Pratique du Shadowing: Material Properties 101 - Apprendre l'anglais à l'oral avec la vidéo
Création de la leçon...
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This video is going to be a bit different to my usual videos, but I want to talk about material properties and the words we use to describe them.
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This is information you are going to need to fully understand future videos.
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By the end of this video, I want you to understand 6 keywords that we use to describe materials.
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These are stiff, strong, ductile, brittle, tough and hard.
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With these words, you will be able to describe pretty much any material
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and better understand why certain materials are used in different applications.
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More technical videos like this will be uploaded to my second channel from now on, which you can subscribe to by following this link.
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I'll try and back up the technical stuff with interesting real-world examples.
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First we are going to learn what a tensile test is.
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A tensile test is a fundamental test in material mechanics.
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It's performed by pulling a sample of material apart until failure, while measuring the force and displacement.
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It provides us with something called a stress strain curve, which tells us a lot about the material's reactions to forces.
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In this scenario, the stress is defined by the force applied to the test sample, divided by the cross-sectional area.
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This gives us units of newtons per meter squared, which you may recognize as the metric unit for pressure, Pascals.
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Stress goes on the y-axis.
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Strain describes how much deformation has occurred with that applied force, and it is found by dividing the change in length by the original length.
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This is placed on the x-axis.
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Let's watch this test again and see what information we can get from the stress strain graph.
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As the stress rises, the material begins to deform.
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This initial linear region is elastic deformation, That means if we remove the force, the material will regain its original shape.
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Think of how a rubber band can deform hugely and still come back to its original shape.
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The end of this linear elastic deformation is marked by the yield point.
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From here out, any additional stress will cause permanent deformation.
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This is called plastic deformation.
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The stress continues to rise until it hits the ultimate tensile strength point.
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This is the ultimate strength of the material, the most stress it can handle.
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From here, less stress is needed as the material begins to decrease in cross section, which you can see happening here.
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This is called necking.
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This continues until the material fractures.
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We can get a lot of really useful information from this graph.
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The first is Young's modulus, otherwise known as the elastic modulus.
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This describes how stiff the material is, and it is obtained by finding the slope of this linear region.
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A steeper slope means a stiffer material.
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For example, a high carbon steel may look like this, whereas a flexible material with the low Young's modulus, like rubber, would look like this.
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This graph is not to scale, but it should give you an idea of how this information is represented.
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Young's modulus is one of the most used properties in engineering, as we can use it to predict deflection in a huge range of scenarios.
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Yield strength and ultimate tensile strength are two other important properties.
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An engineer will divide the yield or ultimate strength by the safety factor to achieve the max allowable stress, which is used to influence the design of the product.
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Usually engineers will aim to keep the max possible stress well below failure, but safety factors differ between industries.
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So we've seen a stiff material and a flexible material.
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Now let's look at a material in between.
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This material can be described as tuff and ductile.
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Tuff simply means the material can absorb a lot of energy without breaking.
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The area under the graph here defines how much energy is absorbed.
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Ductile means it deforms under pressure.
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The two previous materials could also be considered ductile.
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Springsteel is a tough and ductile material with a high yield strength which is why it is used in springs.
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Springs need to absorb energy without permanently deforming.
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The opposite of ductile is brittle.
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A brittle material is a material that breaks with very little deformation.
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Glass, ceramics and cast iron all fall into this category.
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You can actually tell if a material is brittle or ductile by examining the fracture surface after they have broken.
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A ductile material will have this characteristic cup and cone fracture surface, whereas brittle fractures have granular flat looking fracture surfaces.
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Some materials can go from ductile to brittle when their temperatures are lowered.
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This was actually a massive problem during World War 2 with the Liberty ship.
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Several Several of these ships literally broke in half with no warning, including the SS John P.
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Gaines, which broke in half in the frigid waters of the Bering Sea.
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It was later discovered that the grade of steel being used became brittle at lower temperatures.
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This problem was made worse by the stress concentration at the hatches, which you learned about in my first video, Why are plane windows round?
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This embrittlement is also thought to have contributed to the fracture of the titanic's hull.
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The final material property I want to talk about is hardness.
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It is directly related to the stiffness and yield strength of the material, but it is used to describe how difficult it is to dent, scratch and abrade materials.
