A multi-dimensional constrained thermally induced stress power generation unit

Abstract

The application discloses a multi-dimensional constraint thermal stress power generation unit, and belongs to the technical field of solid-state power generation. The power generation unit comprises a core working body, an external constraint structure and a piezoelectric ceramic array. The core working body is made of a solid material with thermal deformation characteristics, and can be configured as a one-dimensional line, a two-dimensional surface or a three-dimensional body according to its shape and mechanical characteristics. The external constraint structure is arranged along at least one direction of the core working body, and constrains the deformation and converts it into extrusion pressure fluctuation of the piezoelectric ceramic array. The core working body and the external constraint structure jointly apply a basic pre-tightening force, and ensure that the piezoelectric ceramic is always in a pure compression state in the whole working cycle. The application breaks the single dependence on three-dimensional volume expansion in the traditional scheme, expands the available working dimension from block compression to sheet bending and fiber tension, and greatly widens the range of selected materials.

Description

Technical Field

[0001] This invention belongs to the field of solid-state power generation technology, specifically relating to a device for generating electricity using the thermal deformation characteristics of solid materials, and more particularly to a power generation unit that converts the thermal deformation of materials into continuous extrusion pressure on piezoelectric ceramics through a constraint structure. Background Technology

[0002] The idea of ​​generating electricity using the thermal deformation of materials has been around for a long time. Traditional technological approaches almost all follow the same paradigm: selecting solid materials with a high coefficient of thermal expansion, causing them to expand in volume when heated, thereby pushing elastic components or directly compressing piezoelectric elements to perform work.

[0003] However, this paradigm faces a material selection dilemma rooted in the laws of solid-state physics in engineering practice. The work-performing material must simultaneously meet several mutually restrictive indicators: first, it must possess a high elastic modulus to ensure sufficiently high thermal stress under constrained conditions; second, it must possess a high coefficient of thermal expansion to ensure effective deformation within a limited temperature rise; third, it must possess a low specific heat capacity to achieve a greater temperature rise and faster thermal response under the same heat input; and fourth, it must possess high thermal conductivity to shorten the time it takes for heat to penetrate from the outer surface to the interior of the material, supporting higher cycling frequencies.

[0004] These indicators are not independent of each other. Solid thermal expansion stems from the anharmonic effect of interatomic potential energy—the interatomic distance increases with increasing temperature. The Georgysen parameter, characterizing the degree of anharmonicity, links the coefficient of thermal expansion, bulk modulus, density, and specific heat capacity through inherent laws. Within this framework, materials with a high coefficient of thermal expansion often also have a correspondingly high specific heat capacity, resulting in a large amount of heat being consumed by lattice vibrations rather than being converted into effective stress fluctuations. At the same time, materials with high elastic modulus and high strength often have strong interatomic bond energies and typically have a low coefficient of thermal expansion; while materials with high thermal conductivity often have a low coefficient of thermal expansion. If transient thermal behavior in the conduction path is taken into consideration, there is a mutual constraint between thermal diffusivity, volumetric heat capacity, and the achievable upper frequency limit. Thermal shock resistance indicators reveal the contradiction even more directly: to improve the material's ability to resist cyclic thermal shock, a low elastic modulus and a low coefficient of thermal expansion are required—which is completely opposite to the high stiffness and high expansion required for work.

[0005] Within this parameter space constrained by multiple physical factors, the range of ideal materials that can be selected based solely on the single mechanism of thermal expansion is extremely narrow. Many materials that excel in certain aspects but are overlooked under traditional paradigms—such as boron fibers with extremely high axial tensile strength but a relatively low coefficient of thermal expansion, and silicon carbide and other advanced ceramics with good mechanical properties but whose bending strength in a two-dimensional configuration far exceeds their compressive strength—have long been excluded from the technological vision of thermoelectric conversion. However, thermoinduced deformation itself is not a physical effect that needs to be discarded, but rather one that needs to be redirected: by using external constraint structures to transform the thermal expansion or contraction of materials into high-intensity stresses in multiple available mechanical resistance directions, the traditional paradigm's single dependence on the coefficient of thermal expansion can be broken, allowing these materials to realize their potential advantages within a completely new mechanical framework.

[0006] Therefore, there is an urgent need in this field for a solid-state power generation unit that breaks with traditional paradigms and can make full use of the suitable mechanical resistance of each material.

