1. Tipos de falla by ert554898

VIEWS: 44 PAGES: 34

									2. Tipos de falla
ANÁLISIS DE FALLAS


      CLASIFICACIÓN: 3 CATEGORÍAS
      1. MANIFESTACIÓN (FORMA DE
         PRESENTARSE)
      2. AGENTE CAUSANTE
      3. LOCALIZACIÓN
1. MANIFESTACIÓN DE LA FALLA
1.1 DEFORMACIÓN ELÁSTICA
1.2 DEFORMACIÓN PLÁSTICA
1.3 RUPTURA (FRACTURA)
1.4 CAMBIO DE MATERIAL: Metalúrgico, químico o
   atómico
2. FACTORES
2.1 CARGAS (FZAS O MOMENTOS):
• ESTÁTICA
• TRANSITORIA
• CÍCLICA
• ALEATORIA
2.2 TIEMPO
• MUY CORTO
• CORTO
• LARGO

2.3 TEMPERATURA
• BAJA
• AMBIENTE
• ELEVADA
• ESTACIONARIA
• TRANSITORIA
• CÍCLICA O ALEATORIA
2.4 AMBIENTE ACTIVO (AGRESIVO)
• QUÍMICO
• NUCLEAR


3. LOCALIZACIÓN DE LA FALLA
3.1 CUERPO
3.2 SUPERFICIE
MODOS DE FALLA OBSERVADOS EN LA PRÁCTICA
1. DEFORMACIÓN ELÁSTICA
2. FLUENCIA
3. BRINELLING (cargas excesiva o de impacto en cojinetes inmóviles. Es
    una forma de daño mecánico en la cual el metal se desplaza sin desgaste)

4. RUPTURA DÚCTIL
5. RUPTURA FRÁGIL
6. FATIGA
•   MUCHOS CICLOS (>10000)
•   BAJOS CICLOS (< 1000)
•   TÉRMICA
•   POR IMPACTO
•   SUPERFICIAL , Y CORROSIÓN
•   FRETTING (2 metales son mantenidos en contacto y sujetos a una repetición de
    deslizamientos cortos con movimientos relativos)
7. CORROSIÓN
•   ATAQUE QUÍMICO DIRECTO
•   GALVÁNICA
•   CREEVICE
•   PITTING
•   INTERGRANULAR
•   POR EROSIÓN
•   POR CAVITACIÓN
•   DAÑO POR HIDRÓGENO
•   BIOLÓGICA
•   POR ESFUERZOS

8. IMPACTO
•   FRACTURA
•   DEFORMACIÓN
•   DESGASTE
•   FRETTING
•   FATIGA
9. DESGASTE
•   ADHESIVO
•   ABRASIVO
•   CORROSIVO
•   FATIGA SUPERFICIAL
•   POR DEFORMACIÓN (FATIGA REPETIDA)
•   POR IMPACTO

10.FRETTING
•   FATIGA
•   DESGASTE
•   CORROSIÓN


11.CREEP
12.RELAX TÉRMICO
13.RUPTURA POR ESFUERZO
14.CHOQUE TÉRMICO
15.GALLING (Forma de desgaste en la cual ocurre un
  cizallamiento ó disminución de la superficie)

16.SPALLING -occurs at high stress contact points, for
  example, in a ball bearing. Spalling occurs in preference to
  brinelling where the maximal shear stress occurs not at the
  surface, but just below, shearing the spall off. (are flakes of a
  material that are broken off a larger solid body and can be
  produced by a variety of mechanisms:projectile impact,
  corrosion, weathering, cavitation, or excessive rolling
  pressure.

17.DAÑO POR RADIACIÓN
18.PANDEO (INESTABILIDAD ELÁSTICA)
19.PANDEO POR CREEP
20.CORROSIÓN POR ESFUERZO
21.DESGASTE POR CORROSIÓN
3. ANÁLISIS DE CARGAS
Reliability Services in the Design Phase
Fault Tree Analysis (FTA)

DEFINITION
Fault Tree Analysis (FTA) is a top-down approach to failure mode analysis. An
FTA identifies failures and strives to eliminate the cause of the failure.

SITUATION
While troubleshooting a failure or trying to identify possible causes to a specific
failure effect, an FTA can be a very useful tool.

OBJECTIVE
FTA is a systematic, deductive method for defining a single specific undesirable
event and determining all possible failures that could cause the event in question
to occur.