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One way this material property is measured is with the Rockwell hardness test.
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This test involves three steps.
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First a minor load is applied to the material by an indenter.
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This establishes a zero point.
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For the second step, a major load is then added, which indents the material.
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And for the final step, the major load is removed, while maintaining the initial load.
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The difference in depth between the first and third step is then used to calculate the hardness of the material.
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Diamond is a very hard material, which is why it is used in cutting tools.
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One of the fantastic properties of steel is its ability to be heat treated, to have its hardness tailored in different areas.
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For example, with swords you want your cutting edge to be hard but the core of the blade to be ductile.
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This means the sword can bend under pressure without breaking, while the cutting edge can resist damage.
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As always, thanks for watching.
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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale de niveau C1 s’appuie sur la vidéo « Material Properties 101 ». Les mots qui reviennent le plus souvent : material, stress, ductile, brittle, strength. Cette vidéo contient 85 phrases et 1264 mots à répéter en shadowing. La partie parlée dure 6:06. Le locuteur parle vite, environ 207 mots par minute : attendez-vous à des liaisons et à des sons réduits. 82 % des mots font partie des 3 000 mots les plus courants en anglais ; le reste mérite d’être vu avant de commencer.
Vocabulaire clé de cette vidéo
Les 15 mots les plus avancés de la vidéo, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| distress nom | /dɪˈstɹɛs/ | détresse |
| ductile adjectif | /ˈdʌk.təl/ | ductile |
| brittle adjectif | /ˈbɹɪtəl/ | fragile |
| deformation nom | /ˌdɛfəˈmeɪʃən/ | déformation |
| fracture nom | /ˈfɹæk.t͡ʃʰəː/ | fracture |
| deform verbe | /dəˈfɔɹm/ | déformer |
| hardness nom | /ˈhɑɹdnəs/ | dureté |
| modulus nom | /ˈmɑdʒələs/ | module |
| stiff adjectif | /stɪf/ | rigide, raide |
| graph nom | /ɡɹæf/ | graphique |
| elastic adjectif | /ə-/ | élastique |
| absorb verbe | /æbˈsɔɹb/ | absorber |
| tuff nom | /tʌf/ | tuf volcanique, tuf |
| slope nom | /sloʊp/ | pente |
| axis nom | /ˈæksɪs/ | axe |
Les verbes à particule que vous entendrez
| Mot | Sens |
|---|---|
| back up verbe | reculer |
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | will be uploaded · is defined · is found |
| Present perfect have/has + participe passé — une action passée qui compte encore maintenant | has occurred · we've seen · have broken |
| Propositions relatives who / which + proposition — une précision sur une personne ou une chose | stress, which is · strength which is · material, which is |
Prononciation à surveiller
Le locuteur utilise 3 contractions et formes réduites, comme I'll, we've, wouldn't. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « sh » et « zh »: deformation /ˌdɛfəˈmeɪʃən/, deflection /dəˈflɛkʃən/, sectional /ˈsɛkʃənəl/, consultation /ˌkɑnsəlˈteɪʃən/
- Mots longs — placez bien l’accent: deformation /ˌdɛfəˈmeɪʃən/, allowable /əˈlaʊ.əbəl/, personalize /ˈpɜː.sə.nə.laɪz/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/, consultation /ˌkɑnsəlˈteɪʃən/
Les sons difficiles pour les francophones :
- /h/ — il se souffle, il n’est pas muet: hardness /ˈhɑɹdnəs/, hugely /ˈhjuːd͡ʒli/, hatch /hæt͡ʃ/, hull /hʌl/
- /tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: fracture /ˈfɹæk.t͡ʃʰəː/, modulus /ˈmɑdʒələs/, frigid /ˈfɹɪd͡ʒɪd/, hugely /ˈhjuːd͡ʒli/, hatch /hæt͡ʃ/
- /r/ anglais — langue recourbée, sans frotter la gorge: distress /dɪˈstɹɛs/, brittle /ˈbɹɪtəl/, fracture /ˈfɹæk.t͡ʃʰəː/, deform /dəˈfɔɹm/, hardness /ˈhɑɹdnəs/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme distress, ductile, brittle.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.