to six months depending on playing. Although the string may still appear to be in good shape, over months of playing, strings gradually lose their brilliance and responsiveness. Finally, there is unfortunately not enough scientific information and special study in the literature about the results relating to real strings with the exception of a single study by Bülbül and Karacali [18]. Therefore, still more work needs to be done in order to obtain cheaper strings and strings with better features. One of the main aims of this study is to emphasize this issue.

Therefore, the present research focuses on the mechanical effects on uncoated steel strings due to playing.

Furthermore, the present study includes some special purposes, such as, to indicate that much more scientific work needs to be done on the modification of music strings and to prepare a ground on the relationship between playing and wear for the development of new perspectives. Namely, if this relationship is well analyzed and is more commonly used to gain more accurate information depending on the amount of beat in terms of wear‐sound feature, it will help to find the opportunity to meet the needs of today’s stringed instrumentalists as well as more technical prescriptions. That is, the fundamental information gathered about bağlama strings can also be used for other stringed instruments such violin, guitar and mandolin strings.

In this study, the play‐wear tests for 10, 30 and 60 minutes at andante moderato speed of 100beat per minute were performed by reciprocating with finger on the regions of Do (C) major and contrariwise scales of the music strings (Ø20 diameter) made from ASTM A228 steel (music wire). Low level resistance measurement was employed in order to determine the losses caused by wear. Later, some examples of SEM images of the worn regions were obtained.

Experimental Medium The tuning and the wear tests were carried out in a quiet room. The relative humidity, illumination, temperature and sound level were measured at 46%RH, 0.18lux, 25C and 20dB by using Multi‐Function Environment Meter with C.E.M‐DT8820 4 IN1 trade mark, respectively. Music strings are cold‐drawn spring steels and show certain qualities such as high tensile resistance, uniform mechanical and good thermal properties. The material of the strings of bağlama, which was used in wear tests, was high carbon steel, which meets ASTM A228 standards [19].

The diameter, chemical composition, unit mass and density of the string are 0.20mm, 0.85%C, 0.40%Mn, 98.75%Fe, 0.245g/m and 7.8x103kg/m3, respectively. Hence, Figure 1 presents SEM photo of an unworn string.

FIG. 1 TYPICAL SEM PHOTOGRAPH OF UNWORN STRING

The Properties and Tuning of the Stringed Instrument A stringed bağlama, with long neck made of juniper wood, was used as a play instrument and was picked with a thermoplastic plectrum (Fig. 2). The form (chest) length, string length (between two thresholds) and neck length of

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the bağlama were almost 43, 91 and 57 cm, respectively. The tuning was done on the basis of the bottom‐string note of the bağlama accord order (disordered/its Turkish mean is Bozuk or Kara order), which is a well‐known and widely used arrangement for bağlama. According to this, at each session before wear takes place, the strings were tuned to A3 (or third octave La) note giving 220Hz by using both a tuner with Seiko SQ 100‐88 trade mark and NI LabVIEW Signal Express Tektronix Edition program connected to the oscilloscope. In this case, the test strings had been fastened in with almost a total tensional force of 4kg on the bağlama, where the tensional force was calculated from the frequency equation depending on the force‐string length‐area.

Play‐wear Tests String wear occurs as a result of both mechanical wear and corrosion. Therefore, in order to minimize the effect of corrosion and to determine the effect of only mechanical sliding wear on the strings, the hands should be cleaned before each play process. Hands were washed with antibacterial soap and water, and then thoroughly dried with a dryer. The effect of sweat in hands was negligible in this study. This treatment was repeated before each test.

Furthermore, string stability is also strongly affected by temperature and humidity. Thereof, as mentioned above, a stable environment for play‐wear room was preserved. Consequently, all experimental conditions affecting the strings were fixed apart from mechanical wear process.

