Hybrid Dimple-and-Void Auxetic Structures for Gas Turbine Stress Reduction

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Solution Overview

Problem

The fabrication of auxetic materials with intricate geometries within a host matrix is challenging, limiting their practical development and application, particularly in achieving negative Poisson's Ratio (NPR) behavior, which is essential for stress reduction in high-temperature environments like gas turbines.

Innovation Solution

Hybrid dimple-and-void auxetic structures with engineered patterns, comprising carefully designed voids and protrusions, are fabricated to reduce stress under displacement loading conditions, achieving customized NPR behavior and specific porosity values, which are lower than those achieved by void-only structures, while maintaining stress reduction and cooling performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If auxetic materials with intricate geometries are fabricated within a host matrix, then negative Poisson's Ratio behavior is achieved, but manufacturing complexity and difficulty increase significantly

Engineering Contradiction:

ImproveNPR behaviorVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The structure is divided into repeating unit cells, each containing a specific arrangement of voids and protrusions. This segmentation allows the complex auxetic behavior to be achieved through simple, repeatable geometric patterns that are easier to manufacture than monolithic intricate geometries.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces protrusions with specific geometric characteristics (shape, size, orientation) at local positions within the unit cell structure. These localized geometric features are engineered to trigger the desired NPR behavior under compression, allowing control of the auxetic effect without requiring complex global geometry.

Inventive Principle:

Principle #3Local quality

2Stress or pressure

If void-only structures are used to achieve NPR behavior, then stress reduction is obtained, but porosity values are higher than desired for gas turbine applications

Engineering Contradiction:

Improvestress reductionVSAvoidporosity

Core Design Contradiction:

Stress or pressureVSQuantity of substance

Solution Approach 1:

The patent combines two different structural features—voids and protrusions—within the same unit cell to create a composite auxetic structure. This composite approach allows the structure to achieve stress reduction through NPR behavior while maintaining lower porosity than void-only structures, as the protrusions provide mechanical functionality without requiring additional void space.

Inventive Principle:

Principle #40Composite materials

3Temperature

If conventional cooling holes are used in gas turbine combustors, then cooling performance is achieved, but stress levels around the holes remain high

Engineering Contradiction:

Improvecooling performanceVSAvoidstress levels

Core Design Contradiction:

TemperatureVSStress or pressure

Solution Approach 1:

Instead of using simple circular cooling holes that create stress concentrations, the patent inverts the conventional approach by using protrusions (raised features) rather than just voids. This inversion of the geometric concept allows the structure to reduce stress through NPR behavior while still providing cooling pathways, fundamentally changing how cooling holes are conceived in the design.

Inventive Principle:

Principle #13The other way round (Inversion)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The hybrid structures exhibit significant stress reduction and increased fatigue life in gas turbine components, reducing thermo-mechanical stress by up to five-fold and extending component life, while maintaining cooling performance and achieving porosity targets critical for turbine emission goals.

Implementation Method 1

The apertures are cooperatively configured with the plurality of protrusions to provide a predefined porosity while exhibiting stress reduction through negative Poisson's Ratio (NPR) behavior under macroscopic planar loading conditions

Methodology Applied

Scientific EffectNegative Poisson's Ratio (NPR) behavior: Poisson's Effect

Implementation Method 2

a sheet of rigid but elastic material is fabricated with carefully designed voids

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 3

Stress reduction is achieved, for example, through cell rotation and as a result, gives the sheet NPR behavior

Methodology Applied

Scientific EffectCell rotation:

Data Source

PatentUS10603866B2Hybrid dimple-and-void auxetic structures with engineered patterns for customized NPR behavior

Publication Date: 2020.03.31 SIEMENS CANADA LTD

AI summary

Auxetic structures, low porosity auxetic sheets, systems and devices with auxetic structures, and methods of using and methods of making auxetic structures are disclosed. An auxetic structure is disclosed which includes an elastically rigid body with a plurality of apertures extending through the elastically rigid body and a plurality of protrusions projecting from the elastically rigid body. The apertures and protrusions are arranged in an engineered pattern, such as an array of rows and columns. The apertures are cooperatively configured with the protrusions to provide a predefined porosity while exhibiting stress reduction through negative Poisson's Ratio (NPR) behavior under macroscopic planar loading conditions. In some embodiments, the protrusions, which are elliptical or semispherical dimples, are interposed in square or hexagonal patterns with the apertures, which are S-shaped through slots or circular boreholes.