[0007] It should be noted that the specific material names mentioned in the specification and claims of this invention are merely illustrative examples and do not constitute a limitation on the scope of protection of this invention. Any solid material with thermo-deformable properties and suitable for constrained stress structures can serve as the core working body of this invention; any piezoelectric medium that can convert mechanical stress into electrical energy under pure pressure conditions can serve as the piezoelectric element of this invention. Summary of the Invention

[0008] The purpose of this invention is to provide a constrained thermo-stress power generation unit that breaks the path dependence of traditional technology on three-dimensional volume expansion. This allows the working material to no longer be limited to bulk compressive strength, but to be constructed into a one-dimensional linear, two-dimensional planar, or three-dimensional volume shape according to its inherent mechanical properties. Through an external constraint structure, the thermo-induced deformation of the material in the constrained direction is converted into continuous compressive force on the piezoelectric ceramic, thereby greatly expanding the range of selectable materials and ensuring that the piezoelectric ceramic is always in a safe working condition under pure pressure.

[0009] The present invention provides a constrained thermal stress power generation unit, comprising: a core working body, an external constraint structure, and a piezoelectric ceramic array.

[0010] The core working body is made of a solid material with thermo-deformable properties. Thermo-deformable properties refer to the inherent physical property of a material to undergo dimensional changes (expansion or contraction) when temperature changes. The choice of material and spatial configuration of the core working body is unrestricted—it can be a block, sheet, fiber bundle, or other irregular structure to accommodate the mechanical properties of different materials.

[0011] An external constraint structure is provided along at least one direction of the core working body. The constraint structure has sufficient mechanical restraint in that direction to suppress thermally induced deformation of the core working body, thereby converting the deformation into mechanical stress. Depending on the configuration of the core working body, the constraint structure can be a winding layer, a rigid shell, a rigid end plate, or other equivalent limiting structure.

[0012] The piezoelectric ceramic array is positioned within the force transmission path between the core working body and the external constraint structure. When the core working body is heated, its deformation is limited by the constraint structure, and the resulting mechanical stress acts on the piezoelectric ceramic array through the force transmission path, forming a continuous compressive force that drives the piezoelectric ceramics to generate electricity.

[0013] The external constraint structure, together with the core working element, applies a basic preload to the piezoelectric ceramic array even before the core working element is heated, ensuring the array is under pure compression. The establishment of this basic preload requires the participation of the core working element—in the one-dimensional fiber scheme, the preload is directly provided by the pre-stretching of the fiber bundle, with the end plate acting as a force transmitter, converting the tension into pressure on the piezoelectric ceramic array; in the two-dimensional sheet and three-dimensional block schemes, the preload is applied by the external constraint structure, with the sheet or block acting as the load-bearing body, absorbing compressive stress and forming a force balance with the piezoelectric ceramic array. Regardless of the dimension, the purpose of the basic preload is to establish a stress baseline for the piezoelectric ceramic that is always above zero, ensuring it remains under compression throughout the entire working cycle.

[0014] Optional Feature 1: Thermal Insulation and Force Transfer Structure. A thermal insulation and force transfer structure can be set between the core working element and the piezoelectric ceramic array to block heat flow to the piezoelectric ceramic while transferring thermally induced mechanical stress. This structure can be integrally molded using a gradient porous material: the dense surface is bonded to the piezoelectric ceramic to bear and transfer stress; the porous surface is bonded to the core working element to provide a thermal resistance barrier.

[0015] Optional Feature 2: Independent Modularization. The power generation unit can be packaged into standardized independent modules, with unified heat input interfaces, heat dissipation interfaces, and electrical output interfaces, supporting parallel or series deployment of multiple modules. Core working principle

[0016] This invention breaks away from the traditional paradigm that work-performing materials must be three-dimensional blocks and utilize compressive strength, liberating work-performing materials from their dimensional constraints and opening up two entirely new dimensions of utilization: Two-dimensional planar (utilizing bending resistance): The core working body is a thin sheet with outstanding bending strength along its thickness direction. When heated, the expansion or contraction tendency of the sheet is restricted by a rigid constraint plate attached to its main surface, which is transformed into a fluctuation of compressive force on the piezoelectric ceramic array along the thickness direction; One-dimensional linear (utilizing tensile strength): The core working element is a fiber bundle, which has outstanding tensile strength along the axial direction. The two ends of the fiber bundle are fixed to two end plates, and the piezoelectric ceramic array is clamped between the two end plates. During assembly, a basic preload is applied directly by pre-stretching the fiber bundle. The end plates, acting as force transmission components, convert the axial tensile force of the fiber into uniform pressure on the piezoelectric ceramic array, placing it under pressure even in a cold state. When heated, the fiber bundle undergoes thermal deformation, and its axial dimensional change is limited by the two end plates, transforming into fluctuations in compressive pressure on the piezoelectric ceramic array.