There are many different types of scales. There is the backbone of music. A major scale has 7 notes. In music theory, the major scale or Ionian scale is one of the diatonic scales. For instance, in solfege the notes of Do (C) major scale are named as Do, Re, Mi, Fa, Sol, La, Ti (or Si) or another notation that is used is C‐D‐E‐F‐G‐A‐B. Pitches are also named after the first seven letters of the alphabet (A‐B‐C‐D‐E‐F‐G). At first, the only way for the composer to indicate the speed of composition to the performer was to indicate a relative speed, but these terms are very subjective. However, metronome indication is a more precise method of conveying the speed of music. The objective, precise metronome marking is usually supplemented by subjective descriptive words (e.g. andante: leisurely walking tempo, 80‐100bpm; moderato: moderately, 100‐120bpm; allegro: fast, 120‐160bpm and presto: very fast, 160‐200bpm), usually in Italian, but sometimes in French, German or English.

FIG. 2 (A) SLIDING ABRASION WEAR BY FINGER AND (B) IMPACT EROSION WEAR BY PLECTRUM

Taking into account these additional musical knowledge, the strings were worn out by reciprocating with finger on totally 14 pitches at once forth Do major scale and once back contrariwise scale (Si, La, Sol, Fa, Mi, Re, Do), as shown in Fig. 3. That is, the actual frequencies of each fretted note are 130.81Hz for Do (C3), 146.83Hz for Re (D3), 164.81Hz for Mi (E3), 174.61Hz for Fa (F3), 196Hz for Sol (G3), 220Hz for La (A3) and 246,94Hz for Si (B3).

Table 1 shows the contact conditions for play‐wear in summary. The hitting on chest and the sliding (reciprocating) movement on the neck (fingerboard) of string occurs during the play‐wear of a bağlama as shown in Fig. 2 (See Section See Section “Wear Mechanisms” in “Results and Discussion”). The reciprocating wear process of one cycle on the strings was applied for 10, 30 and 60 minutes at andante moderato speed of 100 beat per minute. Here, the tempo was set by the tuner. On the other hand, the chest regions were also stroked with the plectrum while the first finger touched on the strings by reciprocating. At the end of each performed cycle, the low level resistance values of strings were determined without detaching the strings. After detaching, their sections were excised from the worn regions corresponding to Do (C note), Fa (F note) and Si (H note) and, then photographed by SEM.

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FIG. 3 THE PLAY‐WORN REGIONS AND BEAT STYLE WITH THE PLECTRUM TABLE 1 CONTACT CONDITIONS FOR PLAY‐WEAR

String

‐Specification: ASTM A228 music wire ‐Diameter: 0.20mm ‐Unit mass: 0.245g/m ‐Density: 7.8x103kg/m ‐Hardness: 45 Rockwell‐C

Stringed instrument

Long necked bağlama made from juniper Its fingerboard made from beech (Hardness, Wood indentation: 4600N)

Abrasive counterparts

‐Left forefinger (for reciprocating on neck or stem region) ‐Plectrum (for stroke on chest region): Made from a thermoplastic nylon material (65 Rockwell‐R)

Medium

‐Relative humidity: %46RH ‐Illumination: 0.18lux ‐Temperature: 25C ‐Sound level: 20dB

Playing parameters

‐Initial frequency: A3 (3rd octave La) note providing a sound with 220Hz frequency ‐Tension of string: ~4kg ‐Wear region on the string: Do major and contrariwise scales (including total 14 notes) by left forefinger ‐Beat number: 6000 ‐Wear speed: 100bpm andante moderato ‐Stroke on the chest: once down (↓) and once up (↑) with the plectrum

Resistance Measurement The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross‐sectional area, and proportional to the resistivity of the material. The resistance R of a conductor of uniform cross section can be computed as R= ℓ. ρ /A (where ℓ is the length of the conductor, measured in meters; A is the cross‐sectional area, measured in square meters; ρ is the electrical resistivity (also called specific electrical resistance) of the material, measured in Ohm‐meter.)

