Dynamic photoelasticimeter with rotating birefringent element

• US 4,179,217 A
• Filed: 02/14/1978
• Issued: 12/18/1979
• Est. Priority Date: 02/21/1977
• Status: Expired due to Term

• Current Assignee: ETAT Francais As Represented By The Delegue General Pour L'Armement
• Original Assignee: ETAT Francais As Represented By The Delegue General Pour L'Armement
• Inventors: Robert, Andre J., Filippini, Jean C., Ferre, Michel
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Rosenberger, R. A.
• Application Number:
  US05/877,758
• Time in Patent Office: 672 Days
• Field of Search: 356/33, 356/34, 356/114, 356/115, 356/116, 356/117, 356/364, 356/365, 356/366, 356/367, 356/368
• US Class Current: 356/33
• CPC Class Codes: G01L 1/241 by photoelastic stress analysis
• CPC Class Codes: G01N 21/23 Bi-refringence

Abstract

This invention relates to a dynamic photoelasticimeter with a rotating birefringent element. It comprises a laser, a birefringent plate rotatable at a constant speed, a model to be studied, a circular analyzer and a photodetector supplying signals at its output having frequency components of 2ω and 4ω. The ratio of the amplitudes of these signals supplies an indication of the phase shift φ (t) contributed by the model, and the phase of the signal of the frequency 4ω contributes information as to the orientation θ of the axes of the model at the point in question.

The present invention provides a particularly simple and accurate dynamic photoelasticimeter.

Claims

1. A dynamic photoelasticimeter for measuring as a function of time the birefringent parameters θ

(t) and θ

(t) of a model at a point subjected to stresses comprising, in succession

a birefringent plate rotatable at a constant angular speed;

a circular analyzer, said model being interposed between said birefringent plate and said circular analyzer;

a photoelectric receiver;

means for detecting the output signals from said photoelectric receiver at frequencies of 2ω and

4ω

;

means for determining the ratio of the amplitudes of said 2ω and

4ω

output signals; and

means for detecting the phase of said 4ω

signal with respect to a reference frequency.

2. A dynamic photoelasticimeter for measuring as a function of time the birefringent parameters θ

(t) and φ

(t) of a model at a point subjected to stresses comprising, in succession

a source of light emitting a light wave having at least two wavelengths λ

₁ and λ

₂ ;

a birefringent rotatable at constant speed;

said model;

means for sending a first part of the light emerging from said model towards a first circular analyzer and a first photodetector, said first photodetector supplying a signal corresponding to the optical signals of wavelength λ

₁ ;

means for supplying another part of the light emerging from said model towards a second circular analyzer and a second photodetector, said second photodetector supplying a signal corresponding to the optical signals of wavelength λ

₂ ;

means for filtering the 2ω and

4ω

signals at the outputs of said first and second photodetectors;

means for measuring the output signal having a frequency of 2ω

by synchronous detection means; and

means for detecting the phase and amplitude of the 4ω

signal.

4. A dynamic photoelasticimeter according to claim 2, wherein the means for separating the optical beam into a first part and a second part is an afocal optical system.

3. A dynamic photoelasticimeter for measuring as a function of time the birefringent parameters θ

(t) and φ

(t) of a model at a point subjected to stresses comprising, in succession

a source of light emitting a light wave having at least two wavelengths λ

₁ and λ

₂ ;

a birefringent rotatable at constant speed;

said model;

means for sending a first part of the light emerging from said model towards a first circular analyzer and a first photodetector, said first photodetector supplying a signal corresponding to the optical signals of wavelength λ

₁ ;

means for supplying another part of the light emerging from said model towards a second circular analyzer and a second photodetector, said second photodetector supplying a signal corresponding to the optical signals of wavelength λ

₂ ;

means for filtering the 2ω and

4ω

signals at the outputs of said first and second photodetectors;

means for measuring the output signal having a frequency of 2ω

by synchronous detection means; and

means for measuring the output signal having a frequency of 4ω

by synchronous detection means.

5. A dynamic photoelasticimeter according to claim 3, where the means for separating the optical beam into a first part and a second part is an afocal optical system.