Integrity Assessment of LCA Drop Tank under Internal Cyclic Pressure

A facility and expertise has been developed at NAL to conduct automated internal pressure cycling tests. The hardware and instrumentation includes capturing of pressure on the data logger along with strain gage data. Digital data can be recorded continuously during entire pressure cycle, thus enabling to provide comparative view of reduction in stiffness, if any,in terms of graphs. The Maximum Pressure up To Which the Central Shells Could Be Tested Was 188 .5psi. A Maximum Strain Of 5166 Micro Strains, At A Pressure Of 188 .5psi, Was Found Near The GFRP Bulkhead In The Circumferential Direction. The Integrity Of The Bulkhead Joint Appears Satisfactory. The Nose-Cone, Tested For Internal Pressure Cycling Between 3 And L Lpsi Did Not Show Any Leaks Anywhere On The Surface Or From The Filler Cap . However, After 1104 Pressure Cycles,The End Flange Failed With A Loud Pop.On Inspection, It Was Found That The Failure Is Due To Improper Adhesion Between The GFRP Base Material And The Aluminum Ring Holding The End-Flange. Subsequently, This Ring Was Joined To The GFRP Shell By Bolts And The Pressure Cycling Was Continued For A Further 5000 Cycles,As Required, Without Any Failure/Leaks Anywhere On The Nose Cone. The Nose Cone Was Then Subjected To A Steadily Increasing Pressure To Verify The Residual Strength.At About 60psi, Leaks Were Observed Around The Filler Cap And The Pressure Was Continued Up To 85psi . At This Pressure, The Filler Cap Seal Gave-Up And A Profuse Leak Sprouted Around The Cap This Was Verified Again By Replacing The Filler Cap With A New One That Also Failed Completely At About 85psi Pressure. Presently,It May Be Concluded That The Lca s Gfrp Drop Tank Internal Bulkheads Of Central Shell Can Withstand A Pressure Of 185psi And The Weak Link,In The DT Assembly, Is The Filler Cap Seal That Can Stand A Pressure Of Only 60psi

Regulating STING in health and disease.

The presence of cytosolic double-stranded DNA molecules can trigger multiple innate immune signalling pathways which converge on the activation of an ER-resident innate immune adaptor named "STimulator of INterferon Genes (STING)". STING has been found to mediate type I interferon response downstream of cyclic dinucleotides and a number of DNA and RNA inducing signalling pathway. In addition to its physiological function, a rapidly increasing body of literature highlights the role for STING in human disease where variants of the STING proteins, as well as dysregulated STING signalling, have been implicated in a number of inflammatory diseases. This review will summarise the recent structural and functional findings of STING, and discuss how STING research has promoted the development of novel therapeutic approaches and experimental tools to improve treatment of tumour and autoimmune diseases

Spectrum Modification for Full Scale Fatigue Testing of an Ageing Aircraft

The flight load sequence of a combat aircraft was modified by eliminating different levels of small amplitude load excursions to derive several different test load sequences. The fatigue crack growth behavior under all these spectrum load sequence was predicted in a single edge notched tension specimen of an airframe grade La16 aluminum alloy. Crack growth behavior was predicted using a fatigue crack growth law derived from the constant amplitude fatigue crack growth tests, incorporating crack closure effects. It was observed that full scale fatigue testing time can be reduced significantly by using of one of the derived test load spectrum without compromising, in general, on the fatigue damage caused by eliminated load cycles

Effect of Airframe Materials on Spectrum Modification for Full Scale Fatigue Testing sf an Ageing Aircraft

In order to accelerate full scale fatigue testing, the original flight load spectrum of a combat aircraft was modified by eliminating small amplitude load excursions lower than a prefixed filter value. Different levels of filter value were used to derive several different test load spectrum having lesser number of fatigue cycles than the flight load spectrum. The fatigue crack growth behavior under all these spectrum load sequences was predicted in two different airframe materials viz., D16 aluminum and Ti6A14V alloys using a fatigue crack growth model derived from constant amplitude fatigue crack growth tests, which incorporated crack closure effects. Results show that the basis of spectrum modification should not only be the elimination of small amplitude load cycles but also on the fatigue crack growth behavior of the structural materials used in airframe construction

