Passive Safety Flashcards
(95 cards)
1
Q
Can we use real people in car crash research?
A
•No, this is usually not possible!
- There are exceptions
- Volunteers at sub injury severity
- Field accident research
2
Q
Which are the important properties of the dummy to make it:
Replicate human response
Predict injury risk
Practical in the lab
A
Anthropometry Bio-fidelity Repeatability Reproducibility Sensitivity Instrumentation Durability
3
Q
What does Anthropometry mean?
A
It means that the size of the dummy and the mass and mass distribution of all the dummy segments must be representative of those of a human body.
4
Q
What does Bio-fidelity mean?
A
It means that the stiffness of the surface and of the different joints must be representative of those of a human body in order to give a realistic motion and interaction with the car interior.
5
Q
What does Repeatability mean?
A
It means that the dummy should give exactly the same response every time it is exposed to identical test conditions.
6
Q
What does Reproducibility mean?
A
It means that two dummy individuals should give exactly the same response every time they are exposed to identical test conditions.
7
Q
What does Sensitivity mean?
A
It means that the dummy response should be sensitive to input that affects the injury risk.
It should on the other hand be insensitive to confounding input, like for instance temperature, that does not affect the injury risk.
8
Q
What does Instrumentation mean? (Dummy)
A
It means that the dummy should be instrumented to measure output signals that are known to indicate injury risk.
These signals could be for instance accelerations, deflections or force measurements
9
Q
What does Durability mean?
A
It means that the dummy should withstand severe crash loading without damage.
A dummy that breaks during an expensive destructive crash test may make the test results invalid which usually means loss of time and money.
10
Q
There are three “sizes” of the Hybrid III dummy, which are they?
A
5 %-ile, female
95 %-ile, male
50 %-ile, male
11
Q
What is the HYBRID III dummy constructed of?
A
Metal skeleton
Vinyl (PVC) foam
Vinyl (PVC) skin
Rubber neck and lumbar spine
12
Q
The HYBRID III has a drawback regarding the seatbelt, what is the drawback? Also, it has two other drawback when compared to a real human, which?
A
The large chest, seatbelt slides off.
The geometry and the deformation properties of the Hybrid III ribcage are not representative of those of the human.
The Hybrid III thoracic spine is completely rigid and the back shape differs from that of a human.
The interaction with the seat-back and the seated posture are influenced.
The ability to bend over the shoulder belt and the mobility of the head are limited
13
Q
There is another dummy developed to be more alike a person, what is it’s name?
A
THOR
14
Q
The THOR dummy has an improved chest and spine compared to the HYBRID III, how is it improved?
A
Improved spinal shape, bending flexibility and rib cage geometry. Ability to change pitch of spine.
15
Q
What is the main instrumentation inside a dummy?
A
- Accelerometers
- Load cells
- Displacement transducers
16
Q
What is FMHF?
A
Free Motion Head Form
The “gun” that can shoot a dummy head.
17
Q
How is the HYBRID III child dummy created?
A
Just a scaled version of a big dummy.. Not very good
Jag har för mig han sa det iaf?
18
Q
Why do we measure?
A
Monitoring Processes
Control Processes and Operations
Experimental engineering analysis
19
Q
Steps to achieve good measurements?
A
Full documentation
Calibrate systems
Repeated measurements by independent groups.
20
Q
Name some automotive sensors
A
Steering sensor Throttle position sensor Fuel level sensor Mirror sensor Chassis level sensor
21
Q
Displacement sensor
A
Resistive potentiometer
22
Q
Strain Gauge
A
Resistance changed based on extending force in the sensor.
23
Q
Accelerometer
A
Piezoelectric material placed inside fixed housing.
24
Q
Describe the ideal transducer
A
No mass No volume Measure at one point in one direction Only measuring quantities of interest DC to inf. frequency response.
25
How do you measure changes in resistance?
The Wheatstone bridge
26
Why do we filter signals?
Reduce noise
Comparison of data in standardized format
Enable peak value assessment
27
How to protect from electrical noise?
Shielding
Stop band filtering
Differential measurements
28
Volvo: Circle of Life
```
Product development
Prototypes
Testing (Feedback)
Production
Real World accident data
Safety requirements
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29
Why CAE in product development?
