EP4631381A1

EP4631381A1 - Improved fit strap shoe and process for making a strap shoe

Info

Publication number: EP4631381A1
Application number: EP25168308.2A
Authority: EP
Inventors: Beata PANCIOVA; Paolo Rossin
Original assignee: Erregi Srl
Current assignee: Erregi Srl
Priority date: 2024-04-12
Filing date: 2025-04-03
Publication date: 2025-10-15

Abstract

The present invention relates to a strap shoe, such as an ankle strap, a gladiator strap or a foot strap, having an improved fit, comprising an upper (12), a bottom portion (11) to which the upper (12) is fastened, and a strap (14) connected to the bottom portion (11) and/or to the upper (12) and/or incorporated into at least one thereof (11, 12), for fastening the footwear to the foot and/or ankle of a user, and characterised in that the strap (14) comprises at least one strap portion made of a NiTi alloy comprising at least two zones (14a,14b) with different mechanical properties, in particular bending response mechanical properties. The present invention further relates to a process for making a strap shoe.

Description

TECHNICAL FIELD

The present invention relates to a strap shoe with an improved fit, such as a shoe with an ankle strap, with a gladiator strap or with a foot strap.

STATE OF THE ART

In the state of the art, it is well known to make shoes, in particular open shoes for summer use, with straps that fasten the shoe to the foot. In particular, the straps can be configured to wrap around the top of the foot, the ankle or even extend along the calf.
However, differences in the size and shape of feet and calves can make it difficult to find strap shoes that fit perfectly. It therefore often occurs that the shoes are uncomfortable, in particular when the strap is too loose or tight with respect to the shape of the foot, ankle or calf of the user.
If worn too tightly, the strap can cause blisters or abrasions as a result of foot movement; conversely, if worn too loosely, it does not allow the shoe to remain properly fastened to the foot, which can lead to unstable situations with consequent falls and/or injury by the user.
Moreover, the straps used in shoes today are easily and quickly subject to wear and tear. In fact, any elastic portions integrated in the strap to increase the wearing comfort thereof tend to quickly lose their initial elastic properties as they are subjected to constant stresses during use.

OBJECTS AND SUMMARY OF THE INVENTION

The problem underlying the present invention is to overcome the drawbacks of the prior art. In particular, within the scope of this problem, an aim is to design a strap shoe that is particularly comfortable in use.
Another aim of the present invention is to make a strap shoe that is effectively adaptable to the conformation of the user's foot, ankle and/or calf.
Still another aim of the present invention is to make a strap shoe that minimises stresses on the parts of the body with which it comes into contact, preventing any injuries due to rubbing.
A further aim of the present invention is to design a strap shoe that is particularly resistant to wear and tear and is able to maintain the initial wearing comfort over time.
Not least of the aims of the present invention is to devise a strap shoe trap that offers the user good stability without sacrificing a comfortable fit.
In accordance with a first aspect thereof, the invention therefore relates to a strap shoe comprising an upper, a bottom portion to which the upper is fastened, and a strap connected to the bottom portion and/or to the upper and/or incorporated into at least one thereof, for fastening the shoe to the foot and/or ankle of a user.
According to the present invention, the strap comprises at least one strap portion made of a nickel-titanium alloy, hereinafter also referred to as NiTi or Nitinol alloy, comprising at least two zones with different mechanical properties, in particular bending response mechanical properties.
The Applicant has devised making at least one shoe strap portion in a NiTi alloy with at least two zones behaving differently from a mechanical point of view and, in particular, from the point of view of bending response.
It is thereby possible to guarantee both the hold between the shoe and the foot, and at the same time to have a strap that has a sufficient deformation softness to facilitate the operations necessary to put the shoe on and not hinder the movement of the foot and ankle, thereby increasing the comfort of use of the shoe and, thanks to the properties of the NiTi alloy, maintaining it over time.
In accordance with a second aspect of the invention, the invention further relates to a process for making a strap shoe that comprises the steps consisting of:

providing a NiTi alloy semi-finished product with work hardening of at least 10%, preferably at least 30%, more preferably at least 50%;
carrying out a thermal pre-treatment to homogenise the microstructure of the semi-finished product through heating by Joule effect generated by a direct electric current passed through the semi-finished product itself;
thermoforming the semi-finished product to give a final shape to at least one strap portion of the strap shoe;
carrying out a thermal post-treatment through heating by Joule effect generated by a direct electric current applied to the at least a first zone of the strap portion and to the at least a second zone of the strap portion different from the first, wherein the direct electric current is applied to the at least a first zone with different operating parameters with respect to the direct electric current applied to the at least a second zone; and
fastening the strap to a bottom portion and/or to an upper of the strap shoe.

