Literature and ever since engineers and researchers

Literature Review

Struts
are being used in various industries since structures were started being built
thousands of years ago. Composites were discovered in the 1960’s and ever since
engineers and researchers are trying to move towards manufacturing lightweight
composite structures. However, its only in the last few decades that the
engineers have been paying detail to composites due to the various advantages
that are associated with composite materials. The high cost of manufacturing of
composites limits it to a few industries, Namely the automotive , aerospace and
space sector. NASA has a
continuing interest in both improving and experimentally verifying the load carrying
capability of these types of structural components to support the goal of
designing high performance, lightweight aerospace structures. (KC Wu et
al.,2011). Furthermore, since the LATP process is relatively new, there
has been little to no work done on manufacturing lightweight thermoplastic
composite struts using this process. The literature reviewed in the following
sections will cover a brief overview of struts across the industries, struts
made from composites, history and advantages of composites and the LATP
process.

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Brief overview of struts

A
strut when designed for a certain purpose should be able to withstand all
forces that are applied to it. Moreover, a strut should be designed and built
to cope with natural phenomena such as wind power, rain or phenomena such as
solar irradiance and high temperatures in space. A member in compression is
usually called a strut. However, a key aspect of this project is that the strut
should be able to carry tensile loads. Material used to manufacture the strut
is of high importance as an ideal strut should have a very high structural
efficiency.

Struts in the Automotive Sector

Struts
are used in majority of the vehicles if not all in the automotive industry.
They are used as suspensions as they absorb the continuous loads when the cars
go over the speed bumps or pot holes. Suspension system is of critical importance in the
automobile as all the driving/braking force and lateral force during cornering
are transferred to the car body from the ground though the suspension system (S
Xu et al., 2017). The struts in this industry have also been moving away
from hot rolled metals to composites because of they are lightweight as well as
strong enough to withstand harsh conditions including incredible stress and
strain. Moreover, decreasing the weight allows the engineers to improve the
vehicle dynamic performance. Under severe loads, traditional struts can be
easily deformed causing cracking and ‘mushrooming’ of the metal. A study by (S. Xu et al., 2017)
using design of experiments (DOE) helped establish the correct design
parameters to find the aspect that is more significantly changing the behaviour
of the beam spring. The results were as follows, more than 25% of the weight is
reduced and the maximum dynamic load of the CFRP strut tower was reduced by ?
50% in comparison to the metal structure. Therefore, it is evident that CFRP
strut tower has “high potential to substitute for conventional
strut tower for the prevention of failure by impulses transferred from the road
surfaces.” (Lee et al., 2014). Strut towers made from thermoplastic composites
by the LATP process could be a possibility in the future.

Struts
in the Aerospace sector

Since the birth of airplane struts have been a
critical part of this sector as they are usually found as braces attaching the
wings of aircraft to the fuselage. The Wright Flyer used a strut made of white
spruce as there are high tensile loads that are applied due to the lifting
forces on the wings and would feel compression loads when the aircraft would
execute roll, pitching moment or any other type of maneuvers. As engineers
gained more knowledge about the laws of aerodynamics they resisted from using
struts as they caused a lot of drag decreasing the overall efficiency of the
aircraft. However, in recent years, struts are found all throughout the modern
aircraft.

All structures
must be designed with care because human life often depends on their
performance. Structures are subject to one-way and oscillating stresses, the
latter giving rise to fatigue. Metal structures are subject to corrosion, and
some kinds of corrosion are accelerated in the presence of stress (Nataliya,
2003). Engineers are working
constantly on new aircraft designs always having one objective in mind to
reduce the maximum takeoff weight to make the aircraft of the future more fuel
efficient. (Amir H.
Naghshineh-Pour, 1998) undertook a study on the use of an external strut or a
truss bracing for weight reduction. One of the main goals of strut braced wing designs is
to decrease airfoil thickness and, as a result, to reduce wave drag and
increase laminar flow and fuel efficiency. Thus, reducing the weight of the
structure and increasing the fuel efficiency. The results from (Amir H. Naghshineh-Pour, 1998) the best
strut-braced wing configuration exhibited a 18% reduction in wing weight and an
9.4% reduction in takeoff gross weight compared to a cantilever wing
counterpart. Aeroelastic and structural dynamic analyses were not carried
out on the struts by (Amir H. Naghshineh-Pour, 1998) and still need to be
investigated .

Wing
braces are not the only place struts can be found in aircraft today. There are
struts located in the undercarriage of the aircraft. The landing gear is also
called the heart of the aircraft and travel would never be this comforting
without its existence. The struts in the landing gear are used to absorb and
dissipate landing impact energy and reduce airframe stresses. These
accelerations must be acceptable not only to structural components, but also to
everything contained within the aircraft. The Boeing 787 has moved to the use
of composite struts in the landing gear. The use of composites in conjunction
with expanded use of titanium provides higher resistance to corrosion and
fatigue than other metals, also contributing to greater in-service reliability
and greater time between overhauls. Cranfield University was involved in the
reinforcement of a 1.2 m long landing gear brace using a carbon thread allowing
a MTOW of 227 kN. The fibers are consolidated using resin transfer molding
injection. During the injection process, air in the mold is being replaced by
resin and the fibers are impregnated. According to a study led by (H Thius, 2004) composite
landing gear braces were impacted with 86 Joule with a spherical tub with a
diameter of 12.7 mm. After being impacted the specimens were cut and the cross
sections were examined. The test demonstrated that the titanium plates
protected the generic lug specimens sufficiently. Fig 1 presents one of the cross sections that were made. Composite
landing gear components therefore are opportunities to be taken for application
in the next generation civil and military aircraft and can also be manufactured
using the LATP

The fuselage of an aircraft serves to accommodate
payload. In a civil aircraft the fuselage would have to carry the passenger and
cargo and thus would be a load bearing member in the aircraft. The cockpit and
key aircraft systems are also located in the fuselage. In aircrafts the strut
is the support structure under the cabin floor. A research by (Y Ren et al., 2016) for the impact dynamic
performance of the aircraft with bottom sine-wave beam structure with different
rigidity of strut is studied and compared with that of conventional type. Three
different strut design concepts including the single shell with holes, single
shell and square tube are integrated with the sine-wave bottom structure by (Y
Ren et al., 2016). The largest and smallest internal energy of sine-wave beam
is the single shell with holes and square tube, respectively. The energy
absorption ability of strut is exhibited in Fig. 2. The square strut design
concept is used in this project. The LATP can be used to make composite struts
for the fuselage in the future.

With the advancement of technology and the desire of
people to travel faster many companies are working on aircrafts that can fly up
to Mach 3 or 4. They would be suitable in the business and military sector.
Turbine engines can only be efficient up to Mach 3 so researchers have been
working on Scramjets which are said to be efficient even when greater than Mach
3. However, there exists a need for development in fuel mixing and flame
holding within milliseconds. There has been plenty of research into the idea of
using struts are fuel injectors into scramjet engines. Various studies by
(Ashok De and Rahul Kumar Soni., 2016) suggest that the strut based parallel
injection is more promising, as it offers the possibility of injecting fuel into
the core of oncoming supersonic flow, leading to uniform spreading of the fuel.
In a study by
(Chandrashekhar, Ramanujachari and Reddy, 2014) the possibility of using fuel
injectors made from nimonic c-263 allow were tested and evaluated. It was found
20 second test at 2000 K that the struts were deemed to be structurally safe
which is a massive step forward for the design of scramjet engines. While
the CF/PA12 would fail at these temperatures, in the near future there will be
a suitable material that can be manufactured by the LATP process.