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Bài giảng môn Cơ Học Vật Rắn Biến Dạng ĐH Bách Khoa HCM từ chương 1 đến chương 6 Giảng viên: Trương Tich Thiện Ngôn Ngữ: Tiếng Anh Cần thiết cho sinh viên các ngành Cơ Khí, Cơ Kỹ Thuật, Kỹ Thuật Hàng Không,...
Hochiminh City University of Technology Strength of Material Chapter Internal Forces and Internal Force Diagrams Contents 1.1 The Basic Concepts 1.2 The Internal Force Components 1.3 The Internal Force Diagrams Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Hochiminh City University of Technology Strength of Material Chapter Internal Forces and Internal Force Diagrams Lecture Goals nội lực cấu trúc Internal Force in Structures – Axial Load lực dọc trục – Torque Momen xoắn – Shear Forces lực cắt – Bending Moments momen uốn Return to overview Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts 1.1 The Basic Concepts Deformable solid mechanics is a field of mechanics The force propagation, the shape variation of solid have been mentioned in this field From that point, strength, hardness and stability of body will be studied Figure 1.1 Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 4.1 The Basic Concepts Observed shape Body’s shape is divided into three types: trục giàn • Truss, beam, shaft, frame dầm khung Figure 1.2a Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts • Shell/Plate • Solid Figure 1.2b Figure 1.2c Observed shape of body is truss, beam, shaft, frame Observed material properties are small elastic, continuous, isotropic, homogeneous đẳng hướng: khả chịu lực hướng đồng chất Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts 1.1.1 The Internal Forces What use are the Internal Loads? In terms of the grand scheme of things, why we need to find the internal loads? Normal stresses are determined by the bending moment and axial force, shear stresses are determined by the maximum shear force and the maximum torsional moments NOT ALL MAXIMUM FORCES OCCUR AT THE SUPPORTS! Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts 1.1.1.1 Definition The internal forces are the interactive forces between the objects in the observed mechanical system 1.1.1.2 Observed method The cutting method is used in order to determine the internal forces The two parts of body are separated by the cross-section which is perpendicular to body axis Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts The internal forces p The external forces Figure 1.3 Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts 1.1.2 The Stress 1.1.2.1 Definition Ox,Oy hệ trục qn tính trung tâm hình phẳng A A Observe the small area A around the particle M on the section A The resultant of internal force acting on area A is P The stress acting at particle M and on section A containing M is defined as following equation: A O M x zx ứng suất P p = lim A →0 A vecto ứng suất P điểm M shear stress, // trung vs mặt phẳng zy z normal stress, z vng góc vs mp p P y Figure 1.4 (1.1) nội lực tổng tác động lên phần vi phân delta diện tích deltaA, tích phân lớp N/M^2 Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics Chapter Internal Forces and Internal Force Diagrams 1.1 The Basic Concepts The Cartesian coordinate system Oxyz is chosen so that the origin O coincides with centroid of section, the axis z is normal to the section and its positive direction is directed towards outside of section, two axes – x and y – are the centroidal principal inertia axis system of section The positive directions of axes – x and y – are chosen so that the coordinate system Oxyz on the section of left part of body complies with RHR and on the section of right part of body complies LHR Assoc Prof Dr Tich Thien TRUONG Department of Engineering Mechanics