In the context of the present description and in the attached claims, "strap portion zone" is intended to indicate a sub-portion of the strap portion that does not comprise the entire strap portion itself.
Furthermore, within the scope of the present description and in the appended claims "different operating parameters with respect to the at least a second zone" is also intended to include the case where a zero direct electric current is applied to the at least a second zone.
Conveniently, the process for making at least one strap portion of a strap shoe achieves the same advantages as described with reference to a strap shoe according to the present invention.
Further features of the preferred embodiments of the device for transporting objects that can be converted into a workstation according to the present invention are the subject of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the appended drawings.
The different features in the individual configurations can be combined with each other as desired according to the following description, if the advantages resulting specifically from a particular combination are to be availed of.
In such drawings:

Figure 1 is a side elevation view of a first preferred embodiment of a strap shoe according to the present invention;
Figure 2 is a bending response curve of a first variant of a strap portion of a shoe according to the invention;
Figure 3 is a side elevation view of a second preferred embodiment of a strap shoe according to the present invention;
Figure 4 is a schematic representation of a strap portion of the shoe of Figure 3;
Figure 5 is a side elevation view of a third preferred embodiment of a strap shoe according to the present invention;
Figure 6 is a side elevation view of a fourth preferred embodiment of a strap shoe according to the present invention; and
Figure 7 is a side elevation view of a fifth preferred embodiment of a strap shoe according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

