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# 疲劳统计基础概念

The Two Basic Approaches

Figure 1: Failure Modes are Different for Static Failure, Low Cycle Fatigue, and High Cycle Fatigue.

Concepts in Common

Figure 2: Constant Amplitude Load History.

Figure 3: Variable Amplitude Load History.

Figure 4: Proportional Multiple Channel Load History.

Figure 5: Non-Proportional Multiple Channel Load History.

Fatigue Life and Fatigue Damage

Figure 7: Load Applied to a Component Induces a Nominal Stress and a Local Stress at the Notch. 名义应力：

Damage Based Methods

Data

Reduction

Rate Independent Counting Methods

Figure 10: Derivation of Counting Methods.

Data Preprocessing
Peak/Valley Filtering

Figure 11: Stress-Time History.

Figure 12: Peak-Picked Stress-Time History. Hysteresis Filtering

Figure 13: Hysteresis Filter. Discretization 把载荷幅值范围分成 N 个等间隔区间（bin），默认值 N＝100。

Rainflow Cycle Counting

Figure 14: Illustration of a Hysteresis Loop. 雨流计数最重要的优势是与疲劳损伤的一致性。

Figure 15: The 4-Point Algorithm.

Figure 16: Schematic of From-to Matrix Construction.

Figure 17: Time History.

Figure 18: Cumulative Cycle Count.

Life Curves

Introduction 试验计划由若干信号段编制而成，通常是 5 至 50 段信号，重复编排。 Fatigue Background

Non-Local and Surface Effects

The Fatigue Notch Factor

Figure 19: Comparison Between the Fatigue Behavior of an Unnotched Component Compared to a Notched Component.

What are Size Effects?
Technological Size Effects Quenched and Tempered Steel:

Figure 20: Hardness Profile in Tempered or Quenched Steel. High Strength Steel: 非金属杂质颗粒的大小，形状和分布影响疲劳寿命。表面越大，出现杂质颗粒的 概率越大。

Figure 21: Stress Distribution in High Strength Steel Due to Non-Metallic Inclusions. Size Effect of Surface Treatment 表面强化的相对深度取决于零件尺寸，并且影响内层的预应力。

Figure 23: Different Pre-Stresses at the Inner Layer After Surface Treatment.

How to Account for Size Effects

Neuber’s approach to micro-yielding

Surface Effects

Figure 30: Correction Factors Due to Surface Roughness. 表面修正系数为

.

The Statistical Nature of Fatigue

Figure 31: The Likelihood of Weak Components Subjected to High Loads is Minimized in a Probabilistic Design Approach. SN 曲线的臵信度通常取 10%, 50%, 和 90%的失效概率。 分散度指标是失效概率 90%和 10%对应的载荷比：

Property Influencing Fatigue Typical Scatter Manufacturing geometry Material: controlled Material: welded Applied loads 1.02 1.15 1.45 2.00

Figure 32: S-N Curve of a Material as Determined from Test Data for the 10%, 50%, and 90% Failure Probability Levels.

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