Resistivity is a measure of the materialʹs ability to oppose electric current. DC voltage, DC current, and resistance are usually measured with digital multimeters (DMMs). Generally, these instruments are adequate for measurements at signal levels greater than 1μV or 1μA, or less than 1GΩ. However, they do not approach the theoretical limits of sensitivity. For low level signals, more sensitive instruments such as electrometers, picoammeters, and nanovoltmeters must be used. However, instead of these systems, which are very expensive, the two‐wire methods for electrical resistance measurements can be used today. The current is forced through the test leads and the resistance (R) being measured. The meter, then, measures the voltage across the resistance through the same set of test leads and computes the resistance value accordingly [20]. That is, voltage is read by

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keeping firm the current and electrical resistance is calculated from R=V/I equation.

To determine whether any mass loss is caused by wear, even if it is very small scale, the following low level resistance measurement circuit was built deriving from R=ℓρ/A equation used for measuring low level resistance.

Accordingly, the resistance must theoretically increase as the cross‐sectional area is reduced. In the present study, the loss occurred by wear damage is experimentally at nanometer level and so the resistance increased. This cross‐ sectional change can be measured by low level resistance measurement.

The circuit is composed of a DC power supply with GW‐Instek GPS‐3303 trade Mark and two digital multimeters with Brymen BM837RS trade mark. According to this, while one of the multimeters served as a voltmeter, the other functioned as a current meter, and bağlama string was also used as a resistor. The resistance after each play‐wear session was measured, provided that two poles of the electrical resistance were between lower‐threshold and upper‐threshold. Fig. 4 shows the constructed circuit schema.

FIG. 4 THE SCHEMATICALLY DISPLAY OF CIRCUIT CONNECTION ASSEMBLED FOR LOW LEVEL RESISTANCE MEASUREMENT

SEM Studies Before microscopic evaluation and dismantling, plastic molds with a radius of approximately 0.1mm channels were placed under the locations of the strings that correspond to Do, Fa and Si frets, embedding such locations inside those channels (Fig. 5). After that, the molds were fixed with a strong glue and they were left to dry. After they dried, the strings were cut through and their photographs were taken using SEM. These actions were repeated for each abrasion process.

FIG. 5 STRINGS EMBEDDED INTO MOULDS

Results and Discussion Examination of Wear Tracks by SEM SEM photos (Figs. 6 to 11) were obtained from the string parts chosen by making sampling both from Do, Fa, Si pitches abraded by finger and from the chest regions stroked with the plectrum.

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FIG. 6 SEM IMAGES TAKEN FROM (A) DO, (B) FA AND (C) SI PITCH‐STRINGS WORN FOR 1000 BEATS

Neck‐strings

FIG. 7 SEM IMAGES TAKEN FROM (A) DO, (B) FA AND (C) SI PITCH‐STRINGS WORN FOR 3000 BEATS

When the images obtained from neck‐strings in Figs. 6 to 9 are examined, it is understood that the straight tracks in different directions were generated as a result of the micro‐cutting of the string by finger skin (horny cell layer) and the abrasion by wear particles separated perhaps from finger skin and/or steel string surface. Sugishita et al. [21] touched on the same reasons for tactile wear on a metal. While ploughing (low‐stress) or plowing, in one of the

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abrasive wear modes [22], indications are observed in the mode of straight lines on the string taken from Do pitch (C note) (in Fig. 6a), the quantity and the depth of the track increase, and debris sprout as abrasion products on that of Si pitch (H note)‐string (in Fig. 6c) attract attention. As shown in Fig. 7a, it seems that as if the wear tracks are closed and partly flattened due to the reciprocating action that has happened in the previous session. Namely, for Fa note, a clear wear region is formed as a result of repetitive reciprocating (Fig. 7b). However, it appears that the depth of the wear tracks has become bigger for especially Si (H note)‐string (Fig. 7c).