For the illustration of the drawings, use is made in the following description of identical numerals or symbols to indicate construction elements with the same function. Moreover, for clarity of illustration, certain references may not be repeated in all drawings.
While the invention is susceptible to various modifications and alternative constructions, certain preferred embodiments are shown in the drawings and are described hereinbelow in detail. It must in any case be understood that there is no intention to limit the invention to the specific embodiment illustrated, but, on the contrary, the invention intends covering all the modifications, alternative and equivalent constructions that fall within the scope of the invention as defined in the claims.
The use of "for example", "etc.", "or" indicates non-exclusive alternatives without limitation unless otherwise indicated. The use of "comprises" and "includes" means "comprises or includes, but not limited to", unless otherwise indicated.
With reference to Figure 1, a first preferred embodiment of a strap shoe according to the present invention is illustrated, overall indicated with 10.
In the context of the present description and the appended claims, the term "strap shoe" is intended to indicate any type of open or closed shoe provided with a strap for fastening the shoe to the foot or ankle of the user, such as ballerinas with strap, classical women's shoes with strap, sandals with strap, mules with strap, etc. In general, a strap shoe comprises three main elements: an upper, a bottom portion to which the upper is fastened and which comprises an insole and a sole, and a strap connected to the upper or incorporated therein, for fastening the shoe to the user's foot and/or ankle.
The upper of the strap shoe can comprise side parts, a heel part and a toe part. The upper of the shoe is often formed by a plurality of material elements (e.g. fabrics, layers of polymer sheets, foamed or otherwise, leather, synthetic leather) that are sewn or glued together to delimit a space within the shoe configured to comfortably and securely accommodate a foot. In particular, the upper forms a structure that can extend over one or more of the following areas of the foot: instep, toe, lateral sides, medial side and heel.
The shoe comprises an opening for the entry and removal of the foot from the space defined inside the upper, which extends from the heel portion of the upper.
The shoe 10 in Figure 1 comprises a bottom 11 and an upper 12 attached to the bottom of the shoe. The upper 12 comprises a toe part 122 and a heel part 123 joined or connected to each other by lateral portions 121 to form a peripherally closed structure. The parts of the upper 12 define, in a position opposite the bottom 11, an opening 13 for the entry and exit of the foot. The upper 12 and the bottom 11 define a housing configured to accommodate a user's foot. A strap 14 is fastened to the upper 12, which in the embodiment of Figure 1, is connected thereto by means of a loop 124 made at the heel part 123. In the embodiment of Figure 1, a heel 15 is applied to the bottom 11.
The strap 14 comprises at least one strap portion made of a nickel-titanium alloy, hereinafter also referred to as NiTi or Nitinol alloy, having a percentage weight composition (%) of the alloy between Ni(46%)Ti(54%) (w:w) and Ni(55%)Ti(45%); preferably, Ni(51%)Ti(49%) (w:w) and Ni(50.8%)Ti(49.2%) (w:w).
According to the present invention, the at least one strap portion comprises at least two zones 14a,14b with different mechanical properties, in particular bending response mechanical properties.
By way of example, the strap 14 of the shoe in Figure 1 is made entirely of NiTi alloy and comprises at least two zones 14a,14b with different bending response mechanical properties.
Alternatively, the strap 14 can have at least one portion made of a NiTi alloy with at least two zones 14a,14b with different bending response mechanical properties, or comprise a core 141 (shown diagrammatically in Fig. 4) of which at least one portion is made of such a NiTi alloy with at least two zones 14a,14b with different bending response mechanical properties.
In general terms, a NiTi alloy can have either a bending response mechanical behaviour characterised by a sharply flag-shaped bending response curve, indicative of a substantially pure pseudo-elastic mechanical behaviour, or a quasi-linear behaviour with hysteresis, i.e. an intermediate or combined behaviour between a perfectly linear behaviour, typical for example of steel, and a substantially pure pseudo-elastic behaviour.
In the context of the present description and in the appended claims, "bending response mechanical properties with quasi-linear behaviour with hysteresis" is intended to indicate mechanical properties characterised by a bending response curve having a non-zero slope plateau and in any case less than a characteristic elastic deformation slope of steel, hereinafter also only "characteristic slope", e.g. greater than at least 10% and less than 85% of the characteristic slope.
In the context of the present description and the appended claims, "bending response mechanical properties with essentially pure pseudo-elastic behaviour" is intended to indicate mechanical properties characterised by a bending response curve with an essentially zero slope plateau, e.g. below 10% of the characteristic slope.
In the context of the present description and in the appended claims, "plateau" is intended to indicate a curve section with a lower slope with respect to a previous section, for example a first section with a slope reduced by at least 10% with respect to a slope of a second previous section.
According to a first variant of the at least one strap portion, the at least two zones 14a,14b with different bending response mechanical properties both have a quasi-linear behaviour with hysteresis, albeit different from one zone to the other.
Figure 2 shows the bending response curves 20 of a strap portion 14 comprising two zones 14a,14b with different mechanical properties according to the first variant, characterised through a temperature-controlled single cantilever bending test with reference to the ASTM F2516 | Metals | Tension Testing standard, in which the characteristic slope of the elastic deformation corresponds to a modulus of approximately 70GPa.
In particular, the strap portion made of NiTi alloy comprises at least a first zone 14a with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, so as to ensure the hold between the shoe and the foot, and at least a second zone 14b with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour, so as to give the second zone sufficient deformation softness to facilitate the operations necessary to put the shoe on and not hinder the movement of the foot and the ankle.
Within the context of the present description and the appended claims, with the relative expression "closer", a comparison between zones with different bending response mechanical properties identifiable within the strap portion is implied.
The strap portion comprising at least two zones 14a,14b with different bending response mechanical properties is characterised by a bending response represented by a curve 20 with at least two curve sections 21,22 with different trends, each representing the points at which bending is concentrated.
According to the first variant of the at least one strap portion, each section 21,22 of the bending response curve given by the strap portion 14 has a nearly linear behaviour with hysteresis, each characterised by a different plateau slope.
In any case, the plateau slope of each curve section 21,22 is between 85%-10% of the characteristic slope of an elastic deformation, such as the characteristic deformation of steel, which always has a linear trend, without any kind of plateau. In other words, the trend of each section 21,22 of the bending response curve given by the strap portion 14 according to the first variant corresponds to deformation with martensite induction.
In particular, two different responses are evident in Figure 2, both with pseudo-elasticity combined with linear elasticity, but at different loads and deformations corresponding to a differentiated response in two zones 14a, 14b of the material. Furthermore, hysteresis is present, characteristic of pseudo-elasticity, with complete recovery after a few cycles of settling a linear deformation.
In detail, a first curve section 21 representative of the first zone 14a with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a linear behaviour has a plateau slope lower than the characteristic slope, but still more than 50% of such characteristic slope, more preferably between 60%-85% of the characteristic slope, more preferably between 65%-80% of the characteristic slope.
Furthermore, a second curve section 22 representative of the second zone 14b with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a pseudo-elastic behaviour has a plateau slope between 20%-50% of the characteristic slope, preferably between 25%-45% of the characteristic slope, more preferably between 30%-40% of the characteristic slope.
The different mechanical properties mentioned above, i.e. the different properties of pseudo-elasticity combined with linear elasticity according to the first variant of the at least one strap portion 14, can be obtained through a thermoforming process of a NiTi alloy semi-finished product, which comprises the following steps:

