- Email: [email protected]
Wear of polymer horseshoes: a field investigation
Wear 255 (2003) 1300–1305
Case study
Wear of polymer horseshoes: a field investigation S. Mischler a,∗ , M. Hofmann b a
Chemin des Bosquets 2c, CH-1315 La Sarraz, Switzerland b MatSearch, 1009 Pully, Switzerland
Abstract A methodology to monitor wear behaviour of polymer horseshoes was developed and applied in a field investigation. Results show that wear is proportional to the distance run on hard grounds while other typical horse activities performed on softer grounds do not contribute significantly to degradation. Slight modifications of the shoe structure affect the distribution of wear on the shoe sole and may thus increase the lifetime. The method allowed one to quantitatively describe differences in wear behaviour among individual horses. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Wear; Horseshoe; Polymer; Field test
1. Introduction Horseshoes can affect both the foot and the entire limb [1]. The solicitation of horseshoes has changed during the time from tracks across the field to roads covered with more abrasive gravel or asphalt. The steel shoe fills an important function as it protects the hoof against wear or damage during locomotion, but it limits the shock absorbing properties and the flexibility of the hoof. It interferes with the hoof mechanism, i.e. the complex sequence of hoof deformations occurring during gait to adsorb the shock and to enhance blood circulation, hence nutrition and quality of the hoof, and therefore can increase the risk of injuries. In recent years there was a considerable development in the field of horseshoes using light materials, such as aluminium matrix composites or polymer, as alternative to the traditional steel. It was previously observed that the use of aluminium matrix composites was not a valid alternative for riding horses because of massive wearing and breakage [2]. Polymer materials having higher elasticity offer higher damping properties and an enhanced capacity of the shoes to fit the natural deformation of the hoof occurring during gait. These advantages result in a better compatibility with the hoof mechanism and a smaller solicitation of the articulations finally contributing to the wellbeing of the horse. The main shortcoming encountered when using polymers as horseshoes material lies in the intrinsic limited resistance to wear compared to steel. Normally, horses are shod every 6–10 weeks and during this shoeing period the horseshoe ∗ Corresponding author. Tel.: +41-21-866-6711; fax: +41-21-866-6711. E-mail address: [email protected] (S. Mischler).
must withstand the severe mechanical and abrasive solicitation induced by the horse activity. In many cases, even steel shoes cannot hold the required lifetime because of severe wear of the shoe. Therefore, there is a strong need to better control wear of polymer horseshoes and to develop criteria allowing one to predict their useful lifetime as a function of field conditions. The present work was initiated to develop a method to quantify wear of polymeric horseshoes and to identify critical field conditions as well as others design factors influencing wear. For this, commercial polymer horseshoes were evaluated in a dedicated field test involving nine horses active in riding schools for a total of 26 shoeing periods. The activity of the horses was monitored and wear of the horseshoe sole was measured at regular intervals during each shoeing period as well as after removal. Optical and electronic microscopy was used to identify relevant wear mechanisms. The influence of slight modifications of the shoe structure on the wear behaviour was also evaluated. 2. Experimental The polymer horseshoes used in the presented study were produced by the company HippoDynamix and are shown in Fig. 1. They consist in a two part transparent base shaped in form of a traditional horseshoe, with a bridge connecting the two ends. The base contains the nail slots to fix the shoe on the hoof with steel nails. In selected locations, wear resistant sections were inserted by co-injection that can support additional inserts and spikes for winter time riding. The base is made out of commercial polyurethane of 72 Shore