Figs. 8 and 9 show the tracks belonging to Do, Fa, and Si pitch‐strings worn for 60 minute (frayed string of 6000 beats), respectively. The pits and abrasive particles having the diameter of some 10‐20μm on Do pitch‐string rose. It draws attention that the wear debris for Fa pitch‐string are dragged along or carried towards the sides of the string depending on the increasing beat amount (Fig. 8). Namely, the wear track view of the string frayed on Fa pitch was more stable according to that of others. However, the wear damage was note‐worthy for Si pitch‐string frayed for 6000 beats (Fig. 9). From this, it can be said that the wear on Do and Si ‐ the starting and finale pitches (points) of the Do major scale and contrariwise scale, respectively, and as if they are knot points ‐ is more drastic than that of Fa‐string, but Si pitch‐string has the most damaged regions. As a consequence, the amount, depth, dimension of wear tracks and abrasive debris increased gradually with the increasing beat amount.

FIG.8. SEM IMAGES TAKEN FROM (A) DO AND (B) FA PITCHES ON THE STRING WORN FOR 6000 BEATS

From SEM views, it is evaluated that a variety of wear actions‐ from ploughing abrasion to chip formation and dragging, clustering and separations in the form of flakes‐ rise due to the beat amount. It is believed that stick‐slip has an important effect on the formation and transformation of these wear‐phenomena on the surfaces of string.

Namely, the stick mechanism is more dominant than the slip on Do and Si note‐strings while the slip mechanism on Fa pitch‐string is more effective. It is considered that the wear tracks taken from Fa pitch‐string are more stable and smoother due to the factors mentioned above. Furthermore, the wear damage of Si pitch‐string is the most drastic of all, which produces the most abundant and the biggest wear debris. The possible causes of this would be that since Si pitch is only a knot point and greater damages at the “Si” position almost certainly arise because of greater sliding between the string and fret at this position, which is nearer the centre part of the open string length, among others, Si is a note sounding at the highest frequency in addition to the dominant stick mechanism together with slip developing. In addition, the frequency will also increase as the vibration number increases along string as the string reduces locally its diameter, thus, the mass, due to the beats depending on playing time, which is confirmed by Mersenne’s equation (see next section for the details of the equation). Consequently, more acoustic

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energy dissipation and tonal losses occur. Because, an increase in the vibration based on increasing frequency results in the disclosure of more phonons (as matter) and more acoustic energy, taking into account relativity and superstring theories.

FIG.9. SEM IMAGES TAKEN FROM SI PITCH ON THE STRING WORN FOR 6000 BEATS

Chest‐strings The micrographs taken from the chest region‐strings by SEM are shown in Fig. 10 for 1000, 3000 beats, and in Fig. 11 for 6000 beats. Hence in such regions, the level of wear damage increases as the beat amount increases. In Fig. 10a, it is seen that the wear products take the shape of a drop or a flake and are partly clustered towards the edges.

From Fig. 10b, it can be said that the heterogenic tracks are developed in diverse directions and they are more prominent, and the amount of the clustered wear debris increases.

FIG.10. SEM IMAGES TAKEN FROM CHEST REGIONS OF THE STRING WORN FOR (A) 1000 AND (B) 3000 BEATS

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Fig. 11 shows that the clustered wear debris is broken off in the form of layers with the plectrum strokes together with the beat amount.

The basic wear mechanism, which occurs with the strokes of plectrum on the string, are erosion caused by hitting, which happens as a result of repetitive impacts on opposite direction. Thus, small chips were broken off from the string surface as a result of the vibration caused by the striking of polymer plectrum repeatedly on the same region of chest. Therefore, the wear on the chest‐string was more intense than that of neck region where stick‐slip was the featured mechanism. As a result, it can be said that the chest‐strings had more wear product than that of neck‐ strings.