providing a highly work hardened NiTi alloy semi-finished product (e.g. work hardened by at least 10%, preferably by at least 20%, more preferably by at least 30%, even more preferably by at least 40% or 50%) or performing a work hardening step (e.g. by at least 10%, preferably by at least 20%, more preferably by at least 30%, even more preferably by at least 40% or 50%) of a NiTi alloy semi-finished product by cold processing, such as rolling or drawing, in the absence of intermediate tempering heat treatments;
carrying out a thermal pre-treatment step to homogenise the microstructure of the semi-finished product, where the thermal pre-treatment step consists of heating by Joule effect generated by a direct electric current that is passed through the semi-finished product itself; and
a thermoforming step to give the final shape (or "shape setting" step) of the strap portion, e.g. by treatment in an oven.

By way of example, in the process described above, the starting NiTi alloy semi-finished product is a wire. The wire can be purchased already in the desired work-hardened state (Cold Worked or As Drawn) or be subjected to the above-mentioned work-hardened phase after a short heat treatment (Straight Annealed). By way of example, the wire is a wire with a round cross-section with a thickness (diameter) between 0.10 mm and 30 mm; between 0.10 mm and 10 mm; between 0.20 mm and 9 mm; between 0.30 mm and 8 mm; between 0.40 mm and 7 mm; between 0.50 mm and 6 mm; between 0.60 mm and 5 mm; between 0.70 mm and 4 mm; between 0.80 mm and 3 mm; other values not specifically comprised in the above list are however freely possible depending on processing requirements and, of course, also form part of the present invention. In another example, the wire is a wire with a square cross-section with sides between 0.10 mm x 0.10 mm and 5 mm x 5 mm; preferably, between 0.20 mm x 0.20 mm and 2 mm x 2 mm. Or, the wire is a wire with rectangular cross-section with sides between 0.10 mm x 0.15 mm and 0.15 mm x 30 mm. As for the possible lengths, they are freely variable and/or selectable depending on the final shape of the desired strap portion.
A direct electric current is then passed through the wire (thermal pre-treatment step) applying a voltage averaging between 3 volt and 180 volt; between 10 volt and 150 volt; between 20 volt and 100 volt; preferably, between 30 volt and 90 volt; more preferably, between 40 volt and 80 volt. The intensity of the applied electric current depends on the dimensions of the semi-finished product, e.g. preferably the length of the wire. For example, to obtain a shoe strap 14, it is preferable to use a direct current between 0.2 ampere and 15 ampere; between 0.3 and 10 ampere; between 0.4 ampere and 5 ampere; between 0.4 ampere and 4 ampere; preferably between 0.4 ampere and 3 ampere; even more preferably between 0.5 ampere and 2 ampere, applying it for a time between 3 and 10 seconds, preferably between 4 and 9 seconds, more preferably between 5 and 8 seconds, or between 5 and 10 seconds, depending on the thickness and length of the wire.
For a wire with a thickness of 1 mm and a length of 50-100 cm, for example, a voltage between 40 V and 80 V and a current intensity from 0.5 to 3 ampere is applied for times of 5-10 sec.
If necessary, the first thermal treatment step can also be carried out alternating with traditional treatment phases, such as rolling and/or drawing, in order to optimise the microstructure, eliminating work hardening defects and the possibility of breaking the material.
The thermal pre-treatment step is followed by the thermoforming step for achieving the desired final "shape-setting", for example, by carrying out a thermal treatment in an electric oven with the use of suitable jigs or moulds, to give the semi-finished product obtained in the thermal pre-treatment step the shape/form of the desired strap portion to be made. By way of example, the thermoforming step is carried out in an electric metal-forming oven with a refractory material mouth at a temperature between 200 °C and 650 °C, preferably between 470 °C and 530 °C, depending on the size of the mould and the thickness and length of the wire, for a period of time between 5 to 120 minutes, preferably between 15 to 40 minutes.
According to the present invention, the thermoforming step is followed by a further thermal treatment (post-treatment), carried out through heating by Joule effect generated by a direct electric current that is applied to specific zones of such a semi-finished product.
By way of example, the further thermal treatment is carried out by passing a direct current with a voltage from 40 V to 80 V (current intensity from 0.5 to 3 ampere) for times of 5-10 sec in a first zone of the strap portion to obtain the at least one zone 14a with bending response mechanical properties with near-linear behaviour with hysteresis close to a linear behaviour. Such a step is carried out by applying the electrodes of a voltage generator to the ends of the first zone.
Similarly, the further thermal treatment is carried out by passing a direct current with a voltage from 40 V to 80 V (current intensity from 0.5 to 3 ampere) for times of 15-20 sec in a second zone of the strap portion to obtain the at least a second zone 14b with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a pseudo-elastic behaviour. Such a step is carried out by applying the electrodes of a voltage generator to the ends of the second zone.
Thereby, the further thermal treatment is carried out only at one or more given zones of the already thermoformed semi-finished product to form the strap 14 or a portion thereof so that the strap portion has different bending response mechanical properties in different zones 14a,14b, i.e. a modular elasticity.
Thereby, it is advantageously possible to obtain a strap that has at least locally a pseudo-elasticity and deformation softness particularly suitable for the specific use to fasten a shoe to a user's foot or ankle without impeding the movement thereof and reducing abrasion in use, while at the same time guaranteeing an excellent hold of the strap on the shoe.