Early Phases: Evaluate Concepts
Development Phase: Confirm status and suggest changes
Verification Phase: Quick tool for countermeasures
30
How is CAE used?
```
Crashworthiness and safety
Strength and durability
NVH (?)
Vehicle Dynamics
Aerodynamics
Powertrain simulations
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31
Crash Simulation runtime at Volvo
10 Milj elements, 30h Runtime @ 480 cores
32
Problem with CAE?
Can't capture all phenomena, but it's getting better each year.
33
Explain Biomechanics
* Application of principles of mechanics to biological systems
* Extends classical applied mechanics to living materials with peculiar constitutive equations and complex geometries
34
Explain Injury biomechanics
Study of the (mechanical) behaviour of the human body under extreme injury producing loading conditions
35
What is the purpose of the skeleton in the body?
1. Support
2. Protection
3. Movement
4. Mineral Storage
5. Blood Cell Formation
36
What is bone sensitive to?
A fast loading rate
37
Name three types of joints
* Fibrous Joints
* Cartilaginous Joints
* Synovial Joints
38
What is the most common skeletal joint?
Synovial Joints
* Distinguished by synovial cavity containing fluid
* articular cartilage
* synovial membrane
* fibrous capsule
39
What is the purpose of the muscles?
1. Movement
2. Protection
3. Posture
4. Stabilizes
5. Heat
40
Name the three types of muscles
* Skeletal muscles
* Smooth muscles
* Cardiac muscles
41
Name some Muscle Injuries
* Lacerations
* Perforation
* Rupture
* Contusion (bruising)
42
What characterizes the properties of human tissues?
* Composite structure
* Complex material models • Nonlinearity
* Viscoelasticy
* Anisotropy
* Individual spread
• Mechanical properties influenced by age, age, gender, genes, hormones etc.
43
Describe Injury Criterion
An injury criterion is the relation between the severity of an injury and the value of a physical variable describing the impact of violence
44
Explain Biological Variation
A given injury criterion
can vary from one individual to another for the same violence of impact; the consequence of an accident are usually more serious for an old than for a young person.
45
Give example of restraint systems in vehicles.
Airbag, Seatbelt, Beltingbag, Cyclist Airbag
46
Autoliv: Circle of Life
1. Crash Statistics
2. Deep crash studies
3. Biomechanics
4. Find best safety solution
5. Validation
47
Three fundamental ideas behind the seatbelt?
1. Load the strong parts of the body, pelvis & chest.
2. Maximize time-duration of applied force.
3. Maximize area of restraining force.
48
What does the load limiter in the seat belt do?
Makes sure that the entire interior distance is used when protecting during a crash. (Fördela energin över en längre sträcka --> mindre påfrestningar)
49
Why is the pretensioner necessary in a seatbelt construction?
The faster you couple the person to the vehicle, the better. --> Less peak forces on occupant.
50
Belt bag, benefit & drawback.
Benefit: 140mm better force distribution than 3-point.
Drawback: 80mm No effect comp. to 3-point.
51
Wide belt, benefit & drawback.
Benefit: For Thums-dummies wide belt is good.
Drawback: For Hybrid 3, no difference from 3-point.
52
Criss-Cross, benefit.
Good for reducing chest extersion.
53
4-point-belt, benefit & drawback.
Benefit: Good for reducing chest extersion.
Drawback: Neck heavily affected.
54
Whats important when children are using vehicle constraints?
Boost cushion.
55
Why is an adaptive airbag important?
Diversity of occupants, age, gender, size.
| Behaviour in cabin, position, belt?
56
List the most important restraint systems for Pedestrian-, Frontal-, (Near)Side- (Far)Side- Accidents.
Pedestrian: Pedestrian airbag under the hood.
Frontal: airbag, seatbelt.
Near side: Problem: High forces close to occupant. Intrusion.
Seat Airbag + Pre-Crash Airbag and inflatable curtain.
Far side: Problem: Sholder belt might slip of.
Far side airbag, protect against other occupants and interior.
57
Give examples of countermeasures for the following injury control strategies:
1. Accident Conditions
2. Crashworthiness
3. Occupant motion
4. Impact contact
1) Introduction of road mid-barriers, Accident mitigation by autonomous braking
2) Improved crush zone in the car front structure
3) Improved occupant kinematics by belt pretension
4) Improved occupant loading by the introduction/improvement of airbags
58
Describe the purpose of the H-point manikin.