FIG.11. SEM IMAGES TAKEN FROM CHEST REGION OF THE STRING WORN FOR 6000 BEATS

Resistance of Play‐worn Strings The results of low level resistance measurement before and after the wearing of strings are given in Table 2, and Fig. 12 also shows the relationship between the beat amount and electrical resistance. It is seen that the resistance value increases with the beat amount. While deviation in roughness is less than 0.5%Ra (average surface roughness), the difference between RM (the resistance obtained from multimeter) and Raverage (average resistance) is 5 digits, which means that 5 zeros from the right of the comma are significant.

TABLE 2. LOW RESISTANCE VALUES OBTAINED DEPENDING TO THE BEAT AMOUNT

Beat number

0

1000

3000

6000

Electrical Resistance Ω

7.18533

7.19458

7.20039

7.20647

It has attributed to the resistance to be inversely proportional with the cross‐sectional area decreasing with the increasing beat amount. The reduction in cross‐sectional area was not homogeneous for the whole string with regard to the nature of the abrasion mechanism. Thus, variable section areas led to the non‐uniformity of the section. If these section areas are represented as having different resistance values, then they will gather, get stronger and increase the total resistance, considering that they form a serially connected system. Mersenne [23], referred as the father of acoustics, has explained that the fundamental frequency of a vibrating string is proportional to the square root of the tension and inversely proportional both to the length and the square root of the mass per unit length. In the equation of ƒ=1/2ℓ (F/m)1/2, ƒ is frequency (Hz), ℓ is vibrating length between two

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thresholds (m), F is tension force (N) and m is the specific mass of string (kg/m). The frequency will also increase as the vibration number increased along string as the string reduces locally its diameter, thus, the mass, due to the beats depending on playing time. Consequently, the acoustic energy more dissipates and tonal loss occurs. Because, an increase in vibration depending on the increasing frequency means that more phonons (as matter) and more acoustic energy are emitted, taking into account relativity and superstring theories.

FIG.12. BEAT AMOUNT‐RESISTANCE RELATION

Wear Mechanisms It is a fact that everything wears out in time. For instance, the stairs are worn by steps, the glasses are rubbed out by cloth, the car bonnet is washed by pressured‐water, the stones are eroded in flowing streams, keys (of a piano, typewriter, etc.) are worn by fingers, etc. Repetition is more important for the wear modes such as pitting, fretting, spalling, impact, brinelling, solid particle impingement, liquid impingement, cavitation, and slurry erosion and partly polishing. Although thermoplastic plectrum is softer than steel, the damage on string is inevitable due to reciprocating sliding movements and repetitive impacts. Fig. 13 illustrates the characteristics of the scratches formed on a string surface as a result of sliding abrasion by finger and impact erosion by plectrum, and the factors of play‐wear are given in Table 3. There is a very simple explanation for why soft materials wear away easier than the harder ones. The world is a dusty place and all surfaces will have some dust particles on them. If the softer material is moving faster than the harder material, the harder material will be removed. This is why you can polish diamonds. Some polishing wheels are made of cloth. One of the abrasion wear types is also polishing wear.

Polishing wear is the progressive removal of material from a surface by the action of rubbing from other solids in such a way that material is removed without visible scratching, fracture, or plastic deformation of the surface. It is put in the category of abrasive wear because polishing produces microchip removal. Rabinowicz [24] proposed a mechanism of molecular removal. Atoms or molecules are individually removed from the surfaces by the rubbing counterforce. It is obvious that polishing can occur by repeated rubbing of almost anything. Steel handrails on well‐used stairs often are polished from the rubbing of people’s hands. The likely mechanism in such cases may be something akin to Rabinowicz’s proposal. In any case, polishing wear is a significant wear process with uncertain mechanism: but in cases where hard substances are part of the wear system, material rules of low‐stress abrasion (ploughing) apply [21]. Here, the abrasion wear process applied by finger on the neck‐string is also a polishing wear, because the finger appears to play a role as a fine scale abrasive. Furthermore, the mechanism of wear applied by the plectrum on the chest string is the impact erosion, which is one of the types of erosive wear.

