introduction
light wirght design
means creating something that does what it needs to do
considering factors like technology,cost,enviroment and society, while making it as light as possible without sacrificing reliablitu
advantage of multi material design
optimal use of material
new and combined property profiles
good cost benefit ratio
hight lightweight potential
functional integration
improved physical and chemical properties
repair capability
platform strategy
challenge of multi material design
increase complexity in car body corresion
material seperation after cycling
complex
joining and processing
behicle co2 emission
minor:
vehicle production,disposal
major:
use phase,material production
mmp approach
material
methods
processes
efficient and sustainable lightweigth soluyion are based on a holistic understanding
composite properties,why comp
low spesific weight
high strength
required physical properties
cost resons
properties can be costomise
corresion reistance
defination composit
macrospically quasi homogenous
distinction between filler and reinforcement
adjustable properties for specific application
heterogeneous material consisting of at least two or more than non mutually soluble component
afvantage of composite
low density
high stiffness and strength
very good fatig behavor
high abillity of functional integration
low thermal expansion
low thermal and electrical conductivity
very good corrosion resistance
disadvantage
low damage tolorance
need to experties for design and dimensioning
temprature and heat stability and sensitivity compared to metal
mostly high cost
for carbon and aramid fibers
mechanical properties of composite
matris stiffness,strength>fiber
matris elongation at break>fiber elongation at break
fiber volum fraction must be above a critical value
interfacial strength >shear strength of matrix
interlaminar strength is determined by matrix properties
high important mechanical properties fiber/matrix
fiber:stiffness,strength,fatigue behavor,impact behavor,thermomechanical properties
matrix:damage tolerance
physical proerties importance
matrix: temperature resistance,chemical resistance
why actual strength of material is much smaller than the theoretically calcullated
micro void
lack of interface adhesion
paradox of fiber
material in fiber form has a much higher strength than the same material in other form
the thiner the fiber ,the higher strength
clamping paradox
the strength of a fiber seems higher when the clamping (gauge length) is shorter
slayter composite paradox
in conposite material can handle more stress together than each part alone.
bcs the strong part of the comps help componsate for weak part.
influence of matrix
important for thermal and mechanical properties as well as physical and chemical pro
influence filler
allow manipulate of the propery profile
mostly improvement of one properties at the expences of other
materil type
thermosetting and thermoplastics
thermoplastics are increasingly gaining importance
task of matrix in compos
start and transfer forces between fibers
maintain the shape of the part
keep the fiber stick together with minmum distance
balance heavy load
protecting the fiber from enviromental influences
criteria for selection material
material,process
for process:curing behaviour,processing time,viscosity
for material:resistance ,reaction to fire,fracture,electrical and mechanical proper
temprature limit
fiber volum content
varies based on type and arrangement of fiber
is crucial for sizing component
is hard to measure accurately
needed for standardizing test specimens.
stress transmission single fiber model
the force is transmitted to the fiber via shear stress.
aspect ratio
properties of fiber and matrix
ratio of E(matrix) to E(fiber)
to use fiber strength they need to be long enough to bear loads until they break
fiber reinforcement
increase stiffness:l<Lcrit
improve resistance L>=Lcrit
failuer in compositr
fiber can detach from resin,causing it to slide
fiber can be pull out
matrix can be break,either in a brittle or ductile way
fiber can break,especially in brittle material
fiber pull out
too much ahdesion between fiber and matrix is not always good
a moderate adhesion can help compoiste absorb more energy during impact by fiber pull out
energy absorption depends on fiber length and diameter ,as well as shear stress in the interface
influence of fiber orientation(continuse)
isotropic: metal behave the same in all directio,material consept and design is seperate
anisotropic: material concept and design are coupled,in laminate behavoir depends on fiber direction
posibblity for improvement of fiber matrix coupling
coating of fiber with coupling agent
chemical and physical treatment
coating fiber by coating
improve interface between fiber and matrix chemicaly
agent group can be added during mixing
for thermoplastic:mah. thermoset:silane
chemical and physical surface treatment
removal of the weakend fiber surface or impurites
adding chemical reactive group to the fiber surface
improve of surface structure
improve of fiber wetout
fiber matrix coupling with aramid fiber
no coupling agent available.aramid is chemically inert.
mechanical coupling is hardly possible
sizing of fiber,serves mainly as protection
the accumulation of reactive group by plasma treatment was successfuly tested.