[0017] In both paradigms, regardless of the direction of thermal deformation of the core working element (thermal expansion or thermal contraction), the external constraint serves to capture and limit this deformation, uniformly transforming it into a fluctuation of compressive force on the piezoelectric ceramic array. The basic preload is preset by the constraint structure and the core working element during assembly, setting the stress working point of the piezoelectric ceramic to ensure that it is under pressure in the cold state, and the pressure fluctuates around this point in the hot state, remaining purely under pressure throughout its entire lifespan.

[0018] The physical mechanism of prestress and stress fluctuation. The fundamental physical insight that distinguishes this invention from traditional thermal expansion power generation lies in the fact that work is the product of force and displacement. Traditional solutions pursue large deformation (large displacement), attempting to generate sufficient displacement to drive the piezoelectric element through the free thermal expansion of the material; this invention, however, pursues large stress, constraining the material on an extremely high prestress base, so that its thermally induced deformation is suppressed and transformed into high-intensity stress oscillations near the high-voltage operating point. The charge output of the piezoelectric ceramic is proportional to the rate of change of stress rather than the absolute value of stress. The role of prestress is to set a stress operating base point for the piezoelectric element that is always above zero, ensuring that it does not enter the tension zone during the entire cycle; what truly drives the piezoelectric ceramic to output electrical energy is the stress fluctuation caused by thermal deformation—the amplitude of this fluctuation depends on the material's coefficient of thermal expansion, elastic modulus, and temperature difference, and the frequency of the fluctuation depends on the speed of thermal cycling. Under this architecture, because the core working element is constrained to the direction of force suitable for its shape and mechanical properties (tensile strength of fibers along the axial direction and bending strength of sheets along the thickness direction), the prestress can be safely set to hundreds of megapascals or even gigapascals, far exceeding the equivalent stress that piezoelectric ceramics can withstand in an unprotected state. The prestress sets a safe baseline for energy conversion, and thermal stress fluctuations are superimposed on this baseline, driving the piezoelectric ceramic to continuously output electrical energy. The structural design of the piezoelectric ceramic being subjected to pure pressure throughout its lifespan ensures that this safe baseline never diminishes.

[0019] Stress adaptation mechanisms in different dimensions. The three dimensional configurations correspond to different stress transmission paths, but their common essence is to safely adapt the thermal stress generated by the core working element to the allowable compressive stress range of the piezoelectric ceramic. In the one-dimensional fiber scheme, the fiber bundle bears axial tensile stress in the thousands of gigapascals, with a total tensile force reaching tens of tons. Rigid end plates fixed at both ends distribute the concentrated load on the fiber cross-section into a uniform surface pressure on the piezoelectric ceramic surface—the area ratio of the end plates naturally constitutes a stress transformer, converting the GPa-level linear tension into a MPa-level surface pressure that the piezoelectric ceramic can withstand. In the two-dimensional sheet scheme, the thermal stress generated by the sheet already possesses surface distribution characteristics. When the stress level matches the allowable range of the piezoelectric ceramic, it can be directly transmitted through the pressure equalization plate. When the stress exceeds the limit, a gradually changing cross-sectional area frustum structure can achieve stress adaptation during the force transmission process. This frustum simultaneously performs the dual functions of heat insulation and force transmission. In the three-dimensional block design, the outer surface of the block itself forms a continuous surface, and the stress has initially formed a surface distribution pattern. As needed, local stress adjustment can be achieved by direct bonding or by adding frustums. Although the adaptation methods of the three dimensions are different, their common effect is to ensure that the piezoelectric ceramic always receives stress fluctuations from the core working body within its safe pure compressive range.