Accordingly, scratches appear due to both abrasion sliding wear by repetitive reciprocating movement of finger and erosive wear by repetitive impacts of plectrum on the strings.

If spiny lobsters’ stick and slip mechanism, suggested by Patek [25], and Patek and Baio [26], is compared to bağlama stringed instrument, it can be said that the finger functions as a plectrum while the stick‐slipped string acts as a file, because the tactile wear with the finger will occur on the string.

One of the mechanisms debated about the nature of the polishing abrasion process is the melting of surface layers.

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The high temperatures generated because friction soften the asperities of the surface of the work‐piece, resulting in a smeared surface layer. However, it cannot be said for play‐wear system on the string because melting and softening on string do not occur due to low compression loads that the finger applies onto string at low sliding speeds and also hitting of the plectrum on string by small forces.

FIG.13. CHARACTERISTIC OF SCRATCHES FORMED ON A STRING SURFACE AS A RESULT OF (A) SLIDING ABRASION BY FINGER AND (B) IMPACT EROSION BY PLECTRUM TABLE 3. FACTORS OF PLAY‐WEAR

Play‐wear

External effect

Mechanical

Environmental*

Wear instigator

Finger

Plectrum

Tear, dirt, sand

Direction of movement

Reciprocating (↔)

Repetitive stroke (↨)

‐

Wear region

Neck (stem)

Chest

Over all

Basic wear mechanism

Abrasion

Erosion

Corrosion

Specific category

Low‐stress abrasion (sliding or ploughing)

Impact

Oxidation

Special definition

Stick‐slip

Hitting/Stroking

Tribo‐corrosion

* Environmental effects were ignored in the present study

Conclusions 

“Play‐wear” as a specific term, which, so far, has not been reported by tribologists or acoustists, is used in literature in this study along with previous study for the first time [18].

 The abrasion wear process applied by finger on the neck‐string can be defined as a polishing wear. Because the finger rubs repeatedly as a reciprocating fine scale abrasive. Thereby, this movement means sliding or ploughing wear. Furthermore, hitting by the plectrum is applied on the chest string. This wear mechanism is the impact erosion which is one of the types of erosive wear. Accordingly, the scratches appear due to

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both abrasion sliding wear by repetitive reciprocating movement of finger and erosive wear by repetitive impacts of plectrum on the strings. 

Wear tracks obtained by SEM showed that the level of surface damage increased and become more pronounced depending on beat amount. Accordingly, the playing damage was note‐worthy even if the wear or the beat amount was not very high.



The string reduces locally its diameter, which increases the electrical resistance, as music steel string suffers wear due to the beats.



The stick‐slip mechanism for stringed instruments, described by Patek, is analogous to bağlama.

Accordingly, the finger, the abrasive counterpart, corresponds to a plectrum, while the string served as a file.



We can realize the significance of the dominant stick effect of the stick‐slip mechanism at the starting and the finishing points of the stick phenomena. Still, for a plucked stringed instrument the slip effect exists at every point of the reciprocated‐string. It is interesting that the wear damage in Si pitch (H note)‐string is more intense than that of Do (C note)‐string. A reason for that could be the Si (H note)‐string having the highest frequency. Because, an increase in vibration due to increasing frequency results in the disclosure of more phonons (as matter) and more acoustic energy, taking into account relativity and superstring theories, thus causes more tonal loss.

ACKNOWLEDGMENT

This research is a part of a TUBITAK (The Scientific and Technical Research Council of Turkey) project supported by grant no: 107M647. The author would like to thank TUBITAK for funding the project. Besides, author thanks Atatürk University (grant no: 2007/151) for providing partly financial supports and Assoc. Prof. Dr. Tevhit Karacalı for his help.

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Ferhat Bülbül is an associated professor of Material Science at the Department of Mechanical Engineering of Ataturk University. The current research interests include: Solid lubricant coatings, hard coatings, sputtering deposition, electroless deposition, tribology (friction‐wear‐lubrication), and wear at stringed instruments.

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