The strap, at least part of which is made of NiTi alloy obtained by the combined process described above, can express mechanical properties that vary depending on the geometry, but can also be modulated within the geometry itself, providing the mechanical response required for use as a shoe strap. In fact, the strap thus obtained has a very soft embrace, but at the same time offers a very firm hold on the shoe.
In the embodiment of Figure 1, the strap 14 is made entirely of a NiTi alloy in accordance with the first variant described above, having a first zone 14a close to the loop 124, preferably fastened thereto, with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, and a second zone 14b configured to rest against a part of the user's body, with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour.
In contrast, Figure 3 shows a second embodiment of a shoe 10 according to the invention with a strap 14 made in accordance with the first variant which differs from the first embodiment in that it has a plurality of straps 14. A first strap 14 is configured to fasten the shoe to the user's ankle, while the remaining straps are configured to rest against the user's instep.
Each strap 14 of the plurality of straps 14 is made with a liner 142 in which a core 141 is housed made of a NiTi alloy configured to give the strap 14 both elasticity properties and at the same time a high deformation softness. Thereby, the straps 14 are particularly comfortable, facilitating the movement of the ankle and foot without substantially stressing or rubbing against the parts of the body with which they interact.
Also in this case, the straps 14 comprise at least a first zone 14a bordering with and fastened to the upper 12 of the shoe which has bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, and at least a second zone 14b configured to rest against a part of the user's body, with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour.
Figure 5 shows a third embodiment of a shoe 10 with a strap 14 according to the present invention which differs from the first embodiment in that the strap 14 is configured to fasten the shoe to the user's heel. Also in this case, the strap 14 is made with a liner 142 in which a core 141 is housed made of a NiTi alloy configured to give the strap 14 both elasticity properties and at the same time a high deformation softness.
Furthermore, the strap 14 comprises at least a first zone 14a bordering with and fastened to the upper 12 of the shoe which has bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, and at least a second zone 14b configured to rest against a part of the user's body, with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour.
Figure 6 shows a fourth embodiment of a shoe 10 with a strap 14 according to the present invention which, similarly to the embodiment of Figure 3, has a plurality of straps 14 of which, a first sub-assembly is configured to fasten the shoe to the user's ankle, while a second sub-assembly of the plurality of straps 14 is configured to rest against the user's instep.
According to the invention, the at least one strap 14 of the plurality of straps comprises at least one portion made of a NiTi alloy, preferably configured to give the strap 14 both elasticity properties and at the same time high deformation softness.
In particular, the straps 14 comprise at least a first zone 14a bordering with and fastened to the upper 12 or to the bottom 11 of the shoe, which has bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, and at least a second zone 14b configured to rest against a part of the user's body, with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour.
In accordance with a second variant of the at least one strap portion 14 made of NiTi alloy, three zones 14a, 14b, 14c are provided with different bending response mechanical properties.
In particular, the strap portion made of NiTi alloy comprises a first zone 14a with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, a second zone 14b with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour, and a third zone 14c with bending response mechanical properties with substantially pure pseudo-elastic behaviour.
In terms of the bending response curve, the third zone 14c is represented by a third curve section (not illustrated) with a plateau slope trend less than 20% of the characteristic slope, preferably less than 15% of the characteristic slope, more preferably less than 10% of the characteristic slope. Such a range is therefore representative of pseudo-elasticity features that allow it to adapt to different limb sizes and always tighten at different openings with the same intensity, adhering well, but without exerting increasing or uncomfortable forces.
In particular, to make the third zone 14c, the thermoforming process of a semi-finished product made of a NiTi alloy requires that a direct current with a voltage of 40 V to 80 V (current intensity of 0.5 to 3 ampere) is passed through a zone of the strap portion for times of 21-25 sec during the thermal post-treatment step in order to obtain the third zone 14c with bending response mechanical properties with substantially pure pseudo-elastic behaviour. Such a step is carried out by applying the electrodes of a voltage generator to the ends of the third zone.
Figure 7 shows a fifth embodiment of a shoe 10 with a strap 14 according to the present invention using a strap having at least one portion obtained in accordance with the second variant.
The shoe 10 according to the fifth embodiment differs from the first embodiment in that the strap is fastened to the bottom 11 of the shoe 10, in particular to the heel 15 applied to the bottom 11. The strap 14 is configured to fasten the shoe to the user's ankle and has a liner 142 in which a core 141 made of a NiTi alloy is housed.
In particular, the strap 14 used in the shoe of the fifth embodiment comprises:

a first zone 14a bordering with and fastened to the bottom 11 of the shoe, in particular to the heel 15, which has bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour to ensure a stable and resistant fastening,
a second zone 14b configured to rest against the foot, with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour to adapt to the shape of the foot, but keep the shoe firm around the foot, and
a third zone 14c configured to wrap around the user's ankle/leg with bending response mechanical properties with essentially pure pseudo-elastic behaviour.

Thereby, while the third strap portion 14c makes it suitable for wrapping around the ankle and calf of the user, ensuring a high level of wearing comfort, the first portion 14a can be tightened around the heel 15, which has an invariable shape and size, locking in place. Thereby, the strap 14 can be made of the type that can be removed from the shoe 10.
The invention thus conceived is susceptible to modifications and variants, all falling within the same inventive concept. For example, the at least two zones 14a,14b,14c with different mechanical properties, in particular different bending response mechanical properties, can comprise any combination between a first zone with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a linear behaviour, a second zone with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a pseudo-elastic behaviour and a third zone with response mechanical properties with substantially pure pseudo-elastic behaviour.

Claims

Strap shoe (10) comprising
- an upper (12),

- a bottom portion (11) to which the upper (12) is fastened, and

- a strap (14) connected to the bottom portion (11) and/or to the upper (12) and/or incorporated into at least one thereof (11,12), for fastening the shoe to the foot and/or ankle of a user,
characterised in that the strap (14) comprises at least one strap portion made of a NiTi alloy comprising at least two zones (14a,14b) with different mechanical properties, in particular different bending response mechanical properties.
Strap shoe (10) according to claim 1, wherein the strap portion (14) comprising at least two zones (14a,14b) with different bending response mechanical properties comprises any combination of zones (14a,14b,14c) with mechanical properties, preferably different bending response mechanical properties, between:
- a first zone (14a) with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a linear behaviour,

- a second zone (14b) with bending response mechanical properties with quasi-linear behaviour with hysteresis close to a pseudo-elastic behaviour; and

- a third zone (14c) with bending response mechanical properties with essentially pure pseudo-elastic behaviour.
Strap shoe (10) according to claim 1 or 2, wherein the strap portion (14) comprising at least two zones (14a,14b) with different bending response mechanical properties is characterised by a bending response represented by a curve (20) with at least two curve sections (21,22) with different trends, preferably two curve sections (21,22) having different plateau slopes.
Strap shoe (10) according to claim 3, wherein the bending response curve (20) of the at least one strap portion (14) comprises any combination of curve sections (21,22) between:
- a first curve section (21) having a plateau slope lower than a characteristic slope of an elastic deformation and greater than 50% of such a characteristic slope, preferably between 60%-85% of the characteristic slope, more preferably between 65%-80% of the characteristic slope;