[0020] Dimensionality and Material Utilization Efficiency. In the three dimensional configurations disclosed in this invention, from three-dimensional blocks to two-dimensional sheets to one-dimensional lines, the material utilization efficiency of the core working body shows a progressively increasing trend. This trend is not due to the choice of specific materials, but rather determined by the uniformity of stress distribution in each dimension. When a three-dimensional block is under compression, the internal stress field exhibits a significant non-uniform distribution, and different parts of the material cannot simultaneously approach their allowable limits. In the bending mode, the stress on the upper and lower surfaces of the two-dimensional sheet is uniform, improving utilization efficiency. When a one-dimensional fiber is under axial tension, the stress is equal everywhere on the cross-section of the entire fiber, allowing it to simultaneously approach the material's ultimate tensile strength, and the utilization efficiency approaches an ideal state. This physical law provides a clear direction for the evolution of power density in power generation units: under the premise of meeting the operating temperature range and engineering feasibility, higher-dimensional constraint schemes should be prioritized to approach higher performance limits. Simultaneously, each of the three dimensional configurations has its irreplaceable applicable scenarios—the engineering implementation of the three-dimensional block is the simplest, the two-dimensional sheet has the best overall cost-effectiveness in the mid-temperature range, and the one-dimensional fiber represents the ultimate direction for ultimate specific power. This invention unifies the three dimensions under the same constrained force framework, allowing system designers to flexibly select the appropriate model based on specific application scenarios, with each model playing its strengths in its optimal temperature range and configuration.

[0021] The above dimensional classification is merely an exemplary classification for the convenience of describing the technical solution of the present invention. It does not exclude the core working body from adopting an irregular configuration between the dimensions, nor does it exclude the use of core working bodies of multiple dimensions in the same power generation unit.

[0022] The applicability of carbon fiber in the ultra-high temperature range. It should be noted that in the aforementioned one-dimensional fiber solutions, when carbon fiber is used as the core working element, it exhibits irreplaceable comprehensive performance advantages in the ultra-high temperature range (1500°C to 2500°C). Carbon fiber is the only engineering fiber that simultaneously possesses GPa-level tensile strength, hundreds of GPa elastic modulus, ultra-high thermal conductivity of 400–700 W / (m·K), and low density below 2.0 g / cm³. In an inert atmosphere or vacuum environment, the short-term tensile strength of carbon fiber hardly decreases above 2000°C, and its axial thermal expansion coefficient becomes positive in this temperature range, reaching approximately 1.6–2.1 × 10⁻⁻⁻⁻⁶. 6 At a temperature difference of 1000°C, the thermal stress generated can cause the theoretical specific power of its core working element to exceed 27 kW / kg. It should be noted that the coefficient of thermal expansion of carbon fiber in the ultra-high temperature region is affected by factors such as the type of precursor and the graphitization temperature, and varies between different types. However, publicly published experimental data show that in an inert atmosphere environment above 1500°C, the axial coefficient of thermal expansion of carbon fiber remains basically stable and positive, with a value of approximately 1.6 × 10⁻⁻⁻⁶. 6 / °C to 2.1×10⁻ 6 Within the range of / °C, this physical fact provides a reliable design basis for the confinement scheme of carbon fibers in the ultra-high temperature region. Future Evolution

[0023] The physical potential of the "multidimensional confined thermo-stress power generation" methodology disclosed in this invention has not yet been fully explored by currently available material data. With the continuous advancement of materials science and micro / nano manufacturing technology, the performance ceiling of the core working element is expected to achieve a further leap of orders of magnitude in the following directions.

[0024] Regarding materials, sapphire single-crystal wafers (~8.67 kW / kg), ZTA wafers (~6.91 kW / kg), boron fibers (~19.9 kW / kg), and silicon carbide fibers (~12.9 kW / kg) are all commercially available and mature materials, and their performance data constitute a solid lower limit for the power-to-weight ratio advantage of this invention. Carbon fiber systems—especially pitch-based ultra-high modulus carbon fibers represented by Mitsubishi Chemical's DIALEAD K13D2U (elastic modulus 935 GPa, tensile strength 3.8 GPa)—represent a breakthrough in the physical upper limit. In the ultra-high temperature range (above 2000°C), carbon / carbon (C / C) composites remain irreplaceable candidate materials due to their extremely high temperature resistance in inert atmospheres and their mechanical strength that does not decrease with temperature; the CTE of C / C composites can be achieved from 0 to 8.5 × 10⁻⁻⁻⁶ through methods such as radial bar weaving, modified pitch matrix, and nano-doping. 6Customization within a wide range of °C provides ample engineering flexibility for optimizing specific power under extreme temperature variations.