0043-1648/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0043-1648(03)00166-2
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
D hardness and the wear resistant inserts are made out of softer elastomer like polyurethane of 91 Shore A hardness (all data according to manufacturers). The polyurethane base is rigid so that it can be easily nailed and filed to fit the shoe to the hoof. The thickness of the base was 12 mm for the horseshoe sizes 130 and 140 while, for size 150, the thickness was 14 mm. Two standard horseshoe models, M0 and S0, were used: they differed in the profile height of the wear resistant inserts, either 2 mm (M0) or 5 mm (S0). The total surface of the wear resistant inserts increased with increasing horseshoe size and corresponded to approximately 40 cm2 for size 140. On some shoes, the standard wear resistant inserts situated backwards near to the heel region of the shoe were machined to provide a structured profile intended to improve flexibility and adhesion on soft grounds. Two types of structure were considered: structure S1 consisted in a number of parallel grooves (3 mm in width and depth) machined perpendicular to the shoes’ symmetry axis at a intervals of 3 mm while cubic protuberances (3 mm dimension) characterised structure S2 as shown in Fig. 1. Wear was quantified by measuring the dimensional change of the base and of the wear resistant inserts. The thickness changes of the base as well as the wear resistant inserts with respect to the base were measured in eight positions distributed on the horseshoes (Fig. 2). The difference with respect to the thickness values of a new horseshoe corresponds to wear. For each location, the wear of the base was added to the change in profile height of the wear resistant inserts to compensate for wear of the base. Shoe thickness was measured before and after removal from the horse and, for control purposes, at regular intervals during utilisation. In the latter case, only profile changes were considered. All
1301
Fig. 2. Location of measured points (crosses) on the horseshoe sole for the determination of wear in wear resistant inserts.
dimensional measurements were carried out using an electronic caliper (Tesa Digit Cal) characterised by a repeatability of 0.01 mm. However, because of uncertainties in the exact positioning of the instrument on the horseshoes, measurement repeatability was ±0.1 or ±0.2 mm for measurement after removal and during utilisation, respectively. All the horses were shoed by the same farrier after preparing the hoof to correctly fit the horse anatomy. Feet were numbered with the numbers 1, 2, 3 and 4 for the forefoot left, forefoot right, hind left and hind right, respectively. The typical weekly activity of the horses consisted in: 6 h of carrousel (ground: wood chips mixed with sand), 1 h of horsemanship (ground: sawdust) and 2 h training (ground: wood chips). In addition, depending on weather conditions, horse weekly activity included 3–6 promenades. Typically, a promenade lasted 1 h during which the horse may walk, trot, canter, and gallop for 4–5 km on hard ground (asphalt or concrete) and an equivalent distance on mixed ground earth/stones. Variations in the weekly activity were monitored and the total distance travelled recorded. At regular intervals of 1 or 2 weeks each horseshoe was observed, photographed and measured. No steel controls were used.
3. Results
Fig. 1. Polymer horseshoe mounted on left hind foot. The rear part (top of the picture) exhibits a S2 type structure. (1) Transparent base, (2) bridge, (3) nail slots and (4) wear resistant inserts.
Although nine horses were objects of the investigation for 26 shoeing periods, only results for two horses, Polka (female, Swiss half breed, 500 kg) and Quomètte (female, French half breed, 500 kg) will be presented here because they were shod the most with the polymer products under study. The consequence of wear is illustrated in Fig. 3, where a new shoe is compared to a horseshoe used for 52 days on Polka. Although the shoe is still functional after 52 days, large wear is observed in particular in the front part (toe).
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Fig. 3. Horseshoes of size 130 with 2 mm thick wear resistant sections (M0). (a) Unused and (b) after 52 days of use.
