Stress measurement - SINTEC-inc

Portable, semi-automatic device for non-destructive ultrasonic measurement of residual stresses

Fatigue improvement-equipment for Ultrasonic Measurements of Applied and Residual Stress (UltraMARSTM)

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1. Introduction

The portable, semi-automatic device for Ultrasonic Measurements of Applied and Residual Stress (UltraMARSTM) is designed for measurement of averaged through-thickness and surface residual and applied stresses in samples, parts, welded elements and structures non-destructively.

UltraMARS™ device is used to provide the following measurements:

and sign of uni- and biaxial applied and residual stresses in samples and real structural elements.
Uniaxial stresses and forces in pins and bolts.
Parameters of the acoustic-elastic characteristics of materials.
Residual stress change as a result of post-welding treatment and service loading.
The thickness of parts and structural elements.
Young Modulus and Poisson Ratio.

The main technical characteristics of the UltraMARS™ device:

Stress can be measured in materials with thickness 2 – 150 mm.
Error of stress determination (from external load): 5 – 10 MPa.
Error of residual stress determination: 0.1 σy (yield strength) MPa.
Stress and force measurement in fasteners (pins) 25-1000 mm long.
Option of using with independent power supply (accumulator battery 12 V).
Overall dimensions of the measurement device: 330x215x165 mm.
Weight of the measurement unit with transducers: 7.7 kg.

The supporting software allows controlling the measurement process, storing the measured and other data and calculating and plotting the distribution of residual stresses. The software also allows an easy connection with standard PC’s.

UltraMARS™ device could be used to determine the stresses in parts and structural elements during manufacturing, assembly and in service.

2. Principles of Ultrasonic Measurement of Residual Stresses

The principle of ultrasonic measurement of mechanical stresses is based on the acoustic-elastic effect. According to this phenomenon, the velocity of propagation of ultrasonic waves in solids is dependent on mechanical stresses. When material properties are known, the stress measurement could be done by determination of the velocities of propagation of longitudinal and shear polarized (in orthogonal direction) ultrasonic waves.

Properties of material are reflected in proportionality coefficients that are defined by elasticity constants of the second and third orders. These coefficients can be calculated or determined experimentally by uni- or biaxial loading (in compression or in tension) of a sample of the material.

Measurement of the propagation velocity of the elastic waves is done though the measurement of the frequency of recirculation of ultrasonic signals in the material.
Sending and receiving of the ultrasonic waves in the material are performed by piezo-electric ultrasonic transducers of longitudinal (transducer XF1) and shear (transducer YF23) waves. The transducers are installed and fixed at a point of stress measurement on the sample, part or structural element using a fixator. The fixator could be attached to the sample/part by a clamping strap, magnet or an electromagnet.
Results of stress measurement in each point on the sample are recorded and stored in the memory of UltraMARStm device microprocessor. These data are used for the calculation and drawing of distribution of residual/applied stresses.

Principles of Ultrasonic Measurement of Residual Stresses

Change of ultrasonic longitudinal wave velocity (C L) and shear waves velocities of orthogonal polarization (C SX3; C SX2) depending on the mechanical stress σ in steel A (1), steel B (2) and aluminium alloy (3): ● – C SX3; ○ – C SX2; x – C L

ultrasonic transducers Fatigue improvement-equipment for Ultrasonic Measurements of Applied and Residual Stress (UltraMARSTM)

The ultrasonic transducer/receiver for bulk ultrasonic waves

schematic view of ultrasonic through-thickness - Fatigue improvement equipment

UltraMARS™ device provides the following operations:

Control of the longitudinal, XF1 and shear, YF23 wave transducers.
Reading and analysis of controlled physical parameters of the sample/part.
Analysis of operator’s actions and providing of the recommendations on the operator’s action.
Control of the technical condition of the device.

Ultrasonic gauge for measurement of residual or applied stresses

In the proposed technique, the velocities of longitudinal ultrasonic wave and shear waves of orthogonal polarization are measured at a considered point to determine the biaxial residual stresses. The bulk waves in this approach are used to determine the stresses averaged over the thickness of the investigated elements. Surface waves are used to determine the uni- and biaxial stresses at the surface of the material. The mechanical properties of the material are represented by the proportionality coefficients, which can be calculated or determined experimentally under an external loading of a sample of considered material.

Supporting software for measurement of residual stresses in materials, parts and welded elements was developed. The developed software can control the measurement process, store the ultrasonic measurement data, calculate the residual stresses and allows using the developed technique and instrumentation with standard PC. The developed software and advanced ultrasonic gauges were integrated with the existing measurement module UltraMARS™

The Ultrasonic Computerized Complex UltraMARS-7
for measurement of residual and applied stresses

3. Technical Characteristics

№

Technical parameters

Measurement Unit

Value

1

Time of stress measurement in one point

Averaged through-thickness
Surface/subsurface

minute

~ 1

2

Maximum data recorded:

Sets of acoustic-elastic coefficients
Sets of names/numbers of measurement
Sets of frequencies and stresses

set

100

200

3

Power Requirements:

Voltage
Frequency
Consumed Power

–

VAC

Hz

W

–

110/230±10%

50/60-400

20

4

Physical Dimensions:

UltraMARS™ device
PV-UZK unit with fixator
High –frequency Connection Cable
Transducer (bulk waves)
Transducer (surface waves)

–

mm

m

mm

–

330x215x165

180x65x36

5.0

85x50x35

45x45x20

5

Weight of the UltraMARS™ device:

Measurement unit
PV-UZK unit with fixator
High –frequency Connection Cable
Set of transducers (XF1 and YF23)
Transducer (surface waves)
A transducer for surface waves

–

kg

–

7.70

6.50

0.44

0.41

0.35

0.15

6

Environmental Requirements:

Permissible operating temperature range
Permissible maximum humidity of environment
(at 35 ± 3 °C)

–

°C

%

–

0 ÷ 50

95 ± 3

4. Example of Application

manufactures and provides equipment for ultrasonic impact treatmen

Measurement of residual stresses using developed ultrasonic gauges and the universal measurement unit UltraMARS^TM in welded panel in as-welded condition and during the fatigue loading of the panel

Measurement of residual stresses using developed ultrasonic gauges and the universal measurement unit UltraMARS™ in welded panel in as-welded condition and during the fatigue loading of the panel

Distribution of residual stresses (RS) near the end of welded attachment in as welded condition:
σ33 – component of RS that is parallel to the direction of fatigue loading,
σ22 – component of RS that is perpendicular to the direction of fatigue loading