MECH 321 LAB 3 Experiment Fracture Toughness Testing of Aluminum Alloys (Properties & Failure of Materials) 2026 Concordia University

MECH 321 LAB 3 Experiment Fracture Toughness Testing of
Aluminum Alloys (Properties & Failure of Materials) 2026
Concordia University
Experiment 3
Fracture Toughness Testing of Aluminum Alloys




MECH 321 Lab Section MI - X
Group A
Winter 2025




Prof. Sam Eskadarian



Concordia University
Montreal, QC, Canada




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,TABLE OF CONTENTS

TABLE OF CONTENTS ............................................................................... 2
LIST OF TABLES AND GRAPHS ..................................................................... 2
OBJECTIVE .......................................................................................... 3
INTRODUCTION ..................................................................................... 3
EQUIPMENT.......................................................................................... 6
PROCEDURE ......................................................................................... 7
RESULTS ............................................................................................. 9
Table xx: Load at fracture tabulated calculations [1]........................................ 14
SAMPLE CALCULATIONS ....................................................................... 19
DISCUSSION........................................................................................ 19
CONCLUSION ...................................................................................... 21
REFERENCES....................................................................................... 21


LIST OF TABLES AND GRAPHS
Figure 1: Stress in material of infinite extent
Figure 2: Stress in a non-idealized situation
Figure 3: Types of load displacement behaviour, Type I – tearing, Type II – mixed, Type III -
cleavage
Figure 4: Instron Tensile Machine – Model 3382
Table 1: Lab experiment specimens' measurements and data [1]
Figure 5: Sketches of experimental specimens’ breaks [1]
Figure 6: Load vs displacement from the 1in specimen data
Figure 7: Load vs displacement from the 1.5in specimen data
Figure 8: Load vs displacement from the 1.5in fatigued specimen data
Figure 9: Load vs displacement from the 2in fatigued specimen data
Figure 10: 1in specimen post fracture
Table 2: Load at fracture tabulated calculations [1]
Table 3: Stress intensity at fracture tabulated calculations [1]
Table 4: KIC validity tabulated calculations [1]
Figure 11: 1.5in specimen post fracture
Figure 12: 1.5in fatigued specimen post fracture

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, Figure 13: 2in fatigued specimen post fracture


OBJECTIVE
The objective of this lab is to determine how a crack in a material can affect its strength. This is a
property of material called Fracture Toughness, and it will be determined for Aluminum in this
experiment.


INTRODUCTION
The presence of a crack in a material is to be closely followed as it represents a concentration of
stress. These cracks can arise from fatigue or material defects and are unavoidable. In industries
such as aviation or maritime, engineers monitor closely these cracks to ensure they can remain
operable under safety norms.
To understand the stress around a crack some assumptions can be made to simplify the analysis.
We can consider a uniform material assumed to be of infinite extent and having a semi-infinite
horizontal in the negative x-direction as depicted in figure 1. If a stress is applied in the y-direction,
the stress far away from the crack will be uniformed and the stress concentration near the crack
can be calculated as such:
𝐾
𝜎𝑦 =
√2𝜋𝑥
The stress intensity, K controls the overall magnitude of the stress field.




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