In the case of Polka, large wear was observed even with traditional steel shoes. The average wear, i.e. the average value of reduction in profile measured on the eight positions shown in Fig. 2 is plotted in Figs. 4 and 5 against the total distance travelled during promenades. Despite large scatter in the data, some proportionality between wear and distance can be observed in Fig. 5 regardless of the shoe type. In the case of Quomètte (Fig. 5) the reduced number of experimental points does not provide sufficient evidence of proportionality between wear and distance run. The normalised wear was calculated by dividing the wear measured at each location by the highest value observed, and this for each shoe. By plotting the normalised wear as a function of the measurement location, one obtains the wear distribution profiles shown in Fig. 6 for selected shoes. Fig. 6 shows the wear distribution measured on Polka, left hind foot (foot 3), for four shoeing periods with the same horseshoe type (M0). Wear is concentrated in the front part of the shoe as shown by the reproducible maximum found at locations 3–6. Generally, steel shoes exhibit a similar wear distribution with a pronounced maximum in the toe part. Similarly to 6a, Fig. 6 plots the wear measurements on Polka’s left front foot (foot 1). A maximum, even if slightly asymmetric, is also found in Fig. 6 (left forefoot) for shoes types M0, S0, S1 and S2. However, the type 2 (Fig. 1) also exhibits two additional maxima on the heel part (locations 2 and 7). The difference in wear distribution of shoes M0
for foot 1 (front) and foot 3 (hind) shows that the limb can affect the wear pattern. Two different wear patterns could be observed by optical microscopy in the front wear resistant section. One wear type had a ridged appearance and was found on the most external part of the section (zone A) where wear was usually much more severe. The other wear type observed in the internal area (zone B) as well as in the other wear resistant inserts revealed a rather featureless wear morphology. Corresponding SEM pictures are shown in Fig. 7. The ridged structure of zone A and the corresponding large smearing is clearly visible in Fig. 7a and b, respectively. Fig. 7c shows the typical morphology found in zone B characterised by cracks and debris up to 20 m in size. 4. Discussion The results show that the average wear of horseshoes is affected by several factors such as the horse and the horses leg. The horse plays a determining role: according to Figs. 4 and 5 Polka produces nearly twice so much wear than Quomètte for an equivalent walking distance on hard ground. Both horses exhibit significantly more wear on the hind feet than on the forefeet. A similar effect of horse and limb on shoe wear is generally observed with traditional steel horseshoes, although these observations are not corroborated by quantitative data.
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
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Fig. 4. Plot of the linear wear of the wear resistant sections versus distance as measured over four shoeing periods on horse Polka. M0 and S0 designate standard shoes with wear resistant section of thickness 2 and 5 mm, respectively. S1 and S2 correspond to S0 shoes with rear wear resistant sections structured with parallel grooves perpendicular to shoe symmetry axis (S1) or with cubic protuberances (S2).
Fig. 5. Plot of the linear wear of the wear resistant sections versus distance as measured over three shoeing periods on horse Quom`ette. M0 and S0 designate standard shoes with wear resistant section of thickness 2 and 5 mm, respectively. S2 corresponds to S0 shoes with rear wear resistant sections structured with cubic protuberances.
Within the limited experimental reproducibility, the structure and the thickness of the wear resistant inserts do not appear to play a relevant role on the wear intensity (Figs. 4 and 5). However, the structure of the wear inserts clearly affected the distribution of wear for one horse (Fig. 6). Mounted on Polka, the structure S2 exhibited a more homogeneous distribution of wear compared to other shoe types that, like steel shoes, wore predominantly in the front part (toe). Over a total of three horses shod with the S2 type,
the same effects were observed on only one horse than Polka, thus this observation could not be generalised. The effect of the S2 structure on the wear is likely related to a more uniform loading of the foot during gait. The reason for this is at present not clear. Particular frictional and dumping properties of the S2 structure could play a role here. The wear protective functionality of a shoe is in principle lost when the hoof becomes in direct contact with
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S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
Fig. 6. Normalised shoe wear at different locations on shoe. Data from four shoeing periods of horse Polka with the same type of shoes (M0 on hind foot 3) or with different structured types (M0, S0, S1 and S2 on front foot 1).