[0025] In the field of piezoelectric transducers, the ultimate energy density of a system is determined by the limiting performance of the piezoelectric material. The "extremely high prestress + micro-amplitude stress oscillation" working mode constructed in this invention provides near-ideal mechanical boundary conditions for special piezoelectric ceramics and piezoelectric single crystals with high piezoelectric constants, high Curie temperatures, and high mechanical quality factors. Currently, the best-performing PZT-based ceramics and relaxor ferroelectric single crystals (such as PMN-PT) in publicly available data only represent the current level of commercialization. With continued investment from materials scientists in this direction, further improvements in piezoelectric transducer efficiency will directly translate into a proportional increase in system-level specific power.

[0026] At the micro / nano manufacturing level, the micrometer-scale reduction of one-dimensional fiber filament diameter, the sub-millimeter-scale reduction of two-dimensional sheet thickness, and the maturity of three-dimensional bulk wall thickness reduction and pre-embedded high thermal conductivity contacts will jointly drive the cycle frequency to leap upward from the current 50 Hz level. Further reduction in the diameter of carbon fiber filaments can compress the heat penetration time to the microsecond level, at which point the system-level specific power is expected to achieve another order of magnitude leap from the current level.

[0027] This guiding principle of achieving generational increases in power density by continuously approaching the physical limits of materials is the fundamental direction of the long-term evolution of this invention. The aforementioned future evolution direction is a reasonable projection based on currently available material data and technological trends, and does not constitute a limitation on the scope of protection of this invention. With the development of materials science, any material and process that can satisfy the constraint-based force principle described in this invention, regardless of its specific performance parameters, falls within the scope of protection of this invention. Beneficial effects

[0028] A paradigm shift: Breaking away from the traditional reliance on three-dimensional volumetric expansion, this approach expands the available work dimension from bulk compressive strength to sheet bending strength and fiber tensile strength, thus overcoming the material selection dilemma caused by the coupling of multiple parameters such as thermal expansion coefficient, specific heat capacity, and elastic modulus in the traditional paradigm. This shift does not resolve the inherent contradictions between the aforementioned physical quantities, but rather opens up a new mechanical dimension, allowing a large number of high-performance materials previously excluded from the thermoelectric conversion field to be included in the usable range, resulting in an order-of-magnitude expansion of the material selection space.

[0029] Significantly increased power density: Under the constraint scheme of this invention, the thermal stress fluctuations generated by the core working element directly drive the piezoelectric ceramic to generate electricity, achieving extremely high theoretical specific power. Taking the fully constrained condition as an example: In the two-dimensional thin-film scheme, a sapphire single-crystal thin film is used (elastic modulus approximately 345 GPa, coefficient of thermal expansion approximately 5.0 × 10⁻⁻⁻⁴). 6With a temperature of approximately 3.98 g / cm³ and a high-temperature bending strength of 450~895 MPa, the core working element has a theoretical specific power of approximately 8.67 kW / kg under a temperature difference of 400°C and a cycling frequency of 50 Hz. It utilizes zirconia-toughened alumina (ZTA) sheets (elastic modulus approximately 350 GPa, coefficient of thermal expansion approximately 9.0 × 10⁻⁻⁻⁶). 6 (At a temperature of approximately 4.1 g / cm³, density of approximately 4.1 g / cm³, and flexural strength of 600~656 MPa), it can reach approximately 6.91 kW / kg at a temperature difference of 200°C and a Hz of 50 Hz. In the one-dimensional fiber scheme, boron fibers are used (elastic modulus approximately 400 GPa, coefficient of thermal expansion approximately 4.5 × 10⁻⁻⁻⁴). 6 With a density of approximately 2.54 g / cm³ and a tensile strength of approximately 3500 MPa, it can achieve a power output of approximately 19.9 kW / kg at a temperature difference of 500°C and a frequency of 50 Hz; it is made of silicon carbide fiber (elastic modulus of approximately 380 GPa, coefficient of thermal expansion of approximately 4.1 × 10⁻⁻⁻⁶). 6 At a temperature of approximately 3.10 g / cm³ and a tensile strength ≥2800 MPa, the power output can reach approximately 12.9 kW / kg under the same conditions. As a reference at the component level: the highest reported specific power of flexible gallium arsenide thin-film solar cells is approximately 2153 W / kg, and the specific power of flexible InGaP / GaAs tandem solar cell modules exceeds 5000 W / kg. The core working element of this invention, considering only the weight of the material itself under thermal stress, theoretically achieves a specific power several to hundreds of times greater than the aforementioned cutting-edge technologies. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the core principle of the power generation unit of the present invention (taking a thin-plate core working body as an example, it shows the force transmission path of the core working body compressing the piezoelectric ceramic after its thermal expansion is suppressed by the constraint plate). Figure 2 This is a schematic diagram of another embodiment of the power generation unit of the present invention (taking a fiber bundle-shaped core working body as an example, showing the force transmission path of the core working body squeezing the piezoelectric ceramic after being heated and contracted and restricted by the end plate). Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0032] Example 1: The core working body of the two-dimensional planar unit (utilizing bending resistance properties) is a zirconia-toughened alumina (ZTA) sheet with dimensions of 40mm × 40mm × 0.5mm. ZTA combines the high elastic modulus of alumina (approximately 350 GPa) with the phase transformation toughening mechanism of zirconia. Its bending strength along the thickness direction can reach 600-800 MPa, which is far higher than that of conventional alumina ceramics of the same thickness, and its coefficient of thermal expansion (approximately 9.0 × 10⁻⁻⁻⁶) is also high. 6 ( / °C) is significantly superior to pure alumina, and can generate high-intensity thermal stress fluctuations within a safe temperature difference of 200°C.

