A crack in a steel beam forced the closure of the Interstate 40 Hernando DeSoto bridge that connects Arkansas and Tennessee over the Mississippi River at Memphis. A critical beam was fractured to the point of being nearly severed. Photos of the crack appear to… Read more
Stress Concentration Factor & Crack Initiation
This photo was taken outside of my former office in Huntsville, Alabama. As newly poured concrete hardens and dries, it shrinks. This is due to the evaporation of excess mixing water. The cracks in the photo may have formed during this phase. In addition, the concrete experiences… Read more
United Airlines Flight 328
United Airlines Flight 328 was a scheduled domestic passenger flight from Denver to Honolulu, Hawaii on February 20, 2021. The Boeing 777-200 aircraft operating the route suffered engine failure shortly after takeoff. Video link The failure was “contained” but resulted in a debris field at… Read more
k factor for one-sided normal tolerance limit
Matlab script: %% k_factor.m ver 1.0 by Tom Irvine%% k factor for one-sided normal tolerance limit%% p = probability percent% c = confidence percent% nsamples = number of samples%% k = tolerance factor% Zp = Z limit corresponding to probability area in the normal% distribution… Read more
Another Method for Pyrotechnic-like Time History Synthesis for an SRS Specification
I have added an exponential decay option to the wavelet synthesis function. This arranges the wavelets so that they will “resemble” a pyrotechnic-like time history. The function is included in the GUI package at: Matlab Link Note that the conservative ramp-plateau enveloping in the SRS… Read more
Transforming Complex Mode Shapes into Real, Undamped Shapes
Modal test data processing methods perform curve-fitting on measured frequency response functions. These are indirect methods for extracting natural frequencies and damping ratios. The FRF methods also yield mode shapes which may be complex if the system has non-proportional damping. Each complex mode shape can… Read more
Material Damping
Internal friction and heat generation cause a deviation from perfect elasticity, resulting in the hysteresis loop in the stress-strain curve. The damping capacity ψ is: ψ = ΔW/W where W is the initial strain energy and ΔW is the energy lost during one cycle of oscillation. Some damping capacities… Read more
Shock & Vibration Test Fixture Design
Introduction Vibration test fixtures are the mechanical interface between the shaker system and the unit under test (UUT). Their purpose appears simple: hold the test item securely and transmit the specified vibration input. In practice, fixture design is one of the most important and often… Read more
Architectural Helmholtz Resonators
Tapiola Lutheran Church in Espoo, Finland, Opened in 1965 Helmholtz-type resonators are built into the walls of the church. The slots between brick pairs and cavities behind them act as both absorbers and diffusors of sound. The absorption reduces the reverberation time as desired for… Read more
Material Shock Loading
The plot shows the applied strain on the horizontal axis and the resisting stress on the vertical axis. The area inside the triangle represents the maximum energy that can be absorbed elastically, if the member is strained up to its proportional limit stress. The member… Read more