Strain Rosette Layout for In-Situ Plastic Deformation Detection
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Solution Overview
Problem
Existing methods fail to detect plastic deformation of materials without knowledge of the material's stress state, geometric dimensions, and mechanical characteristics.
Innovation Solution
A method and detector using at least four strain sensors forming two rosettes turned at an angle and offset by a vector, allowing independent strain and stress measurements to determine the moment of plastic deformation by monitoring strain increments and stress proportionality loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional strain measurement methods (rosettes with dial extensometers or single rosette configurations) are used, then stress state measurement is possible within limited ranges (0.6-0.9 of limit of proportionality), but detection of plastic deformation moment cannot be achieved without knowledge of material characteristics and initial stress state
Solution Approach 1:
The measurement system is segmented into multiple independent strain sensor rosettes (at least two) positioned at different locations and orientations on the material surface. Each rosette independently measures strain in its local coordinate system, and the combined data from multiple segmented measurement points enables detection of plastic deformation moment without requiring knowledge of initial stress state or material characteristics.
Solution Approach 2:
The solution transitions from single-plane strain measurement to multi-dimensional strain measurement by placing rosettes at different orientations and positions. This dimensional expansion in measurement space allows the system to detect the moment of plastic deformation through comparative analysis of strain increments across multiple dimensions, eliminating the need for prior knowledge of material properties.
2Reliability
If multiple strain sensors are used to form rosettes for stress measurement, then measurement coverage is improved, but the ability to detect plastic deformation without material property knowledge is lost
Solution Approach 1:
The multi-rosette measurement system serves multiple functions: it measures stress state in the elastic range, detects the moment of plastic deformation onset, and operates without requiring prior knowledge of material characteristics or initial stress conditions. This universal applicability is achieved by analyzing strain increments and their proportionality relationships across multiple rosette configurations.
Solution Approach 2:
The system monitors changes in strain parameters over time and detects plastic deformation through the loss of proportionality in strain increments between different rosette measurements. By focusing on parameter relationships (proportionality) rather than absolute values, the system adapts to unknown material states while maintaining measurement reliability.
3Device complexity
If conventional single rosette measurement is used, then device simplicity is maintained, but detection of plastic deformation moment without material property knowledge is not possible
Solution Approach 1:
Multiple strain sensor rosettes are merged into a single integrated measurement system where the combined data from all rosettes is analyzed together. This merging approach preserves relative simplicity while enabling detection of plastic deformation moment through the comparative analysis of strain increments and proportionality relationships across the merged dataset.
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
Unambiguously identifies the moment of plastic deformation in materials, regardless of initial stress state or mechanical properties, enabling early detection of yield point for structural health monitoring.
Implementation Method 1
strain sensors for measuring strain in the material
Data Source
AI summary
Method for identifying a plastic deformation of material of an object in situ using strain sensors operating on the principle of electrical resistive strain gauging, fibre optic measurements using fibre Bragg gratings (FBG), vibrating wire sensors ( )VW, distributed fibre optic sensors (DFOS), inductive, capacitive, or piezoresistive sensors, in which in the monitored area (W) subjected to any load condition, there are placed at least four strain sensors (εs) constituting at least two rosettes (I), (II) turned with respect to each other by any angle (α) other than zero and freely shifted with respect to each other by a vector (V) for measuring any plane strain condition, the rotation angle and the displacement of the rosettes (I), (II) are chosen so that no more than two sensors (εs) between the rosettes are parallel to each other or lie on the same straight line, at least two principal strain states (ε1, ε2) and principal stresses (σ1, σ2) respectively are determined for the monitored area (A), and by monitoring the object, increments of principal strains (Δε1), (Δε2) and/or increments of principal stresses (Δσï), (Δσ2) are calculated, in successive moments of time, for each separated rosette, which below the yield point of the monitored area are proportional between the rosettes, on this basis, the plastic deformation of material indices are determined, and by monitoring the area the yield point is detected at the moment of disappearance of the proportionality of the increments, i.e. a sudden change in the value of the determined yield indices normal to the state below the yield point of a given area.