the ground and even if this happens only locally. Thus by constant average wear rate the functionality of S2 type structured horseshoes on certain horses is conserved for a longer time because wear is distributed more homogeneously. An interesting point is that wear seems to be mostly affected by the distance run during promenades in the field as suggested by the linear proportionality found in Figs. 4 and 5. The reason for this is probably related to the harder ground found in this activity compared to the sawdust and wood chips used for horse dedicated facilities such as the carrousel, training field and the horsemanship. The fact that no significant wear or damage was observed during periods where no promenades took place corroborates the conclusion that promenades are at the origin of wear. Interestingly, good reproducibility of wear distribution is found while large scatter in wear-distance curves is observed. This indicates that scatter is not a consequence of a lack of precision in the measurement of wear but rather, is related to shortcomings in the activity control. In effect it is likely that the degree of wear varies with weather conditions (wet or dry conditions, ground temperature) and with the state of the ground (presence of earth detritus, vegetation). The investigation was carried out over a period of nearly nine consecutive months where weather and ground conditions varied considerably. A more detailed monitoring of the ground and weather con-
ditions is needed to improve the reliability of field investigation of horseshoes wear. The observed wear morphologies can be compared to published works on wear of elastomers. Schweitz and Ahman [3] observed specific wear patterns consisting in a ridged “stormy sea”-like morphology and in extended polymer smearing for rubber sliding/rolling on steel. Such features are evident in Fig. 7a and b, thus suggesting that rolling/sliding determined wear in the front part of the horseshoe. This is consistent with the known hoof kinematics [4]. At slow walk, the foot usually contacts the surface over the whole bearing edge of the hoof nearly simultaneously. As the walk speeds up and/or the horse shifts to faster gait the hoof motion become more complex and involves a rotation. The heel impacts first and subsequently the foot is rotated with the load being transmitted first to the quarters and finally, during the lift-off phase, to the toe. The latter regions experience more severe rolling/sliding conditions and larger forces than the heels. The rear part of the central insert exhibited a similar morphology and detached fragments sizes as reported by Schweitz and Ahman [3] for the general appearance of complex sliding abrasion of rubber. Although such comparisons are somehow speculative and need to be substantiated with additional experimental evidence, these observations suggest that a polymer with increased resistance against
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
1305
5. Conclusions A quantitative methodology to investigate the wear phenomena occurring on horseshoes was developed and successfully applied in a field investigation of polymer horseshoes. Results shows that, for a given horse, shoe wear depends essentially on the cumulative distance run on hard grounds such as asphalt and concrete. The wear rate varies significantly among different horses and between forefeet or hind feet. Wear was generally more pronounced on the front part of the horseshoes. However, for certain horses, slight modifications of the shoe structure lead to an homogeneous re-distribution of wear around shoe without affecting the overall amount of wear. Thus, optimised shoe structures have potential to increase product lifetime. Mechanisms contributing to polymer wear could be attributed to combined rolling/sliding and to abrasion by analogy to wear patterns observed on elastomers after well-defined laboratory wear tests. As a general conclusion, this work has shown that a simple scientific approach to the complex topic of horseshoes wear can lead to a better understanding of the involved mechanisms and to the identification of factors determining the resistance to wear. A precise monitoring of the ground and weather conditions is recommended to verify the role of these factors on wear of polymer horseshoes.
Acknowledgements The authors thank HippoDynamix AG, Watt/Zürich for the financial support and for providing all the material as well as veterinary expertise. Acknowledgements to Mrs. N. Manigley, La Sarraz and to M.J.-D. Richard, Cronay for their readiness to test the shoes on their horses and to precisely record the horse activity. The farriers M.D. Schlaefli, Champvent and M.T. Raval, Grandvaux are acknowledged for their help and for their useful suggestions and comments. References Fig. 7. SEM images of the central wear resistant section after 56 days of shoeing on Polka, foot 1. (a and b) Severe wear area (zone A, external part) and (c) mild wear area (zone B, internal part).
rolling/sliding wear would be beneficial for this type of application.
