跟读练习: Material Properties 101 - 通过视频学习英语口语
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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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本课的词汇与口语要点
这节 C1 级别的口语课以视频“Material Properties 101”为素材。 视频中反复出现的词有：material, stress, ductile, brittle, strength。 这段视频共有 85 个句子、1264 个单词可供跟读。 讲话部分时长为 6:06。 说话人语速较快，每分钟约 207 个词，会出现较多连读和弱读。 82% 的单词属于英语最常用的 3,000 词，其余的词建议在练习前先学一下。
视频中的重点词汇
视频中最难的 15 个单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| brittle 形容词 | /ˈbɹɪtəl/ | 易碎的, 易损坏的 |
| deformation 名词 | /ˌdɛfəˈmeɪʃən/ | 變形 /变形, 形變 /形变 |
| fracture 名词 | /ˈfɹæk.t͡ʃʰəː/ | 骨折 |
| modulus 名词 | /ˈmɑdʒələs/ | 系数 |
| stiff 形容词 | /stɪf/ | 硬, 僵硬 |
| graph 名词 | /ɡɹæf/ | 圖表 /图表 |
| elastic 形容词 | /ə-/ | 彈性的 /弹性的, 有彈力的 /有弹力的 |
| absorb 动词 | /æbˈsɔɹb/ | 吸收 |
| tuff 名词 | /tʌf/ | 凝灰岩 |
| slope 名词 | /sloʊp/ | 斜坡, 坡 |
| axis 名词 | /ˈæksɪs/ | 軸 /轴, 軸心 /轴心 |
| aspire 动词 | /əˈspaɪɚ/ | 熱望 /热望, 渴望 |
| keyword 名词 | /ˈkiː.wɜːd/ | 關鍵詞 /关键词, 關鍵字 /关键字 |
| personalize 动词 | /ˈpɜː.sə.nə.laɪz/ | 個性化 /个性化 |
| tailor 名词 | /ˈteɪlɚ/ | 裁縫 /裁缝, 裁縫師傅 /裁缝师傅 |
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | will be uploaded · is defined · is found |
| 现在完成时 have/has + 过去分词 — 过去发生但与现在仍有关联的事 | has occurred · we've seen · have broken |
| 定语从句 who / which + 从句 — 补充说明人或事物 | stress, which is · strength which is · material, which is |
需要注意的发音
说话人用了 3 次缩略和弱读形式，例如 I'll, we've, wouldn't。请按听到的简短形式来说。
- “sh” 和 “zh” 音: deformation /ˌdɛfəˈmeɪʃən/, deflection /dəˈflɛkʃən/, sectional /ˈsɛkʃənəl/, consultation /ˌkɑnsəlˈteɪʃən/
- 长单词——注意重音位置: deformation /ˌdɛfəˈmeɪʃən/, allowable /əˈlaʊ.əbəl/, personalize /ˈpɜː.sə.nə.laɪz/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/, consultation /ˌkɑnsəlˈteɪʃən/
中文母语者容易读错的音：
- 词尾辅音 — 要读清楚，后面不要加元音: distress /dɪˈstɹɛs/, hardness /ˈhɑɹdnəs/, modulus /ˈmɑdʒələs/, stiff /stɪf/, graph /ɡɹæf/
- /r/ 和 /l/ 的区别: brittle /ˈbɹɪtəl/, embrittlement /ɛmˈbɹɪtl̩mənt/, granular /ˈɡɹæn.jə.lə(ɹ)/, counselor /ˈkaʊnsələ(ɹ)/
- /æ/ — 嘴张大，不要读成 /e/: fracture /ˈfɹæk.t͡ʃʰəː/, graph /ɡɹæf/, absorb /æbˈsɔɹb/, axis /ˈæksɪs/, granular /ˈɡɹæn.jə.lə(ɹ)/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 先用 0.75 倍速逐句跟读，熟练之后再回到正常速度。
- 录下自己的声音并与原声对比，特别注意 brittle, deformation, fracture 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。