VALUE TO YOUR ORGANIZATION
Although an FTA can be very useful in the initial product design phase as an
evaluation tool, it is probably more powerful as a troubleshooting tool after an
event (or proposed event) has taken place.
RELIABILITY INTEGRATION
An example of Reliability Integration during Fault Tree Analysis is as follows:
Using FTA's during HALT planning
When a FMECA identifies a critical effect, an FTA is often deployed to evaluate all
possible failure modes that can also cause the same critical effect. This is especially
helpful when planning a HALT so that the appropriate stresses can be applied and so
that the failure can easily be troubleshot if the critical effect is exposed during HALT.
METHODOLOGY
When we perform an FTA, we start with an undesired event. The undesired event
constitutes the top event in a fault tree diagram. We then brainstorm (just like the
FMECA) as to the possible failure modes that can result in this undesired effect.
FTA's and FMECA's are very similar in this regard but the goal is much different.
Whereas a FMECA is trying to identifying all possible failure modes in a system and
the effects of these failure modes, an FTA starts with one specific failure effect and
then identifies only those failure modes that can cause the particular effect.
How we decide whether to use an FTA or a FMECA
FTA is preferred over FMECA when:
• A small number of top events can be identified
• Product functionality is highly complex
• The product is not repairable once initiated
FMECA is preferred over FTA when:
• The events cannot be limited to a small number
• Multiple successful functional profiles are possible
• Identification of "all possible" failure modes is important
CASE STUDIES/OPTIONS
The following case studies and options provide example approaches. We shall
tailor our approach to meet your specific situation.
1) Using FTA's to Identify Safety-Critical Failures
A Computer manufacturer had a safety-critical failure in their product and they
wanted to identify if there were any other failure modes in the product that could
result in the same failure effect. For this, we turned to an FTA. We made the
safety-critical failure the top event. From there, we reviewed the FMECA and
held brainstorming sessions to help identify other failure modes that could
cause this top event. Next, we reviewed the reliability prediction to identify how
often the event will occur.
2) Using FTA's During Failure Analysis
For a Medical Device company, we showed them how to use FTA as a powerful
failure analysis tool after a failure occurred to help identify the cause of the
failure. Troubleshooting isolated which component failed but an FTA was
needed to determine what caused the failure.
Failure Modes Effects and Criticality Analysis (FMECA)

DEFINITION
In a FMECA, each failure mode of the product is identified and then evaluated for criticality
This criticality is then translated into a risk, and if this level of risk is not acceptable, correc
action must be taken. Risk Management is a process for identifying hazards associated w
a product, estimating and evaluating the associated risks, controlling these risks, and
monitoring the effectiveness of the control. The process includes Risk Analysis, Risk
Evaluation, and Risk Control. Risk Management uses a Failure Modes, Effects, and
Criticality Analysis (FMECA) as a tool when evaluating and controlling risks.
SITUATION
FMECA's are performed not only on the hardware design but on the software, the
manufacturing processes used to build the product, and the user interfaces (everyday
and abuse as well as preventive maintenance tasks).
Whenever a user is involved, we must pay specific attention to the possibility of the user
using the product incorrectly, risking either the integrity of the product or, worse, possibly
creating an unsafe situation.
OBJECTIVE
The objective of a FMECA is the early identification of all catastrophic and critical failure
possibilities so that they can be eliminated or minimized through design correction at the
earliest possible time.
VALUE TO YOUR ORGANIZATION
By understanding the critical failure modes of a design and their effects, we can perform a
risk assessment and if the risk is deemed too high, we can work to mitigate the failure mod
thereby reducing the risk.
Diagrama de cuerpo libre de un auto viajando a
velocidad constante
Diagrama de cuerpo libre de un auto con aceleración
Equilibrio de momentos en el eje X para motor,
transmisión y eje de propulsión de un automóvil de
propulsión trasera (T = engine torque, R = trans-mission
torque ration; el motor gira en sentido CCW visto desde la
transmisión).
                                   .
                                   .
                                   .

DCL de la transmisión y sus principales componentes:
(a) montaje completo. (Continúa)
                           .
                           .




 (b) Eje principal
(front and rear halves rotate freely with respect to each other). (c)
Countershaft.
Free-body diagram of transmission and major components: (d) Housing.
Note: Diameters of gears A and C are 2 ¼ in. Diameters of gears B and D
are 3 ¾ in.
Cargas actuantes en un sección interna resultantes de
un DCL.
Cargas actuantes en un sección interna resultantes de
un DCL.
 Elemento sujeto a 3
 fuerzas: manivela (2)
 unida por medio de un
 pivote al marco fijo (1).
 Una barra horizaontal
 que no se muestra (3)
 se acopla a la parte
 superior, ejerciendo
 una fuerza F de 40lbs.
 Determinar F12 y F42




Solución analítica.
Solución gráfica
Estudios de fuerzas en un dedo
Ejemplo de viga cargada y diagramas de cortante y
flector
Contraeje de transmisión, determinación de sección
crítica
Carga en la seción crítica del contraeje
  Localización de secciones críticas-flujo de
  fuerzas




Conexión en forma de horquilla
Force flow lines and critical sections in yoke
connection.
Force-flow concept applied to triple-riveted butt joint.
(a) complete joint, broken at center, showing total load
carried by straps. (Continued on next four slides.)
Force-flow concept applied to triple-riveted butt joint.
(b) Force flow through plate to rivets. (c) Diagram of
force flow versus plate cross-sectional area.
Force-flow concept applied to triple-riveted butt joint.
(d) Force flow through rivet. (e) Diagrammatic
representation of force flow through rivet.
Force-flow concept applied to triple-riveted butt joint. (f)
Complete diagrammatic representation of force flow.

								
To top