[1] W. Moyer, J.P. Anderson, J. Am. Vet. Med. Assoc. 166 (1975) 49–52. [2] I. Anich, Ch. Stanek, Ch. Hinterhofer, Pferdeheilkunde 14 (1998) 469–477. [3] J.A. Schweitz, L. Ahman, in: K. Friedrich (Ed.), Friction and Wear of Polymer Composites, Elsevier, Amsterdam, 1986, pp. 289–327. [4] J. Rooney, Online J. Vet. Res. 4 (1999) 73–93, http://www.Cpb. ouhsc.edu/OJVR/jvet196a.htm.
Case study
Wear of polymer horseshoes: a field investigation S. Mischler a,∗ , M. Hofmann b a
Chemin des Bosquets 2c, CH-1315 La Sarraz, Switzerland b MatSearch, 1009 Pully, Switzerland
Abstract A methodology to monitor wear behaviour of polymer horseshoes was developed and applied in a field investigation. Results show that wear is proportional to the distance run on hard grounds while other typical horse activities performed on softer grounds do not contribute significantly to degradation. Slight modifications of the shoe structure affect the distribution of wear on the shoe sole and may thus increase the lifetime. The method allowed one to quantitatively describe differences in wear behaviour among individual horses. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Wear; Horseshoe; Polymer; Field test
1. Introduction Horseshoes can affect both the foot and the entire limb [1]. The solicitation of horseshoes has changed during the time from tracks across the field to roads covered with more abrasive gravel or asphalt. The steel shoe fills an important function as it protects the hoof against wear or damage during locomotion, but it limits the shock absorbing properties and the flexibility of the hoof. It interferes with the hoof mechanism, i.e. the complex sequence of hoof deformations occurring during gait to adsorb the shock and to enhance blood circulation, hence nutrition and quality of the hoof, and therefore can increase the risk of injuries. In recent years there was a considerable development in the field of horseshoes using light materials, such as aluminium matrix composites or polymer, as alternative to the traditional steel. It was previously observed that the use of aluminium matrix composites was not a valid alternative for riding horses because of massive wearing and breakage [2]. Polymer materials having higher elasticity offer higher damping properties and an enhanced capacity of the shoes to fit the natural deformation of the hoof occurring during gait. These advantages result in a better compatibility with the hoof mechanism and a smaller solicitation of the articulations finally contributing to the wellbeing of the horse. The main shortcoming encountered when using polymers as horseshoes material lies in the intrinsic limited resistance to wear compared to steel. Normally, horses are shod every 6–10 weeks and during this shoeing period the horseshoe ∗ Corresponding author. Tel.: +41-21-866-6711; fax: +41-21-866-6711. E-mail address: [email protected] (S. Mischler).
must withstand the severe mechanical and abrasive solicitation induced by the horse activity. In many cases, even steel shoes cannot hold the required lifetime because of severe wear of the shoe. Therefore, there is a strong need to better control wear of polymer horseshoes and to develop criteria allowing one to predict their useful lifetime as a function of field conditions. The present work was initiated to develop a method to quantify wear of polymeric horseshoes and to identify critical field conditions as well as others design factors influencing wear. For this, commercial polymer horseshoes were evaluated in a dedicated field test involving nine horses active in riding schools for a total of 26 shoeing periods. The activity of the horses was monitored and wear of the horseshoe sole was measured at regular intervals during each shoeing period as well as after removal. Optical and electronic microscopy was used to identify relevant wear mechanisms. The influence of slight modifications of the shoe structure on the wear behaviour was also evaluated. 2. Experimental The polymer horseshoes used in the presented study were produced by the company HippoDynamix and are shown in Fig. 1. They consist in a two part transparent base shaped in form of a traditional horseshoe, with a bridge connecting the two ends. The base contains the nail slots to fix the shoe on the hoof with steel nails. In selected locations, wear resistant sections were inserted by co-injection that can support additional inserts and spikes for winter time riding. The base is made out of commercial polyurethane of 72 Shore