- a second curve section (22) having a plateau slope between 20%-50% of the characteristic slope, preferably between 25%-45% of the characteristic slope, more preferably between 30%-40% of the characteristic slope; and

- a third curve section having a plateau slope less than 20% of the characteristic slope, preferably less than 15% of the characteristic slope, more preferably less than 10% of the characteristic slope.
Strap shoe (10) according to claim 3 or 4, wherein each curve section (21,22) of the bending response curve given by the strap portion (14) has a trend corresponding to a trend of a deformation with martensite induction; and/or
wherein each curve section (21,22) of the bending response curve given by the strap portion (14) has a trend with quasi-linear behaviour with hysteresis.
Strap shoe (10) according to any one of the preceding claims, wherein the at least two zones (14a,14b) of the strap portion (14) with different mechanical properties from each other both have a quasi-linear behaviour with hysteresis, the quasi-linear behaviour with hysteresis being different between a first (14a) and a second (14b) zone of the at least two zones.
Strap shoe (10) according to any one of the preceding claims, wherein the at least one strap portion made of a NiTi alloy comprises three zones (14a,14b,14c) with different bending response mechanical properties, preferably a first zone (14a) with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a linear behaviour, at least a second zone (14b) with bending response mechanical properties with quasi-linear behaviour with hysteresis closer to a pseudo-elastic behaviour, and at least a third zone (14c) with bending response mechanical properties with substantially pure pseudo-elastic behaviour.
Strap shoe (10) according to any one of the preceding claims, wherein the strap (14) is of the type which is removable from the bottom portion (11) and/or from the upper (12).
Strap shoe (10) according to any one of the preceding claims, wherein a percentage weight composition (%) of the NiTi alloy in which the at least one strap portion (14) is made is between Ni(46%)Ti(54%) (w:w) and Ni(55%)Ti(45%) (w:w).
Process for making a strap shoe (10) according to any one of the preceding claims, comprising the steps of:
- providing a NiTi alloy semi-finished product with work hardening of at least 10%, preferably at least 30%, more preferably at least 50%;

- carrying out a thermal pre-treatment to homogenise the microstructure of the semi-finished product through heating by Joule effect generated by a direct electric current passed through the semi-finished product itself;

- thermoforming the semi-finished product to give a final shape to at least one strap portion (14) of the strap shoe (10);

- carrying out a thermal post-treatment through heating by Joule effect generated by a direct electric current applied to the at least a first zone (14a) of the strap portion (14) and to the at least a second zone (14b) of the strap portion (14) different from the first (14a), wherein the direct electric current is applied to the at least a first zone (14a) with at least one different operating parameter with respect to the direct electric current applied to the at least a second zone (14b); and

- fastening the strap (14) to a bottom portion (11) and/or to an upper (12) of the strap shoe (10).
Process according to claim 10, wherein the step of thermal post-treatment by Joule effect comprises applying to the at least a first zone (14a) of the strap portion (14) a potential difference with a voltage of 40 V to 80 V and/or a direct current with intensity between 0.5 and 3 Ampere, for times between 5 and 10 seconds.
Process according to claim 10 or 11, wherein the step of thermal post-treatment by Joule effect comprises applying to the at least a second zone (14b) of the strap portion (14) a potential difference with a voltage of 40 V to 80 V and/or a direct current with intensity between 0.5 and 3 Ampere, for times between 15 and 20 seconds.
Process according to any one of claims 10 to 12, wherein the step of thermal post-treatment by Joule effect comprises heating by Joule effect generated by a direct electric current at least a third zone (14c) of the strap portion (14) different from the first (14a) and the second (14b), wherein the direct electric current is applied to the at least a third zone (14a) with at least one different operating parameter with respect to the direct electric current applied to the at least a first (14a) and/or the at least a second (14b) zone.
Process according to claim 13, wherein the step of thermal post-treatment by Joule effect comprises applying to the at least a third zone (14c) of the strap portion (14) a potential difference with a voltage of 40 V to 80 V and/or a direct current with intensity between 0.5 and 3 Ampere, for times between 21 and 25 seconds.
Process according to any one of claims 10 to 14, wherein the steps of applying a potential difference to a zone (14a, 14b, 14c) of the strap portion (14) comprises applying the electrodes of a voltage generator to the ends of the zone (14a, 14b, 14c).