[0033] The external constraint structure consists of two rigid constraint plates positioned opposite each other, secured by bolts or fiber winding, applying a basic preload to the components sandwiched between them. In cross-section, from one constraint plate to the other, the components are sequentially: a first constraint plate, a piezoelectric ceramic array, a thermal insulation and force transmission structure, a ZTA sheet, and a second constraint plate. After the two constraint plates are preloaded by bolts or fiber winding, the piezoelectric ceramic array is under pure pressure in its cold state, and the ZTA sheet is also pressed between the thermal insulation and force transmission structure and the second constraint plate. The thermal insulation and force transmission structure is a gradient porous SiC plate, with its dense surface tightly attached to the piezoelectric ceramic and its porous surface tightly attached to the ZTA sheet surface. This structure transfers the stress generated by the sheet's heating to the piezoelectric ceramic while simultaneously blocking heat conduction to it.

[0034] During heating, the ZTA sheet undergoes thermal expansion along its thickness. Because the spacing between the two constraint plates is limited by bolts or a winding layer, the sheet's expansion tendency can only be translated into continuous compressive force on the thermal insulation and force-transmitting structure and the piezoelectric ceramic array. During this process, the two constraint plates provide back-to-back support for the piezoelectric ceramic, ensuring it remains under pure compressive stress while enduring varying compressive forces. Upon cooling, the sheet contracts, and the compressive stress returns to the initial pre-tightening level. Throughout the entire process, the piezoelectric ceramic remains under pure compressive stress, and the pressure it bears fluctuates synchronously with the periodic changes in the sheet's temperature, driving power generation.

[0035] Example 2: A one-dimensional linear unit (utilizing tensile properties) uses a carbon fiber bundle as its core working element, composed of thousands of carbon fiber filaments. The tensile strength of carbon fiber can reach several gigapascals, its elastic modulus can reach several hundred gigapascals, and its density is less than 2.0 g / cm³. Because the cross-section of a single carbon fiber is extremely small, thousands of filaments are needed to form a bundle to provide sufficient resultant force. To ensure mechanical stability, multiple carbon fiber bundles are arranged at multiple points between the end plates, with each bundle evenly distributed circumferentially along the end plates to avoid eccentric loading.

[0036] The external constraint structure includes a first end plate and a second end plate, both of which are high-rigidity, lightweight plates. The two ends of the carbon fiber bundle are wound and fixed to the two end plates, respectively. During assembly, the pre-stretched carbon fiber bundle is subjected to high tensile stress, while simultaneously applying a basic preload force to the piezoelectric ceramic array clamped between the two end plates via the end plates, placing it in a purely compressive state even when cold. Here, the carbon fiber bundle serves both as the core workpiece generating thermal stress and as an elastic element applying the basic preload force, resulting in an extremely simple structure.