0043-1648/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0043-1648(03)00166-2
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
D hardness and the wear resistant inserts are made out of softer elastomer like polyurethane of 91 Shore A hardness (all data according to manufacturers). The polyurethane base is rigid so that it can be easily nailed and filed to fit the shoe to the hoof. The thickness of the base was 12 mm for the horseshoe sizes 130 and 140 while, for size 150, the thickness was 14 mm. Two standard horseshoe models, M0 and S0, were used: they differed in the profile height of the wear resistant inserts, either 2 mm (M0) or 5 mm (S0). The total surface of the wear resistant inserts increased with increasing horseshoe size and corresponded to approximately 40 cm2 for size 140. On some shoes, the standard wear resistant inserts situated backwards near to the heel region of the shoe were machined to provide a structured profile intended to improve flexibility and adhesion on soft grounds. Two types of structure were considered: structure S1 consisted in a number of parallel grooves (3 mm in width and depth) machined perpendicular to the shoes’ symmetry axis at a intervals of 3 mm while cubic protuberances (3 mm dimension) characterised structure S2 as shown in Fig. 1. Wear was quantified by measuring the dimensional change of the base and of the wear resistant inserts. The thickness changes of the base as well as the wear resistant inserts with respect to the base were measured in eight positions distributed on the horseshoes (Fig. 2). The difference with respect to the thickness values of a new horseshoe corresponds to wear. For each location, the wear of the base was added to the change in profile height of the wear resistant inserts to compensate for wear of the base. Shoe thickness was measured before and after removal from the horse and, for control purposes, at regular intervals during utilisation. In the latter case, only profile changes were considered. All
1301
Fig. 2. Location of measured points (crosses) on the horseshoe sole for the determination of wear in wear resistant inserts.
dimensional measurements were carried out using an electronic caliper (Tesa Digit Cal) characterised by a repeatability of 0.01 mm. However, because of uncertainties in the exact positioning of the instrument on the horseshoes, measurement repeatability was ±0.1 or ±0.2 mm for measurement after removal and during utilisation, respectively. All the horses were shoed by the same farrier after preparing the hoof to correctly fit the horse anatomy. Feet were numbered with the numbers 1, 2, 3 and 4 for the forefoot left, forefoot right, hind left and hind right, respectively. The typical weekly activity of the horses consisted in: 6 h of carrousel (ground: wood chips mixed with sand), 1 h of horsemanship (ground: sawdust) and 2 h training (ground: wood chips). In addition, depending on weather conditions, horse weekly activity included 3–6 promenades. Typically, a promenade lasted 1 h during which the horse may walk, trot, canter, and gallop for 4–5 km on hard ground (asphalt or concrete) and an equivalent distance on mixed ground earth/stones. Variations in the weekly activity were monitored and the total distance travelled recorded. At regular intervals of 1 or 2 weeks each horseshoe was observed, photographed and measured. No steel controls were used.
3. Results
Fig. 1. Polymer horseshoe mounted on left hind foot. The rear part (top of the picture) exhibits a S2 type structure. (1) Transparent base, (2) bridge, (3) nail slots and (4) wear resistant inserts.
Although nine horses were objects of the investigation for 26 shoeing periods, only results for two horses, Polka (female, Swiss half breed, 500 kg) and Quomètte (female, French half breed, 500 kg) will be presented here because they were shod the most with the polymer products under study. The consequence of wear is illustrated in Fig. 3, where a new shoe is compared to a horseshoe used for 52 days on Polka. Although the shoe is still functional after 52 days, large wear is observed in particular in the front part (toe).
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S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
Fig. 3. Horseshoes of size 130 with 2 mm thick wear resistant sections (M0). (a) Unused and (b) after 52 days of use.
