Core Viewpoint - The article provides a comprehensive guide on material selection based on various mechanical properties such as Young's modulus, strength, and cost, emphasizing the importance of choosing the right materials for specific applications. Group 1: Young's Modulus and Density - When hard materials are needed, such as for top beams or bicycle frames, materials at the top of the chart should be selected [2] - For low-density materials, such as packaging foam, materials on the left side of the chart are recommended [2] - Finding materials that are both rigid and lightweight is challenging, and composite materials are often a good choice [3] Group 2: Young's Modulus and Cost - For hard materials, the top materials in the chart should be chosen for applications like top beams and bicycle frames [14] - For low-cost materials, those on the left side of the chart are preferred [14] - If a cheap and hard material is required, materials in the upper left corner of the chart, mostly metals and ceramics, should be selected [15] Group 3: Strength and Density - The strength indicated in the chart refers to tensile strength, with ceramics showing compressive strength [26] - High-strength and low-density materials are located in the upper left part of the graph [26] - Strength is a critical indicator of a part's ability to resist failure under load [26] Group 4: Strength and Cost - The strength indicated is tensile strength, except for ceramics which indicate compressive strength [38] - Many applications require materials with high strength, such as screwdrivers and seat belts, but these materials are often expensive [38] - Only a few materials can meet both strength and cost requirements, typically found in the upper left part of the chart [38] Group 5: Strength and Toughness - The strength indicated is tensile strength, while ceramics indicate compressive strength [50] - Typically, materials with poor toughness also have low strength; increasing strength may reduce toughness [50] - Strength measures a material's ability to resist external forces, while toughness measures its ability to absorb energy before failure [50] Group 6: Strength and Elongation at Break - Ceramics have very low elongation at break (<1%); metals have moderate elongation (1-50%); thermoplastics have high elongation (>100%) [61] - Rubber exhibits long-term elastic elongation, while thermosetting polymers have low elongation (<5%) [61] Group 7: Strength and Maximum Working Temperature - The chart applies to components used in environments where working temperatures exceed room temperature, such as cookware and automotive parts [73] - Polymers have lower maximum working temperatures, metals have medium, and ceramics can withstand very high temperatures [73] Group 8: Specific Strength and Specific Stiffness - Specific strength is defined as strength divided by material density, while specific stiffness is stiffness divided by material density [84] - High strength and high stiffness usually coexist, as they largely depend on the bonding forces between atoms [84] Group 9: Resistivity and Cost - The chart is primarily for selecting materials that require low prices and good electrical insulation or conductivity [97] - Good electrical conductors are typically good thermal conductors, while good electrical insulators are good thermal insulators [97] Group 10: Recyclability and Cost - The chart identifies materials' recyclability features, especially for expensive and recyclable materials [108] - Metals are particularly suitable for recycling due to ease of sorting and remelting, while ceramics are rarely recycled [108] Group 11: Production Energy Consumption and Cost - The energy consumed in producing a material is a factor in raw material costs, with most materials located in the low-cost/low-energy or high-cost/high-energy quadrants [121] - Metals often require significant energy for extraction, such as aluminum production consuming a substantial portion of total energy in the U.S. [123]

Core Viewpoint - The article discusses the historical development of aviation, highlighting key figures and technological advancements that have shaped the industry over time. Group 1: Historical Milestones - The ancient Chinese had dreams of flying, as evidenced by historical artifacts like the Dunhuang murals [4] - The first powered flight was achieved by the Wright brothers in 1903, marking the beginning of modern aviation [7] - Chinese aviator Feng Ru created two aircraft models and conducted test flights in China, but tragically died in a crash in 1912 [12] Group 2: Engineering Challenges - Early aviation safety considerations focused on structural integrity, such as wing strength and fuselage durability [13][17] - Engineers used sandbags to simulate aerodynamic loads during ground tests due to the lack of advanced technology [16] - The concept of strength refers to a structure's ability to resist failure under load [17] Group 3: Aircraft Design and Safety - Lift is generated by the pressure difference between the upper and lower surfaces of the wing as it moves through the air [20] - Aircraft can experience vibrations and structural deformation during high-speed flight, necessitating a focus on wing stiffness [26][28] - Historical aircraft like the DC-3 and the Comet faced structural failures due to material fatigue [29][31] Group 4: Material Science and Testing - The introduction of fatigue testing and damage tolerance concepts has improved aircraft safety [59][62] - Modern aircraft design utilizes advanced materials like carbon fiber composites, which offer high strength-to-weight ratios [78][79] - Testing methods have evolved to include simulations and dynamic load tests to ensure structural integrity [88][90] Group 5: Human Factors and Operational Safety - Human error accounts for 70% to 80% of aviation accidents, highlighting the importance of training and technology in mitigating risks [93] - Modern aircraft employ advanced flight control systems that reduce the likelihood of pilot error [97] Group 6: Future of Aviation - The future of aviation is expected to integrate air and space travel, with advancements in high-speed vehicles that could redefine distance and travel time [130][131]

Group 1 - The core idea of the research is that eggs are more resilient when dropped horizontally rather than vertically, challenging the common belief that vertical drops are safer [1][2]. - The study involved 180 egg drop experiments, testing 60 eggs from small heights, revealing that over 50% of eggs broke when dropped vertically from just 8 millimeters, while less than 10% broke when dropped horizontally [2]. - The research highlights the importance of understanding material properties such as stiffness, strength, and toughness, indicating that while vertical drops may seem harder, horizontal drops allow for greater energy absorption before breaking [2]. Group 2 - The implications of this research extend beyond eggs, providing insights for engineering applications, particularly in designing lightweight yet strong materials for aircraft, protective gear, and earthquake-resistant buildings [3]. - The study serves as a reminder that scientific experiments can lead to significant advancements in material science and engineering, showcasing the potential for innovative designs inspired by natural structures [4].