Correct seat adjustment and definition of the H-point position that will determine
the dummy position in a crash test.
59
Why does the neck of the THOR-dummy replicate the human neck behaviour better than for example the hybrid III-dummy?
The THOR neck is softer in forward protraction/translational motion but it still has a biofidelic stiffness in forward angular head motion due to the muscle substiturtes anterior and posterior of the neck.
60
Give an example of a test situation where the neck biofidelity is essential for the interpretation of the test results
A biofidelic head interaction with the frontal airbag requires a realistic contact speed and impact trajectory.
61
Explain Langrarian mesh
Lagrangian mesh – moves with the material and is typically used for structural parts in crash simulations.
62
Explain Eulerian mesh
Eulerian mesh – fixed in space and material moves through the mesh, typically used in simulation of material flow, for instance in Computational Fluid Dynamics (CFD).
63
Explain Arbitrary Lagrangian Eulerian mesh
Arbitrary Lagrangian Eulerian (ALE) – A combination of both Lagrangian and Eulerian elements, for instance used for simulation of airbag inflation.
64
Why does the critical time step need to be controlled in explicit finite element simulations
Because the Central Difference Method used for the explicit time integration is conditionally stable with a requirement that the time step is smaller than the critical time step
65
Which material and geometry parameters affect the critical time step for a simulation
The critical time step is proportional to the characteristic length and wave speed of an element. The wave speed is proportional to Young’s modulus and the density of the material
66
How can the critical time step be increased without changing the geometry? Mention potential drawbacks of your proposed method.
The critical time step can be increased by locally increasing the density for small elements – mass scaling. However, mass scaling alters the mass of the problem and will have an effect on the solution and therefore engineering judgment must be used to avoid unreasonable results. Another possibility is to reduce the stiffness of the material, but this will of course lead to a softer response.
67
Name three different systems for certification
Self certification (USA) - No government involved. No approvals.
Type approvals (Europe) - Government present and issuing approvals.
Certification (Japan,Australia) - Government partly present, issuing approvals.
Compliance is verified by compliance tests.
If non-compliance - recall (Very costly)
68
Name three rating programs
Crash performance - Rating bases on crash testing
Field rating - Based on real life accidents
Evaluations - Based on experts evaluations.
69
Legal requirements can be divided into three categories depending on their national applicability. State the three categories.
International requirements (UN-ECE, EEC-directives)
National requirements
State and province requirements
70
State and shortly explain at least three of the characteristics of legal requirements.
Legal requirements must be:
- Objective
- Technology neutral
- Repetable/Reprodicable
- Be representative for safety field performance
71
Describe what types of data you can get from an in depth study of an accident.
Injuries, vehicle speeds and trajectories,residual car deformations, restraint use.
72
What methods can be used to reconstruct the accident? What additional information can be obtained by reconstruction?
- Crash test, crash simulation, pre-crash simulation
| - Vehicle accelerations, Dynamic deformations, Occupant kinematics, Occupant loading, dynamic restraint performance
73
Explain the difference between and Lagrangian and an Eulerian mesh, and give one example for which purpose each type of mesh is suitable
A Lagrangian mesh follows the material, while the Eulerian mesh is fixed in space. Lagrangian meshes are typically used for solid mechanics problems such as crash simulation, while Eulerian meshes are typically used for computational fluid dynamics simulations (CFD).
74
The Central Difference Method used for explicit FE is conditionally stable. Explain what this means and describe the stability criterion for a crash simulation (i.e. an explicit FE solid mechanics problem)
The conditional stability of the CDM means that for too large time steps the solution diverges from the actual, and typically exhibits an unbounded oscillatory response. The stability criterion for the CDM that the time increment (time step) must be smaller than the time it takes for a pressure wave to travel through the smallest element in the mesh. The velocity of a pressure wave in a solid is the same as the velocity of sound in the material, and hence the critical time step of a solid mechanics CDM simulation is proportional to le/ce, with the le = characteristic length of smallest element and ce= velocity of sound in the material.
