Evaluation of damage within sandwich honeycomb panels subjected to impact fatigue loading

This work was aimed at investigating damage evolution within sandwich panels consisting of aluminum skins and Nomex™ honeycomb core, with three different values of the core densities, subjected to multiple impacts. Repeated impacts at low energy were conducted using an impact fatigue machine. Bending tests were conducted to determine the residual stiffness after impacts in order to analyze the evolution of a damage parameter D. A model was therefore proposed for describing the changes in this parameter as a function of impact cycles N. After repeated impacts, the D(N) curves are characterized by an S-shaped curve. A good agreement is observed between model and experimental results, the maximum standard deviation being less than 7% for different densities. Microscopic observations of the impacted specimens were conducted in order to evaluate the crater growth (associated with permanent indentation). The influence of the number of impacts on the dimensions of the impact zone has also been evaluated. For all the core densities, the permanent indentation gradually increases as a function of impact cycles.

Fatigue life assessment of TTC streetcar concrete pavements

The Toronto Transit Commission, TTC traditional embedded track for mechanically jointed rails, is performing satisfactory except for accelerated surface concrete deterioration. By far the most damaging group of deterioration processes in streetcars concrete pavement is due to wheel impact on the joints which will subsequently excite a response on the track. The enhancement of special trackwork, STW service life was the initiative to explore encapsulation technology advances in embedded track materials and construction methods. This aimed to extend the life cycle of the track from current average of 15 years towards target life of 50 years. In the present study, attempts at finding and patterning the localized cracks, especially wheel impact fatigue cracks, are carried out. This issue was investigated during the course of an experimental program demonstrated by simulating the wheel impact loading in concrete under repeated load application. Specially designed specimens were used to represent sheet rubber and urethane encapsulation system proposal against the current assembly. This research reviews the pros and cons of various factors influencing the life cycle of the current assembly and examining and assessing between alternative track construction methods and materials at the joints and examining the concrete's performance both during the impact fatigue loading resulting in inclined cracking and ongoing service life and durability issues under combined environmental and mechanical loadings. Experimental results show that it is possible to achieve the targeted service life of 50 years, based on minimum of 10 time superior performance for either of the proposed encapsulation technologies vs. current construction methods.

Fatigue life assessment of TTC streetcar concrete pavements

The Toronto Transit Commission, TTC traditional embedded track for mechanically jointed rails, is performing satisfactory except for accelerated surface concrete deterioration. By far the most damaging group of deterioration processes in streetcars concrete pavement is due to wheel impact on the joints which will subsequently excite a response on the track. The enhancement of special trackwork, STW service life was the initiative to explore encapsulation technology advances in embedded track materials and construction methods. This aimed to extend the life cycle of the track from current average of 15 years towards target life of 50 years. In the present study, attempts at finding and patterning the localized cracks, especially wheel impact fatigue cracks, are carried out. This issue was investigated during the course of an experimental program demonstrated by simulating the wheel impact loading in concrete under repeated load application. Specially designed specimens were used to represent sheet rubber and urethane encapsulation system proposal against the current assembly. This research reviews the pros and cons of various factors influencing the life cycle of the current assembly and examining and assessing between alternative track construction methods and materials at the joints and examining the concrete's performance both during the impact fatigue loading resulting in inclined cracking and ongoing service life and durability issues under combined environmental and mechanical loadings. Experimental results show that it is possible to achieve the targeted service life of 50 years, based on minimum of 10 time superior performance for either of the proposed encapsulation technologies vs. current construction methods.

Vibration-based, nondestructive methodology for detecting multiple cracks in bending-torsion coupled laminated composite beams

Damage to composite structures occurs from impact, fatigue, or over stress and can be critical in the safe operation of wings or any structural member. This paper presents a method for detection of multiple cracks present in laminated composite bending-torsion coupled cantilevered beams using natural frequency data, a type of Nondestructive testing (NDT). This methodology relies on both experimentally collected natural frequencies and frequencies calculated using a mathematical model. Precise natural frequencies are calculated using a new dynamic finite cracked element (DFCE) formulated within and based on dynamic trigonometric shape functions. An algorithm is devised based on the Adam–Cawley criterion and extended to laminated composites with multiple cracks. This method has shown exceptional convergence on the size and location of cracks using a number of modes of free vibration with and without error in measured frequencies.

Vibration-based, nondestructive methodology for detecting multiple cracks in bending-torsion coupled laminated composite beams

Damage to composite structures occurs from impact, fatigue, or over stress and can be critical in the safe operation of wings or any structural member. This paper presents a method for detection of multiple cracks present in laminated composite bending-torsion coupled cantilevered beams using natural frequency data, a type of Nondestructive testing (NDT). This methodology relies on both experimentally collected natural frequencies and frequencies calculated using a mathematical model. Precise natural frequencies are calculated using a new dynamic finite cracked element (DFCE) formulated within and based on dynamic trigonometric shape functions. An algorithm is devised based on the Adam–Cawley criterion and extended to laminated composites with multiple cracks. This method has shown exceptional convergence on the size and location of cracks using a number of modes of free vibration with and without error in measured frequencies.