Cycle counting using rainflow algorithm for fatigue analysis

Rainflow algorithm is one of the widely accepted techniques of cycle counting in fatigue analysis for damage assessment in engineering components and structures. In this paper a brief summary of Rainflow cycle counting technique has been outlined. To demonstrate the efficacy of the developed Rainflow algorithm in a computer is being validated by numerous standard set of test problems simple sequences are described. An attempt has been made to illustrate the algorithm accuracy by demonstrating a number of simple examples. The examples that are included are (i) Available literature sequences, (ii) Decreasing amplitude sequence (iii) Increasing amplitude sequence and (iv) Constant amplitude sequence. Finally the results from analyzing a service load spectrum of a fighter aircraft is provided in this paper

Prediction of Optimum Spectrum for Full Scale Fatigue Test

The standard FALSTAFF flight load sequence was modified by eliminating different levels of small amplitude load excursions to derive several different test load sequences. The fatigue crack growth behavior under all these spectrum load sequences were predicted in a compact tension (CT) specimen of an airframe grade structural steel. Crack growth predictions were made using a fatigue crack growth law derived from constant amplitude fatigue crack growth tests, which incorporated crack closure effects. It was observed that fatigue tests could be accelerated by using one of the derived optimum test load sequences without any significant effects of omitted load cycles on fatigue damage accumulation in the material. The underlying mechanism for the observed growth behavior is highlighted

Numerical and experimental analysis to predict the compressive strength of pristine composite laminates

In this work, the numerical and experimental work has been carried out to verify the compressive strength of pristine composite laminates. Theoretical computations have been carried out using MATLAB to compute the strength and buckling load. Finite Element Analysis has been carried out for the composite laminate using two and three dimensional elements. PATRAN as the Pre and Post processing package and NASTRAN as the solver have been used in this work. The various failure theories considered in this article are Tsai-Wu, Hill, Hoffman, Maximum Stress and Quadratic failure theory (YSFT). All the first four failure theories are available as a standard criterion in the PATRAN package. The fifth quadratic failure criterion has been implemented using PATRAN Command Language. Static analysis along with failure theories has been carried out to compute the strength of the laminate. Static and buckling analysis has been presented for both in two-and three-dimensional models. Experiments have been carried out on number of pristine laminates and the strain values obtained from FEA have been compared with the experimental values. The theoretical computation provides a load value which is about the elastic limit of the specimen. It is generally observed that quadratic failure theory (YSFT) provides least failure indices and may be employed for conservative design

Experimental Evaluation of Laminated Carbon Composite Step Lap Repair Through Static and Fatigue Compression Loading

The static compression test is performed on various carbon fiber reinforced plastic (CFRP) epoxy-based laminate panels manufactured with the vacuum enhanced resin infusion technology (VERITy) process. These tests are conducted for establishing the compression strength and evaluation of the step-lap repaired method effectiveness. The barely visible impact damage (BVID) is simulated experimentally by impacting with low energy. The response of the pristine, impact-damaged, and step-lap repaired composite panels are captured experimentally through the online strain measurement during the testing at various locations. The predicted strain response from the finite element analysis is validated with that of the experiment for all of the specimen configuration. Reasonable good agreement is observed between the predicted and the experimental strain values in terms of their magnitude and the trend. It is observed that both of the strength and the stiffness are regained in the composite panels after the step-lap repair scheme is implemented. Constant amplitude fatigue behavior of pristine and step-lap repaired composite panels are tested under compression-compression fatigue loads. It is observed that the stiffness of both of these panels is not significantly degraded over a testing period of million fatigue cycles

An experimental study on impact behavior of quasi-isotropic CFRP laminates

This work was carried out to bring out the differences in drop weight low velocity impact behavior of two quasi-isotropic (QI) laminates. These laminates were made of AS4/914 carbon fiber reinforced plastic (CFRP). The layup sequence chosen was [0/45/-45/90]2S and [0//90/45/-45]2S. Two types of impactors were employed for the impact tests. One is a hemispherical-end and the other is of a conical-end. Coupon level specimens were supported on all four sides during the impact test. The impact energy was calculated for the laminates and the difference, as a comparison, in each case is presented. It has been observed that the layup sequence has a significant effect on the impact resistance of the laminates under hemispherical impactor. In the case of conical impactor, both the laminates were perforated while absorbing similar energy levels