75
Explain the concept of an initial penetration in a FE contact definition and why it is detrimental for a simulation
An initial penetration in a contact means that at the first time step of the solution, the contact surfaces has already penetrated into each other. This can lead to stability problems as large instantaneous contact forces can be created if the combination initial penetration and stiffness of the contact yields a large force, causing the nodes to “shoot out”. If part of the contact surface is on the wrong side of its slave/master partner, its nodes can also become locked in the contact.
76
Describe the primary mechanisms by which airbags protect occupants?
Head/Face contact mitigation
Load Sharing
Force Distribution Work
77
Explain the difference between how a potentiometer and a strain gauge detects a change in position
A potentiometer provides a change in voltage when the resistance of the circuit is changed because the current passes through more or less length of resistive material (ΔR=ρΔL/A). A strain gauge changes its resistance due to both a change in the cross sectional area of the conductor (geometric effect) and due to a piezo resistive change of resistance (as the material is strained it provides more resistance to electrical current).
78
Mention at least three possible functions of a bridge amplifier
A bridge amplifier typically provides an excitation voltage to the transducer, possibly does bridge completion if necessary, amplifies the signal from the transducer, and performs and initial low pass filtering of the signal.
79
Dynamic crash simulations are in general performed using either a Multibody Dynamics (MBD) or a Finite Element (FE) approach. Briefly explain each of these methods
In a MBD approach, the system to be simulated is represented by a system of rigid or flexible bodies whose motion is determined the mass and inertia of the bodies, and any constraints that affect their motion. In the FE approach the geometry is discretized in to a finite number of element and the governing differential equations for the problem at hand is solved using approximating functions on each of the elements.
80
Give two examples of phenomena that requires crash analysis to be performed using non linear methods
Material non linearity, large rigid body rotations, large rigid body rotations and large strain problems.
81
A rule of thumb for explicit FE simulations is that no more than 10% hourglass energy with respect to peak internal energy is allowed. Explain why
Hourglass energy is a non physical quantity that is added in order for the numerical solution to be stable even though under integrated elements are used. Therefore a large amount of hourglass energy in a simulation is a sign of a poor representation of the real world physics and it becomes questionable if the results from the simulation can be trusted.
82
Name three key parameters that influence compatibility.
Mass, stiffness, and structural interaction (or geometry) are the key
compatibility parameters.
83
Give 5 examples of different full vehicle test set ups
| and what types of real world collisions they resemble.
1. Rear Impact moving barrier – rear impact
2. Side Impact 90 degrees moving barrier side impact target vehicle
stationary
3. Side Impact crabbed moving barrier side impact target vehicle in motion
4. Frontal impact small overlap rigid barrier – Frontal impact cat to car
small overlap
5. Full overlap frontal impact rigid barrier – car to car 100% overlap
84
There are three different levels of crash data, which ones?
Macroscopic level - Police
Intermediate - Insurance
Microscopic - Field Investigation
85
Quickly describe the INTACT project at Chalmers
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Collecting crash scene data
Responded to ambulance calls
Passenger car, bus or truck.
Alot of variables filled in
Later simulated
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86
Exposure Data.
A measurement of to what degree road users are exposed to risk of crashes/injuries.
87
Exposure: The number of accidents in a region are often normalized by these three measures.
Population, # reg. vehicles, vehicle km traveled.
88
Terms: Confounding
The results are influenced by some important parameter that we did not take into account.
Example HIC based on length. Gender have effect.
89
Terms: Stratification
A way to control for confunding. Divide material into homogenous groups (strata).
90
Terms: Validity
What information is most relevant to rely on. Hospital reports on injuries are more valid than police reports.
91
What is the most important property of the bullet vehicle in a side impact?
Geometry, not to load high up.
| Mass and stiffness not that important since the side of the car is already very much softer than the car front.
92
FEM: Mesh quality requirements:
det (J) < 0.7 for solids
Internal angels 30 < theta < 140 for hexa elements
Aspect ratio < 3
93
FEM: A problem is dynamic if...
Frequency of applied loading is > w/5
Mass inertia affects the respondse
Time-history response is important.
94
FEM: Ex of Static simulations...
Coat hanger
Deformation due to loading
Crack propagation.
95
FEM: Ex of dynamic simulations...
Automotive crash
Paper clip bending
Bridge (windloads)
