Bài giảng Vật liệu học - Chương 4: Tính chất cơ - Nguyễn Văn Dũng

1 Chương 4 Tính chất cơ 1. Khái niệm • VL thường chịu tác dụng của lực khi sử dụng • Tính chất cơ của VL xác định biểu hiện của VL dưới tác dụng của ngoại lực. • Đáp ứng của VL với ngoại lực phụ thuộc vào:  Loại liên kết.  Sự sắp xếp của nguyên tử trong cấu trúc VL.  Loại và số lượng khuyết tật. • Tính toán:  Giá trị lực  Biến dạng của VL như một hàm theo lực, thời gian, nhiệt độ, • Tính chất cơ thể hiện qua các phép thử cơ học (theo các tiêu chuẩn: ASTM (American Society for Testing and Materials), ISO (International Organization for Standardization)) CuuDuongThanCong.com https://fb.com/tailieudientucntt 2 CuuDuongThanCong.com https://fb.com/tailieudientucntt 3 CuuDuongThanCong.com https://fb.com/tailieudientucntt 4 CuuDuongThanCong.com https://fb.com/tailieudientucntt 5  Ứng suất=Lực / diện tích Ứng suất kéo Ứng suất trượt 4 • Tensile stress, s: • Shear stress, t: s  Ft Ao original area before loading Stress has units: N/m2 or lb/in2 CuuDuongThanCong.com https://fb.com/tailieudientucntt 6 • Tensile strain: • Lateral strain: • Shear strain: /2 /2 /2 -  /2 /2 /2 L/2L/2 Lo wo  = tan  Strain is always dimensionless.  Độ biến dạng CuuDuongThanCong.com https://fb.com/tailieudientucntt Tensile load Compressive load Shear strain  = tan  Torsional deformation angle of twist, f o s  F A Stress (s) for tension and compression Strain (e) for tension and compression Shear stress o t  Fs A CuuDuongThanCong.com https://fb.com/tailieudientucntt  Mô đun đàn hồi E (Young’s modulus, modulus of elasticity) Định luật Hooke (Hooke's Law): s = E e CuuDuongThanCong.com https://fb.com/tailieudientucntt 9 5 • Simple tension: cable o s  F A • Simple shear: drive shaft o t  Fs A Note: t = M/Ac Ski lift (photo courtesy P.M. Anderson) ỨNG SUẤT TRONG CÁC TRƯỜNG HỢP THỰC TẾ CuuDuongThanCong.com https://fb.com/tailieudientucntt 10 Canyon Bridge, Los Alamos, NM 6 • Simple compression: Ao Balanced Rock, Arches National Park Note: compressive structure member (s < 0 here). (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) CuuDuongThanCong.com https://fb.com/tailieudientucntt 11 7 • Bi-axial tension: • Hydrostatic compression: Fish under waterPressurized tank sz > 0 s > 0 s < 0 h (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) CuuDuongThanCong.com https://fb.com/tailieudientucntt 12 CuuDuongThanCong.com https://fb.com/tailieudientucntt 13 F  bonds stretch return to initial 2 1. Initial 2. Small load 3. Unload Elastic means reversible! BIẾN DẠNG ĐÀN HỒI (ELASTIC DEFORMATION) CuuDuongThanCong.com https://fb.com/tailieudientucntt 14 1. Initial 2. Small load 3. Unload Plastic means permanent! F  linear elastic linear elastic plastic BIẾN DẠNG DẺO (PLASTIC DEFORMATION (METALS)) CuuDuongThanCong.com https://fb.com/tailieudientucntt 15 ĐƯỜNG CONG ỨNG SUẤT-BIẾN DẠNG (STRESS-STRAIN CURVES) • Typical tensile specimen 9 • Other types of tests: --compression: brittle materials (e.g., concrete) --torsion: cylindrical tubes, shafts. • Typical tensile test machine CuuDuongThanCong.com https://fb.com/tailieudientucntt 16 CuuDuongThanCong.com https://fb.com/tailieudientucntt 17 KÉO NÉN CuuDuongThanCong.com https://fb.com/tailieudientucntt 18 CuuDuongThanCong.com https://fb.com/tailieudientucntt 19 Biến dạng đàn hồi Biến dạng dẻo CuuDuongThanCong.com https://fb.com/tailieudientucntt 20 CuuDuongThanCong.com https://fb.com/tailieudientucntt 21 CuuDuongThanCong.com https://fb.com/tailieudientucntt 22 22 • Modulus of Elasticity, E: (also known as Young's modulus) • Hooke's Law: s = E e • Poisson's ratio, n: metals: n ~ 0.33 ceramics: ~0.25 polymers: ~0.40 Units: E: [Mpa, GPa] or [psi] n: dimensionless CuuDuongThanCong.com https://fb.com/tailieudientucntt CuuDuongThanCong.com https://fb.com/tailieudientucntt 24 • Elastic Shear modulus, G: 12 t 1 G  t = G  • Elastic Bulk modulus, K: • Special relations for isotropic materials: P P P M M G  E 2(1 n) K  E 3(1 2n) simple torsion test pressure test: Init. vol =Vo. Vol chg. = DV OTHER ELASTIC PROPERTIES CuuDuongThanCong.com https://fb.com/tailieudientucntt 25 CuuDuongThanCong.com https://fb.com/tailieudientucntt 26 CuuDuongThanCong.com https://fb.com/tailieudientucntt 27 CuuDuongThanCong.com https://fb.com/tailieudientucntt 28 CuuDuongThanCong.com https://fb.com/tailieudientucntt 29 CuuDuongThanCong.com https://fb.com/tailieudientucntt 30 CuuDuongThanCong.com https://fb.com/tailieudientucntt 31 CuuDuongThanCong.com https://fb.com/tailieudientucntt 32 CuuDuongThanCong.com https://fb.com/tailieudientucntt 33 CuuDuongThanCong.com https://fb.com/tailieudientucntt 34 CuuDuongThanCong.com https://fb.com/tailieudientucntt 35 CuuDuongThanCong.com https://fb.com/tailieudientucntt 36 CuuDuongThanCong.com https://fb.com/tailieudientucntt 37 CuuDuongThanCong.com https://fb.com/tailieudientucntt 38 CuuDuongThanCong.com https://fb.com/tailieudientucntt 39 CuuDuongThanCong.com https://fb.com/tailieudientucntt 40 CuuDuongThanCong.com https://fb.com/tailieudientucntt 41 CuuDuongThanCong.com https://fb.com/tailieudientucntt 42 CuuDuongThanCong.com https://fb.com/tailieudientucntt 43 CuuDuongThanCong.com https://fb.com/tailieudientucntt