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
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
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
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
Some San Francisco Bay Area residents from Marin County to the Presidio have noticed a sustained, series of high-pitched tones. The sound reached a new peak volume, and recordings of the eerie noise spread across social media in early June,. The sound is due to… Read more
PV = pseudo velocity The following method is intended for components which are to be tested to power spectral density (PSD) specifications on shaker tables. The method can be applied to sine-on-random specifications as well. The purpose of this document is to recommend velocity severity… Read more
Liquid fuel rocket engines undergo hot fire testing before flight in order to verify their performance, design integrity, etc. The engines are mounted to heavy-duty, immovable stands for this purpose. These tests are also referred to as static fire tests. Furthermore, the tests are almost… Read more
Catholic Prayer Lord Jesus Christ, I consecrate myself today anew and without reserve to your divine Heart. I consecrate to you my body with all its senses, my soul with all its faculties, my entire being. I consecrate to you all my thoughts, words and… Read more
Revelations 1 [8] I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty. [11] Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write… Read more
[6] For the LORD thy God blesseth thee, as he promised thee: and thou shalt lend unto many nations, but thou shalt not borrow; and thou shalt reign over many nations, but they shall not reign over thee. [7] If there be among you a… Read more