In the case of Polka, large wear was observed even with traditional steel shoes. The average wear, i.e. the average value of reduction in profile measured on the eight positions shown in Fig. 2 is plotted in Figs. 4 and 5 against the total distance travelled during promenades. Despite large scatter in the data, some proportionality between wear and distance can be observed in Fig. 5 regardless of the shoe type. In the case of Quomètte (Fig. 5) the reduced number of experimental points does not provide sufficient evidence of proportionality between wear and distance run. The normalised wear was calculated by dividing the wear measured at each location by the highest value observed, and this for each shoe. By plotting the normalised wear as a function of the measurement location, one obtains the wear distribution profiles shown in Fig. 6 for selected shoes. Fig. 6 shows the wear distribution measured on Polka, left hind foot (foot 3), for four shoeing periods with the same horseshoe type (M0). Wear is concentrated in the front part of the shoe as shown by the reproducible maximum found at locations 3–6. Generally, steel shoes exhibit a similar wear distribution with a pronounced maximum in the toe part. Similarly to 6a, Fig. 6 plots the wear measurements on Polka’s left front foot (foot 1). A maximum, even if slightly asymmetric, is also found in Fig. 6 (left forefoot) for shoes types M0, S0, S1 and S2. However, the type 2 (Fig. 1) also exhibits two additional maxima on the heel part (locations 2 and 7). The difference in wear distribution of shoes M0
for foot 1 (front) and foot 3 (hind) shows that the limb can affect the wear pattern. Two different wear patterns could be observed by optical microscopy in the front wear resistant section. One wear type had a ridged appearance and was found on the most external part of the section (zone A) where wear was usually much more severe. The other wear type observed in the internal area (zone B) as well as in the other wear resistant inserts revealed a rather featureless wear morphology. Corresponding SEM pictures are shown in Fig. 7. The ridged structure of zone A and the corresponding large smearing is clearly visible in Fig. 7a and b, respectively. Fig. 7c shows the typical morphology found in zone B characterised by cracks and debris up to 20 m in size. 4. Discussion The results show that the average wear of horseshoes is affected by several factors such as the horse and the horses leg. The horse plays a determining role: according to Figs. 4 and 5 Polka produces nearly twice so much wear than Quomètte for an equivalent walking distance on hard ground. Both horses exhibit significantly more wear on the hind feet than on the forefeet. A similar effect of horse and limb on shoe wear is generally observed with traditional steel horseshoes, although these observations are not corroborated by quantitative data.
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
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Fig. 4. Plot of the linear wear of the wear resistant sections versus distance as measured over four shoeing periods on horse Polka. M0 and S0 designate standard shoes with wear resistant section of thickness 2 and 5 mm, respectively. S1 and S2 correspond to S0 shoes with rear wear resistant sections structured with parallel grooves perpendicular to shoe symmetry axis (S1) or with cubic protuberances (S2).
Fig. 5. Plot of the linear wear of the wear resistant sections versus distance as measured over three shoeing periods on horse Quom`ette. M0 and S0 designate standard shoes with wear resistant section of thickness 2 and 5 mm, respectively. S2 corresponds to S0 shoes with rear wear resistant sections structured with cubic protuberances.
Within the limited experimental reproducibility, the structure and the thickness of the wear resistant inserts do not appear to play a relevant role on the wear intensity (Figs. 4 and 5). However, the structure of the wear inserts clearly affected the distribution of wear for one horse (Fig. 6). Mounted on Polka, the structure S2 exhibited a more homogeneous distribution of wear compared to other shoe types that, like steel shoes, wore predominantly in the front part (toe). Over a total of three horses shod with the S2 type,
the same effects were observed on only one horse than Polka, thus this observation could not be generalised. The effect of the S2 structure on the wear is likely related to a more uniform loading of the foot during gait. The reason for this is at present not clear. Particular frictional and dumping properties of the S2 structure could play a role here. The wear protective functionality of a shoe is in principle lost when the hoof becomes in direct contact with
1304
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
Fig. 6. Normalised shoe wear at different locations on shoe. Data from four shoeing periods of horse Polka with the same type of shoes (M0 on hind foot 3) or with different structured types (M0, S0, S1 and S2 on front foot 1).