[0037] During heating, the carbon fibers undergo thermal deformation, and this dimensional change is restricted by the end plates. The tensile stress within the fibers fluctuates accordingly, and after being transmitted through the end plates, it is converted into fluctuations in compressive pressure on the piezoelectric ceramic array, driving power generation. After cooling, the compressive pressure returns to the pre-tightened level. Throughout the entire process, the piezoelectric ceramics are always under pure compressive stress.

[0038] Example 3: Utilizing compressive strength (a variation of a traditional three-dimensional block), the core working body is a hollow cubic C / C composite shell, pre-tightened externally by a carbon fiber winding layer. The shell has a six-sided closed cubic configuration, with each outer surface serving as a force-bearing surface. Piezoelectric ceramic arrays are positioned along six force transmission paths between each surface of the shell and the winding layer, achieving multi-faceted synchronous force generation. Each surface has a central circular hole, which serves to reduce the force-bearing area, thereby decreasing outward compressive force and alleviating the stress burden on the force-transmitting cone; it also facilitates the assembly of internal wiring. The winding layer acts as the external constraint structure; during heating, the shell expands outward but is restrained by the winding layer, and this expansion tendency translates into continuous compressive force on the piezoelectric ceramic array. This is a compatible implementation of the traditional volume expansion paradigm within the framework of this invention, demonstrating that the scope of protection of this invention does not exclude any feasible dimensional choices.

Claims

1. A constrained thermal stress power generation unit, characterized in that, include: The core working body is made of a solid material with thermo-deformable properties; An external constraint structure is provided along at least one direction of the core working body. The constraint structure limits the core working body in its provided direction, so that the thermal deformation generated by the core working body in that direction is suppressed and converted into mechanical stress. A piezoelectric ceramic array is arranged in the force transmission path to withstand the mechanical stress generated by the interaction between the core working body and the external constraint structure. The core working body and the external constraint structure together apply a basic preload to the piezoelectric ceramic array, so that the piezoelectric ceramic array is in a pure compressive state. During the cycle of heating and cooling of the core working body, its deformation is restricted by the constraint structure, so that the compressive force acting on the piezoelectric ceramic array changes periodically. During the change, the piezoelectric ceramic array is always in a pure compressive state to drive its power generation.

2. The power generation unit according to claim 1, characterized in that, The material selection and spatial configuration of the core working body are unrestricted, including blocks, sheets, fiber bundles, or combinations thereof, to adapt to the mechanical properties of different materials.

3. The power generation unit according to claim 1, characterized in that, The core working body is a thin sheet with outstanding bending strength along its thickness direction; the external constraint structure is a rigid constraint plate attached to the main surface of the core working body; when the core working body is heated, the deformation along its thickness direction is suppressed by the constraint plate and converted into extrusion force on the piezoelectric ceramic array.

4. The power generation unit according to claim 1, characterized in that, The core working body is linear or rod-shaped, with outstanding tensile or compressive strength along the axial direction; the external constraint structure is a non-stretchable or non-compressible limiting member set along the axial direction; when the core working body is heated, the axial deformation is suppressed by the limiting member and converted into axial compressive force on the piezoelectric ceramic array.

5. The power generation unit according to claim 1, characterized in that, A heat-insulating force-transmitting structure is set between the core working body and the piezoelectric ceramic array to block the conduction of heat to the piezoelectric ceramic while transmitting thermally induced mechanical stress.

6. The power generation unit according to claim 5, characterized in that, The heat-insulating force-transmitting structure is integrally formed from a gradient porous material, with its dense surface bonded to a piezoelectric ceramic array and its porous surface bonded to a core working body.

7. The power generation unit according to any one of claims 1 to 6, characterized in that, The external constraint structure provides basic preload through fiber winding, bolt fastening, or shell encapsulation.

8. The power generation unit according to any one of claims 1 to 6, characterized in that, The power generation unit is packaged as a standardized independent module, with a unified heat input interface, heat dissipation interface and electrical output interface.

9. A constrained thermal stress power generation system, comprising a plurality of power generation units as described in any one of claims 1 to 8, wherein the plurality of power generation units share a heat source and a cold source in parallel, or are thermally coupled in series with the heat dissipation interface of the previous unit to the heat input interface of the next unit, thereby realizing the cascade utilization of thermal energy.

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