Pattern of Cumulative Treatment Hours on Pain Impact and PROMIS Outcomes

ABSTRACT Introduction Participation in interdisciplinary treatments is associated with improvement in pain intensity, physical function, and additional pain-related outcome domains. However, the effect of cumulative treatment hours on outcomes remains unknown among military patients. The present analysis examined the relationship between cumulative interdisciplinary treatment hours and pain management outcomes at a single interdisciplinary pain management center (IPMC). Materials and Methods This is a retrospective observational study of data previously collected as standard of care at the Madigan Army Medical Center, approved by the Institutional Review Board. We included patients who received treatment at the IPMC and completed at least two self-report assessment batteries: one at baseline and at least one between 90 and 180 days after baseline (n = 882). The primary outcome was pain impact. Secondary outcomes included fatigue, depression, anxiety, and sleep-related impairment. Results Generalized additive models indicated that cumulative treatment hours were significantly associated with improvement in pain impact, fatigue, and depression. Patients who had higher baseline pain impact, who had mild or no depressive symptoms, and who were >40 years of age had greater improvements in pain impact following treatment, relative to those with lower pain impact, moderate-to-severe depressive symptoms, and were 40 years of age or younger, respectively. Additional research is needed to elucidate the effect of different therapies and additional patient factors in understanding the “therapeutic dose” of interdisciplinary pain management. Conclusions A higher number of cumulative treatment hours was associated with improvement of pain impact, fatigue, and depression among military personnel receiving interdisciplinary pain treatment. At least 30 hours of sustained interdisciplinary treatment appears to be the threshold for improvement in pain impact and related outcomes.

Effects of impact fatigue on residual static strength of adhesively bonded joints

In most industrial applications, adhesive joints experience impact fatigue loads in service. The energy of each impact is too low to cause joint failure. Although the repetitive impacts usually do not apparently affect the joints, they can significantly reduce the strength of adhesively bonded structures. Accordingly, understanding the effect of impact fatigue on the residual strength of the bonded components is crucial in real applications. This study deals with this issue where the effect of impact fatigue on the residual static strength of single lap joints is analyzed. To achieve this, the manufactured single lap joints were categorized into four different groups. Group 1 joints were tested under static loading conditions. Joints in group 2 were tested under impact to obtain the impact strength of the single lap joints. To analyze the impact fatigue life of the joints, the single lap joints in group 3 were tested under cyclic impact at different energy levels until failure. To investigate the effect of impact fatigue on the residual static strength of the joints, single lap joints in group 4 were tested under a specific number of impact cycles followed by a static tensile test. Using microscopic analysis, the fracture surfaces of the tested specimens were analyzed. The results showed that cracks initiate from the middle of the bonded area as a result of cyclic impact stress waves. Then, by increasing the number of impacts, a large number of cracks nucleate from the edges of the joints and grow along the width to the middle of the overlap. A 3D finite element method was employed to analyze the stress distribution along the bondline under impact loads.

M. W. Tofique, A. Löf, C. Millward, Z. Günther. Testing and calculation of impact fatigue strength of Flap-X and SS 716 flapper valve steel grades / trans from Engl. M. A. Fedorova

During the operation of reciprocating compressors, the flapper valve opens and closes under fluid pressure and flow. As it closes, it strikes against the valve seat, generating stresses and noise. This cycle of loading produces bending and impact fatigue stresses in the reed. This load pattern is repeated billions of times during the service life of a compressor and it defines the service life and reliability. The goal of this study was to calculate the impact fatigue strength of the Flap-X and the SS 716 grades and, to provide the compressor manufacturers with the information they can use to specify a steel grade to be used in their compressors, for reliable service. Impact fatigue tests were conducted on a custom-built impact fatigue test rig that used air pulses to produce movement of the reed valves manufactured by a major European compressor manufacturer Nidec Global appliance GmbH, at a frequency of 315 Hz and pulse width of 2,2 milliseconds. The testing was conducted according to the staircase test method detailed in the International Standard SS-ISO 12107:2012. The impact fatigue strength of the Flap-X and SS 716 steel valves was calculated in terms of the impact velocity according to the modified staircase test method in the standard. The test results and their statistical analysis showed that the impact fatigue strength of the Flap-X grade was higher compared to the SS 716 grade. The calculation and testing of the impact fatigue strength of the flapper valve steel grades could help the compressor designers to select the optimum material for their compressor designs, to provide reliable service. The higher impact fatigue strength of the Flap-X grade, lower failure rate and longer impact fatigue life will allow the compressor manufacturers to design thinner valves, as Flap-X can sustain higher impact fatigue stresses reliably for longer time and, at the same time help reduce noise, as thinner valves produce less noise for a given pressure and frequency.