the ground and even if this happens only locally. Thus by constant average wear rate the functionality of S2 type structured horseshoes on certain horses is conserved for a longer time because wear is distributed more homogeneously. An interesting point is that wear seems to be mostly affected by the distance run during promenades in the field as suggested by the linear proportionality found in Figs. 4 and 5. The reason for this is probably related to the harder ground found in this activity compared to the sawdust and wood chips used for horse dedicated facilities such as the carrousel, training field and the horsemanship. The fact that no significant wear or damage was observed during periods where no promenades took place corroborates the conclusion that promenades are at the origin of wear. Interestingly, good reproducibility of wear distribution is found while large scatter in wear-distance curves is observed. This indicates that scatter is not a consequence of a lack of precision in the measurement of wear but rather, is related to shortcomings in the activity control. In effect it is likely that the degree of wear varies with weather conditions (wet or dry conditions, ground temperature) and with the state of the ground (presence of earth detritus, vegetation). The investigation was carried out over a period of nearly nine consecutive months where weather and ground conditions varied considerably. A more detailed monitoring of the ground and weather con-
ditions is needed to improve the reliability of field investigation of horseshoes wear. The observed wear morphologies can be compared to published works on wear of elastomers. Schweitz and Ahman [3] observed specific wear patterns consisting in a ridged “stormy sea”-like morphology and in extended polymer smearing for rubber sliding/rolling on steel. Such features are evident in Fig. 7a and b, thus suggesting that rolling/sliding determined wear in the front part of the horseshoe. This is consistent with the known hoof kinematics [4]. At slow walk, the foot usually contacts the surface over the whole bearing edge of the hoof nearly simultaneously. As the walk speeds up and/or the horse shifts to faster gait the hoof motion become more complex and involves a rotation. The heel impacts first and subsequently the foot is rotated with the load being transmitted first to the quarters and finally, during the lift-off phase, to the toe. The latter regions experience more severe rolling/sliding conditions and larger forces than the heels. The rear part of the central insert exhibited a similar morphology and detached fragments sizes as reported by Schweitz and Ahman [3] for the general appearance of complex sliding abrasion of rubber. Although such comparisons are somehow speculative and need to be substantiated with additional experimental evidence, these observations suggest that a polymer with increased resistance against
S. Mischler, M. Hofmann / Wear 255 (2003) 1300–1305
1305
5. Conclusions A quantitative methodology to investigate the wear phenomena occurring on horseshoes was developed and successfully applied in a field investigation of polymer horseshoes. Results shows that, for a given horse, shoe wear depends essentially on the cumulative distance run on hard grounds such as asphalt and concrete. The wear rate varies significantly among different horses and between forefeet or hind feet. Wear was generally more pronounced on the front part of the horseshoes. However, for certain horses, slight modifications of the shoe structure lead to an homogeneous re-distribution of wear around shoe without affecting the overall amount of wear. Thus, optimised shoe structures have potential to increase product lifetime. Mechanisms contributing to polymer wear could be attributed to combined rolling/sliding and to abrasion by analogy to wear patterns observed on elastomers after well-defined laboratory wear tests. As a general conclusion, this work has shown that a simple scientific approach to the complex topic of horseshoes wear can lead to a better understanding of the involved mechanisms and to the identification of factors determining the resistance to wear. A precise monitoring of the ground and weather conditions is recommended to verify the role of these factors on wear of polymer horseshoes.
Acknowledgements The authors thank HippoDynamix AG, Watt/Zürich for the financial support and for providing all the material as well as veterinary expertise. Acknowledgements to Mrs. N. Manigley, La Sarraz and to M.J.-D. Richard, Cronay for their readiness to test the shoes on their horses and to precisely record the horse activity. The farriers M.D. Schlaefli, Champvent and M.T. Raval, Grandvaux are acknowledged for their help and for their useful suggestions and comments. References Fig. 7. SEM images of the central wear resistant section after 56 days of shoeing on Polka, foot 1. (a and b) Severe wear area (zone A, external part) and (c) mild wear area (zone B, internal part).
rolling/sliding wear would be beneficial for this type of application.
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